480 results on '"Chitnis, Nakul"'
Search Results
152. A mathematical model for the dynamics of malaria in mosquitoes feeding on a heterogeneous host population
- Author
-
Chitnis, Nakul, primary, Smith, Thomas, additional, and Steketee, Richard, additional
- Published
- 2008
- Full Text
- View/download PDF
153. Some Discrete Competition Models and the Competitive Exclusion Principle†
- Author
-
Cushing, J.M., primary, Levarge, Sheree, additional, Chitnis, Nakul, additional, and Henson, Shandelle M., additional
- Published
- 2004
- Full Text
- View/download PDF
154. MATHEMATICAL MODELS OF CONTACT PATTERNS BETWEEN AGE GROUPS FOR PREDICTING THE SPREAD OF INFECTIOUS DISEASES.
- Author
-
DEL VALLE, SARA Y., HYMAN, AMES M., and CHITNIS, NAKUL
- Published
- 2013
- Full Text
- View/download PDF
155. Effects of pyrethroid resistance on the cost effectiveness of a mass distribution of longlasting insecticidal nets: a modelling study.
- Author
-
Briët, Olivier J. T., Penny, Melissa A., Hardy, Diggory, Awolola, Taiwo S., Van Bortel, Wim, Corbel, Vincent, Dabiré, Roch K., Etang, Josiane, Koudou, Benjamin G., Tungu, Patrick K., and Chitnis, Nakul
- Subjects
PYRETHROIDS ,INSECTICIDE-treated mosquito nets ,EPIDEMIOLOGY ,PIPERONYL butoxide ,DISEASE susceptibility ,COST effectiveness - Abstract
Background: The effectiveness of insecticide-treated nets in preventing malaria is threatened by developing resistance against pyrethroids. Little is known about how strongly this affects the effectiveness of vector control programmes. Methods: Data from experimental hut studies on the effects of long-lasting, insecticidal nets (LLINs) on nine anopheline mosquito populations, with varying levels of mortality in World Health Organization susceptibility tests, were used to parameterize malaria models. Both simple static models predicting population-level insecticidal effectiveness and protection against blood feeding, and complex dynamic epidemiological models, where LLINs decayed over time, were used. The epidemiological models, implemented in Open Malaria, were employed to study the impact of a single mass distribution of LLINs on malaria, both in terms of episodes prevented during the effective lifetime of the batch of LLINs, and in terms of net health benefits (NHB) expressed in disability-adjusted life years (DALYs) averted during that period, depending on net type (standard pyrethroid-only LLIN or pyrethroidpiperonyl butoxide combination LLIN), resistance status, coverage and pre-intervention transmission level. Results: There were strong positive correlations between insecticide susceptibility status and predicted population level insecticidal effectiveness of and protection against blood feeding by LLIN intervention programmes. With the most resistant mosquito population, the LLIN mass distribution averted up to about 40% fewer episodes and DALYs during the effective lifetime of the batch than with fully susceptible populations. However, cost effectiveness of LLINs was more sensitive to the pre-intervention transmission level and coverage than to susceptibility status. For four out of the six Anopheles gambiae sensu lato populations where direct comparisons between standard LLINs and combination LLINs were possible, combination nets were more cost effective, despite being more expensive. With one resistant population, both net types were equally effective, and with one of the two susceptible populations, standard LLINs were more cost effective. Conclusion: Despite being less effective when compared to areas with susceptible mosquito populations, standard and combination LLINs are likely to (still) be cost effective against malaria even in areas with strong pyrethroid resistance. Combination nets are likely to be more cost effective than standard nets in areas with resistant mosquito populations. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
156. Correction to: Evaluation of different deployment strategies for larviciding to control malaria: a simulation study.
- Author
-
Runge, Manuela, Mapua, Salum, Nambunga, Ismail, Smith, Thomas A., Chitnis, Nakul, Okumu, Fredros, and Pothin, Emilie
- Subjects
MALARIA prevention - Abstract
This first sentence used to read "Larviciding against malaria vectors in Africa has been limited to indoor residual spraying and insecticide treated nets but is increasingly being considered by some countries as a complementary strategy". Correction to: Evaluation of different deployment strategies for larviciding to control malaria: a simulation study However, the sentence should read as "Larviciding against malaria vectors in Africa has been limited compared to indoor residual spraying and insecticide treated nets but is increasingly being considered by some countries as a complementary strategy.". [Extracted from the article]
- Published
- 2021
- Full Text
- View/download PDF
157. Field evaluation of a volatile pyrethroid spatial repellent and etofenprox treated clothing for outdoor protection against forest malaria vectors in Cambodia.
- Author
-
Vajda, Élodie A., Ross, Amanda, Doum, Dyna, Fairbanks, Emma L., Chitnis, Nakul, Hii, Jeffrey, Moore, Sarah J., Richardson, Jason H., Macdonald, Michael, Sovannaroth, Siv, Kimheng, Pen, McIver, David J., Tatarsky, Allison, and Lobo, Neil F.
- Abstract
Cambodia’s goal to eliminate malaria by 2025 is challenged by persistent transmission in forest and forest fringe areas, where people are exposed to Anopheles mosquito bites during the day and night. Volatile pyrethroid spatial repellents (VPSRs) and insecticide-treated clothing (ITC) could address these gaps. This study evaluated the outdoor application of one passive transfluthrin-based VPSR, four etofenprox-ITCs paired with a picaridin topical repellent, and a combination of VPSR and ITC against wild Anopheles landing in Cambodia. A 7 × 7 Latin-square study was conducted over 49 collection nights in temporary open structures in Mondulkiri Province. All interventions substantially reduced Anopheles landing, with protective efficacy ranging from 61 to 95%. Mathematical modeling showed significant reductions in vectoral capacity, especially with the combined ITC and VPSR and VPSR alone, albeit with decreased effectiveness over time. These interventions have the potential to reduce outdoor and daytime Anopheles biting, offering valuable contributions to malaria elimination efforts in Cambodia and the Greater Mekong Subregion, contingent upon achieving effective coverage and adherence. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
158. Resurgence of malaria infection after mass treatment: a simulation study.
- Author
-
Smith, Thomas A., Pemberton-Ross, Peter, Penny, Melissa A., and Chitnis, Nakul
- Subjects
MALARIA ,PLASMODIUM falciparum ,VECTOR control ,CONCEPTUAL models ,STOCHASTIC models ,GLUCOSE-6-phosphate dehydrogenase deficiency - Abstract
Background: Field studies are evaluating if mass drug administration (MDA) might shorten the time to elimination of Plasmodium falciparum malaria, when vector control measures and reactive surveillance strategies are scaled-up. A concern with this strategy is that there may be resurgence of transmission following MDA. Methods: A conceptual model was developed to classify possible outcomes of an initial period of MDA, followed by continuously implementing other interventions. The classification considered whether elimination or a new endemic stable state is achieved, and whether changes are rapid, transient, or gradual. These categories were informed by stability analyses of simple models of vector control, case management, and test-and-treat interventions. Individual-based stochastic models of malaria transmission (OpenMalaria) were then used to estimate the probability and likely rates of resurgence in realistic settings. Effects of concurrent interventions, including routine case management and test-and-treat strategies were investigated. Results: Analysis of the conceptual models suggest resurgence will occur after MDA unless transmission potential is very low, or the post-MDA prevalence falls below a threshold, which depends on both transmission potential and on the induction of bistability. Importation rates are important only when this threshold is very low. In most OpenMalaria simulations the approximately stable state achieved at the end of the simulations was independent of inclusion of MDA and the final state was unaffected by importation of infections at plausible rates. Elimination occurred only with high effective coverage of case management, low initial prevalence, and high intensity test-and-treat. High coverage of case management but not by test-and-treat induced bistability. Where resurgence occurred, its rate depended mainly on transmission potential (not treatment rates). Conclusions: A short burst of high impact MDA is likely to be followed by resurgence. To avert resurgence, concomitant interventions need either to substantially reduce average transmission potential or to be differentially effective in averting or clearing infections at low prevalence. Case management at high effective coverage has this differential effect, and should suffice to avert resurgence caused by imported cases at plausible rates of importation. Once resurgence occurs, its rate depends mainly on transmission potential, not on treatment strategies. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
159. Evaluating human landing catches as a measure of mosquito biting and the importance of considering additional modes of action.
- Author
-
Fairbanks, Emma L, Tambwe, Mgeni M., Moore, Jason, Mpelepele, Ahmed, Lobo, Neil F., Mashauri, Rajabu, Chitnis, Nakul, and Moore, Sarah J.
- Abstract
Entomological evaluations of vector control tools often use human landing catches (HLCs) as a standard measure of a direct human-vector contact. However, some tools have additional characteristics, such as mortality, and HLCS are not sensitive for measuring other effects beyond landing inhibition. Therefore, additional measures may need to be considered when evaluating these tools for public health use. This study has two main aims (1) the evaluate the accuracy of HLCs as a proxy for feeding and (2) to compare the predicted reduction in vectorial capacity when we do and do not consider these additional characteristics. To achieve this, we analyse previously published semi-field data from an experiment which used HLCs and another where mosquitoes were allowed to feed in the presence of different dosages of the volatile pyrethroid spatial repellent, transfluthrin. We compare results for two mathematical models: one which only considers the reduction in feeding effect and one which also considers mortality before and after feeding (using data gathered by the aspiration of mosquitoes after the semi-field feeding/landing period and 24 h survival monitoring). These Bayesian hierarchical models are parameterised using Bayesian inference. We observe that, for susceptible mosquitoes, reduction in landing is underestimated by HLCs. For knockdown resistant mosquitoes the relationship is less clear; with HLCs sometimes appearing to overestimate this characteristic. We find HLCs tend to under-predict the relative reduction in vectorial capacity in susceptible mosquitoes while over-predicting this impact in knockdown-resistant mosquitoes. Models without secondary effects have lower predicted relative reductions in vectorial capacities. Overall, this study highlights the importance of considering additional characteristics to reduction in biting of volatile pyrethroid spatial repellents. We recommend that these are considered when evaluating novel vector control tools. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
160. Accelerating Progress Towards the 2030 Neglected Tropical Diseases Targets: How Can Quantitative Modeling Support Programmatic Decisions?
- Author
-
Vasconcelos, Andreia, King, Jonathan D, Nunes-Alves, Cláudio, Anderson, Roy, Argaw, Daniel, Basáñez, Maria-Gloria, Bilal, Shakir, Blok, David J, Blumberg, Seth, Borlase, Anna, Brady, Oliver J, Browning, Raiha, Chitnis, Nakul, Coffeng, Luc E, Crowley, Emily H, Cucunubá, Zulma M, Cummings, Derek A T, Davis, Christopher Neil, Davis, Emma Louise, and Dixon, Matthew
- Subjects
- *
INFECTIOUS disease transmission , *TROPICAL medicine , *POLICY sciences , *HUMAN services programs , *DECISION making , *HEALTH planning , *NEGLECTED diseases , *MATHEMATICAL models , *THEORY , *SARS-CoV-2 - Abstract
Over the past decade, considerable progress has been made in the control, elimination, and eradication of neglected tropical diseases (NTDs). Despite these advances, most NTD programs have recently experienced important setbacks; for example, NTD interventions were some of the most frequently and severely impacted by service disruptions due to the coronavirus disease 2019 (COVID-19) pandemic. Mathematical modeling can help inform selection of interventions to meet the targets set out in the NTD road map 2021–2030, and such studies should prioritize questions that are relevant for decision-makers, especially those designing, implementing, and evaluating national and subnational programs. In September 2022, the World Health Organization hosted a stakeholder meeting to identify such priority modeling questions across a range of NTDs and to consider how modeling could inform local decision making. Here, we summarize the outputs of the meeting, highlight common themes in the questions being asked, and discuss how quantitative modeling can support programmatic decisions that may accelerate progress towards the 2030 targets. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
161. Abundance of Opisthorchis felineusMetacercariae in cyprinid fish in the middle Ob River basin (Tomsk region, Russia)
- Author
-
Simakova, Anastasia V., Chitnis, Nakul, Babkina, Irina B., Fedorova, Olga S., Fedotova, Marina M., Babkin, Alexandr M., and Khodkevich, Nadezda E.
- Abstract
Infection with the liver fluke, Opisthorchis felineus, caused by the consumption of infected raw or undercooked cyprinid fish is common in humans and carnivores in the middle Ob River basin (Tomsk region, Russia) and can lead to diseases in humans. The goal of this study was the status of fish infection with O. felineus metacercariae in order to assess the role of fish in the infection of the human population in the middle Ob River basin.
- Published
- 2021
- Full Text
- View/download PDF
162. Theory of reactive interventions in the elimination and control of malaria.
- Author
-
Chitnis, Nakul, Pemberton-Ross, Peter, Yukich, Josh, Hamainza, Busiku, Miller, John, Reiker, Theresa, Eisele, Thomas P., and Smith, Thomas A.
- Subjects
- *
MALARIA , *INDEX numbers (Economics) - Abstract
Background: Reactive case detection (RCD) is an integral part of many malaria control and elimination programmes and can be conceived of as a way of gradually decreasing transmission. However, it is unclear under what circumstances RCD may have a substantial impact on prevalence, how likely it is to lead to local elimination, or how effective it needs to be to prevent reintroduction after transmission has been interrupted. Methods: Analyses and simulations of a discrete time compartmental susceptible-infectious-susceptible (SIS) model were used to understand the mechanisms of how RCD changes transmission dynamics and estimate the impact of RCD programmes in a range of settings with varying patterns of transmission potential and programme characteristics. Prevalence survey data from recent studies in Zambia were used to capture the effects of spatial clustering of patent infections. Results: RCD proved most effective at low prevalence. Increasing the number of index cases followed was more important than increasing the number of neighbours tested per index case. Elimination was achieved only in simulations of situations with very low transmission intensity and following many index cases. However, RCD appears to be helpful in maintaining the disease-free state after achieving malaria elimination (through other interventions). Conclusion: RCD alone can eliminate malaria in only a very limited range of settings, where transmission potential is very low, and improving the coverage of RCD has little effect on this range. In other settings, it is likely to reduce disease burden. RCD may also help maintain the disease-free state in the face of imported infections. Prevalence survey data can be used to estimate a targeting ratio (the ratio of prevalence found through RCD to that in the general population) which is an important determinant of the effect of RCD. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
163. Models of effectiveness of interventions against malaria transmitted by Anopheles albimanus.
- Author
-
Briët, Olivier J. T., Impoinvil, Daniel E., Chitnis, Nakul, Pothin, Emilie, Lemoine, Jean Frantz, Frederic, Joseph, and Smith, Thomas A.
- Subjects
ANOPHELES ,MALARIA ,ANOPHELES gambiae ,PLASMODIUM falciparum ,VECTOR control - Abstract
Background: Most impact prediction of malaria vector control interventions has been based on African vectors. Anopheles albimanus, the main vector in Central America and the Caribbean, has higher intrinsic mortality, is more zoophilic and less likely to rest indoors. Therefore, relative impact among interventions may be different. Prioritizing interventions, in particular for eliminating Plasmodium falciparum from Haiti, should consider local vector characteristics. Methods: Field bionomics data of An. albimanus from Hispaniola and intervention effect data from southern Mexico were used to parameterize mathematical malaria models. Indoor residual spraying (IRS), insecticide-treated nets (ITNs), and house-screening were analysed by inferring their impact on the vectorial capacity in a difference-equation model. Impact of larval source management (LSM) was assumed linear with coverage. Case management, mass drug administration and vaccination were evaluated by estimating their effects on transmission in a susceptible-infected-susceptible model. Analogous analyses were done for Anopheles gambiae parameterized with data from Tanzania, Benin and Nigeria. Results: While LSM was equally effective against both vectors, impact of ITNs on transmission by An. albimanus was much lower than for An. gambiae. Assuming that people are outside until bedtime, this was similar for the impact of IRS with dichlorodiphenyltrichloroethane (DDT) or bendiocarb, and impact of IRS was less than that of ITNs. However, assuming people go inside when biting starts, IRS had more impact on An. albimanus than ITNs. While house-screening had less impact than ITNs or IRS on An. gambiae, it had more impact on An. albimanus than ITNs or IRS. The impacts of chemoprevention and chemotherapy were comparable in magnitude to those of strategies against An. albimanus. Chemo-prevention impact increased steeply as coverage approached 100%, whilst clinical-case management impact saturated because of remaining asymptomatic infections. Conclusions: House-screening and repellent IRS are potentially highly effective against An. albimanus if people are indoors during the evening. This is consistent with historical impacts of IRS with DDT, which can be largely attributed to excito-repellency. It also supports the idea that housing improvements have played a critical role in malaria control in North America. For elimination planning, impact estimates need to be combined with feasibility and cost-analysis. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
164. Modelling reactive case detection strategies for interrupting transmission of Plasmodium falciparum malaria.
- Author
-
Reiker, Theresa, Chitnis, Nakul, and Smith, Thomas
- Subjects
- *
PLASMODIUM falciparum , *MALARIA , *STOCHASTIC models , *VACCINATION - Abstract
Background: As areas move closer to malaria elimination, a combination of limited resources and increasing heterogeneity in case distribution and transmission favour a shift to targeted reactive interventions. Reactive case detection (RCD), the following up of additional individuals surrounding an index case, has the potential to target transmission pockets and identify asymptomatic cases in them. Current RCD implementation strategies vary, and it is unclear which are most effective in achieving elimination. Methods: OpenMalaria, an established individual-based stochastic model, was used to simulate RCD in a Zambia-like setting. The capacity to follow up index cases, the search radius, the initial transmission and the case management coverage were varied. Suitable settings were identified and probabilities of elimination and time to elimination estimated. The value of routinely collected prevalence and incidence data for predicting the success of RCD was assessed. Results: The results indicate that RCD with the aim of transmission interruption is only appropriate in settings where initial transmission is very low (annual entomological inoculation rate (EIR) 1–2 or prevalence approx. < 7–19% depending on case management levels). Every index case needs to be followed up, up to a maximum case-incidence threshold which defines the suitability threshold of settings for elimination using RCD. Increasing the search radius around index cases is always beneficial. Conclusions: RCD is highly resource intensive, requiring testing and treating of 400–500 people every week for 5–10 years for a reasonable chance of elimination in a Zambia-like setting. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
165. Future use-cases of vaccines in malaria control and elimination
- Author
-
Penny, Melissa A., Camponovo, Flavia, Chitnis, Nakul, Smith, Thomas A., and Tanner, Marcel
- Subjects
3. Good health
166. Role of mass drug administration in elimination of Plasmodium falciparum malaria: a consensus modelling study
- Author
-
Brady, Oliver J., Slater, Hannah C., Pemberton-Ross, Peter James, Wenger, Edward, Maude, Richard J., Ghani, Azra C., Penny, Melissa A., Gerardin, Jaline, White, Lisa J., Chitnis, Nakul, Aguas, Ricardo, Hay, Simon I., Smith, David L., Stuckey, Erin M., Okiro, Emelda A, Smith, Thomas A., and Okell, Lucy C.
- Subjects
3. Good health
167. Potential causes and consequences of behavioural resilience and resistance in malaria vector populations : a mathematical modelling analysis
- Author
-
Killeen, Gerry F. and Chitnis, Nakul
- Subjects
2. Zero hunger ,3. Good health
168. Modelling the impact of insecticide-based control interventions on the evolution of insecticide resistance and disease transmission
- Author
-
Barbosa, Susana, Kay, Katherine, Chitnis, Nakul, and Hastings, Ian M.
- Subjects
3. Good health
169. Assessing the impact of aggregating disease stage data in model predictions of human African trypanosomiasis transmission and control activities in Bandundu province (DRC)
- Author
-
Castaño, María Soledad, Ndeffo-Mbah, Martial L., Rock, Kat S., Palmer, Cody, Knock, Edward, Mwamba Miaka, Erick, Ndung'u, Joseph M., Torr, Steve, Verlé, Paul, Spencer, Simon E. F., Galvani, Alison, Bever, Caitlin, Keeling, Matt J., and Chitnis, Nakul
- Subjects
3. Good health
170. Modeling the cost effectiveness of malaria control interventions in the highlands of western Kenya
- Author
-
Stuckey, Erin M., Stevenson, Jennifer, Galactionova, Katya, Baidjoe, Amrish Y., Bousema, Teun, Odongo, Wycliffe, Kariuki, Simon, Drakeley, Chris, Smith, Thomas A., Cox, Jonathan, and Chitnis, Nakul
- Subjects
3. Good health
171. Mathematical Analysis of the Transmission Dynamics of the Liver Fluke, Opisthorchis viverrini
- Author
-
Bürli, Christine, Harbrecht, Helmut, Odermatt, Peter, Sayasone, Somphou, and Chitnis, Nakul
- Subjects
3. Good health
172. Attacking the mosquito on multiple fronts: insights from the vector control optimization model (VCOM) for malaria elimination
- Author
-
Kiware, Samson S., Chitnis, Nakul, Tatarsky, Allison, Wu, Sean, Castellanos, Héctor Manuel Sánchez, Gosling, Roly, Smith, David, and Marshall, John M.
- Subjects
3. Good health
173. Mathematical analysis of the transmission dynamics of the liver fluke, Opisthorchis viverrini
- Author
-
Bürli, Christine, Harbrecht, Helmut, Odermatt, Peter, Sayasone, Somphou, and Chitnis, Nakul
- Subjects
3. Good health
174. Modeling the persistence of Opisthorchis viverrini worm burden after mass-drug administration and education campaigns with systematic adherence.
- Author
-
Kamber, Lars, Bürli, Christine, Harbrecht, Helmut, Odermatt, Peter, Sayasone, Somphou, and Chitnis, Nakul
- Subjects
- *
OPISTHORCHIS viverrini , *PARASITE life cycles , *CHOLANGIOCARCINOMA , *WORMS , *LIVER flukes - Abstract
Opisthorchis viverrini is a parasitic liver fluke contracted by consumption of raw fish, which affects over 10 million people in Southeast Asia despite sustained control efforts. Chronic infections are a risk factor for the often fatal bile duct cancer, cholangiocarcinoma. Previous modeling predicted rapid elimination of O. viverrini following yearly mass drug administration (MDA) campaigns. However, field data collected in affected populations shows persistence of infection, including heavy worm burden, after many years of repeated interventions. A plausible explanation for this observation is systematic adherence of individuals in health campaigns, such as MDA and education, with some individuals consistently missing treatment. We developed an agent-based model of O. viverrini which allows us to introduce various heterogeneities including systematic adherence to MDA and education campaigns at the individual level. We validate the agent-based model by comparing it to a previously published population-based model. We estimate the degree of systematic adherence to MDA and education campaigns indirectly, using epidemiological data collected in Lao PDR before and after 5 years of repeated MDA, education and sanitation improvement campaigns. We predict the impact of interventions deployed singly and in combination, with and without the estimated systematic adherence. We show how systematic adherence can substantially increase the time required to achieve reductions in worm burden. However, we predict that yearly MDA campaigns alone can result in a strong reduction of moderate and heavy worm burden, even under systematic adherence. We predict latrines and education campaigns to be particularly important for the reduction in overall prevalence, and therefore, ultimately, elimination. Our findings show how systematic adherence can explain the observed persistence of worm burden; while emphasizing the benefit of interventions for the entire population, even under systematic adherence. At the same time, the results highlight the substantial opportunity to further reduce worm burden if patterns of systematic adherence can be overcome. Author summary: Opisthorchis viverrini is a liver parasite contracted by consumption of raw fish which affects over 10 million people in Southeast Asia despite sustained control efforts, with heavy infections being a major risk factor for often fatal bile duct cancer. Efforts to reduce the worm burden in populations include education of individuals on the safe consumption of fish meals, improvement of sanitation to interrupt the parasitic life cycle and mass drug administration campaigns, where ideally all targeted individuals of a population receive a drug against the parasite without a prior test of whether they are infected. We present a new agent-based mathematical model of Opisthorchis viverrini transmission and control. This model allows us to include systematic adherence to interventions, which describes the pattern of some individuals consistently being missed by interventions aimed at an entire (sub-)population. Our findings show how systematic adherence can explain the observed persistence of worm burden, but how interventions can be greatly beneficial even for individuals that systematically miss treatment. At the same time, we show the substantial opportunity to further reduce worm burden if patterns of systematic adherence can be overcome. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
175. Modelling the impact of insecticide-based control interventions on the evolution of insecticide resistance and disease transmission.
- Author
-
Barbosa, Susana, Kay, Katherine, Chitnis, Nakul, and Hastings, Ian M.
- Subjects
INSECTICIDE application ,MOSQUITOES ,MALARIA ,PROTOZOAN diseases ,BLACKWATER fever - Abstract
Background: Current strategies to control mosquito-transmitted infections use insecticides targeted at various stages of the mosquito life-cycle. Control is increasingly compromised by the evolution of insecticide resistance but there is little quantitative understanding of its impact on control effectiveness. We developed a computational approach that incorporates the stage-structured mosquito life-cycle and allows tracking of insecticide resistant genotypes. This approach makes it possible to simultaneously investigate: (i) the population dynamics of mosquitoes throughout their whole life-cycle; (ii) the impact of common vector control interventions on disease transmission; (iii) how these interventions drive the spread of insecticide resistance; and (iv) the impact of resistance once it has arisen and, in particular, whether it is sufficient for malaria transmission to resume. The model consists of a system of difference equations that tracks the immature (eggs, larvae and pupae) and adult stages, for males and females separately, and incorporates density-dependent regulation of mosquito larvae in breeding sites. Results: We determined a threshold level of mosquitoes below which transmission of malaria is interrupted. It is based on a classic Ross-Macdonald derivation of the malaria basic reproductive number (R
0 ) and may be used to assess the effectiveness of different control strategies in terms of whether they are likely to interrupt disease transmission. We simulated different scenarios of insecticide deployment by changing key parameters in the model to explore the comparative impact of insecticide treated nets, indoor residual spraying and larvicides. Conclusions: Our simulated results suggest that relatively low degrees of resistance (in terms of reduced mortality following insecticide contact) can induce failure of interventions, and the rate of spread of resistance is faster when insecticides target the larval stages. The optimal disease control strategy depends on vector species demography and local environmental conditions but, in our illustrative parametrisation, targeting larval stages achieved the greatest reduction of the adult population, followed by targeting of non-host-seeking females, as provided by indoor residual spraying. Our approach is designed to be flexible and easily generalizable to many scenarios using different calibrations and to diseases other than malaria. [ABSTRACT FROM AUTHOR]- Published
- 2018
- Full Text
- View/download PDF
176. The development and evaluation of a self-marking unit to estimate malaria vector survival and dispersal distance.
- Author
-
Saddler, Adam, Kreppel, Katharina S., Chitnis, Nakul, Smith, Thomas A., Denz, Adrian, Moore, Jason D., Tambwe, Mgeni M., and Moore, Sarah J.
- Subjects
- *
INSECTICIDE-treated mosquito nets , *ANOPHELES arabiensis , *ANOPHELES gambiae , *MALARIA , *COUMARINS , *DISEASE vectors , *CULEX - Abstract
Background: A clear understanding of mosquito biology is fundamental to the control efforts of mosquito-borne diseases such as malaria. Mosquito mark-release-recapture (MMRR) experiments are a popular method of measuring the survival and dispersal of disease vectors; however, examples with African malaria vectors are limited. Ethical and technical difficulties involved in carrying out MMRR studies may have held back research in this area and, therefore, a device that marks mosquitoes as they emerge from breeding sites was developed and evaluated to overcome the problems of MMRR. Methods: A modified self-marking unit that marks mosquitoes with fluorescent pigment as they emerge from their breeding site was developed based on a previous design for Culex mosquitoes. The self-marking unit was first evaluated under semi-field conditions with laboratory-reared Anopheles arabiensis to determine the marking success and impact on mosquito survival. Subsequently, a field evaluation of MMRR was conducted in Yombo village, Tanzania, to examine the feasibility of the system. Results: During the semi-field evaluation the self-marking units successfully marked 86% of emerging mosquitoes and there was no effect of fluorescent marker on mosquito survival. The unit successfully marked wild male and female Anopheles gambiae sensu lato (s.l.) in sufficiently large numbers to justify its use in MMRR studies. The estimated daily survival probability of An. gambiae s.l. was 0.87 (95% CI 0.69–1.10) and mean dispersal distance was 579 m (95% CI 521–636 m). Conclusions: This study demonstrates the successful use of a self-marking device in an MMRR study with African malaria vectors. This method may be useful in investigating population structure and dispersal of mosquitoes for deployment and evaluation of future vector control tools, such as gene drive, and to better parameterize mathematical models. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
177. Investigation of optimized observation periods for estimating a representative home range of free-roaming domestic dogs.
- Author
-
Sousa, Filipe Maximiano, Warembourg, Charlotte, Abakar, Mahamat Fayiz, Alvarez, Danilo, Berger-Gonzalez, Monica, Odoch, Terence, Wera, Ewaldus, Chitnis, Nakul, Silva, Laura Cunha, Alobo, Grace, Sikko, Maria M., Roquel, Pablo, Hernández, Alexis Leonel López, and Dürr, Salome
- Abstract
Free-roaming domestic dogs (FRDD), as vectors of zoonotic diseases, are of high relevance for public health. Understanding roaming patterns of dogs can help to design disease control programs and disease transmission simulation models. Studies on GPS tracking of dogs report stark differences in recording periods. So far, there is no accepted number of days required to capture a representative home range (HR) of FRDD. The objective of this study was to evaluate changes in HR size and shape over time of FRDD living in Chad, Guatemala, Indonesia and Uganda and identify the period required to capture stable HR values. Dogs were collared with GPS units, leading to a total of 46 datasets with, at least, 19 recorded days. For each animal and recorded day, HR sizes were estimated using the Biased Random Bridge method and percentages of daily change in size and shape calculated and taken as metrics. The analysis revealed that the required number of days differed substantially between individuals, isopleths, and countries, with the extended HR (95% isopleth value) requiring a longer recording period. To reach a stable HR size and shape values for 75% of the dogs, 26 and 21 days, respectively, were sufficient. However, certain dogs required more extended observational periods. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
178. Treatment outcome in an SI model with evolutionary resistance: a Darwinian model for the evolution of resistance.
- Author
-
Cushing, J. M., Park, Junpyo, Farrell, Alex, and Chitnis, Nakul
- Subjects
- *
TREATMENT effectiveness , *EVOLUTIONARY models , *NATURAL immunity , *INFECTIOUS disease transmission - Abstract
We consider a Darwinian (evolutionary game theoretic) version of a standard susceptible-infectious SI model in which the resistance of the disease causing pathogen to a treatment that prevents death to infected individuals is subject to evolutionary adaptation. We determine the existence and stability of all equilibria, both disease-free and endemic, and use the results to determine conditions under which the treatment will succeed or fail. Of particular interest are conditions under which a successful treatment in the absence of resistance adaptation (i.e. one that leads to a stable disease-free equilibrium) will succeed or fail when pathogen resistance is adaptive. These conditions are determined by the relative breadths of treatment effectiveness and infection transmission rate distributions as functions of pathogen resistance. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
179. Vaccination of dogs in an African city interrupts rabies transmission and reduces human exposure
- Author
-
Zinsstag, Jakob, Lechenne, Monique, Laager, Mirjam, Mindekem, Rolande, Naïssengar, Service, Oussiguéré, Assandi, Bidjeh, Kebkiba, Rives, Germain, Tessier, Julie, Madjaninan, Seraphin, Ouagal, Mahamat, Moto, Daugla D., Alfaroukh, Idriss O., Muthiani, Yvonne, Traoré, Abdallah, Hattendorf, Jan, Lepelletier, Anthony, Kergoat, Lauriane, Bourhy, Hervé, Dacheux, Laurent, Stadler, Tanja, and Chitnis, Nakul
- Published
- 2017
- Full Text
- View/download PDF
180. Testing and treatment for malaria elimination: a systematic review.
- Author
-
Newby, Gretchen, Cotter, Chris, Roh, Michelle E., Harvard, Kelly, Bennett, Adam, Hwang, Jimee, Chitnis, Nakul, Fine, Sydney, Stresman, Gillian, Chen, Ingrid, Gosling, Roly, and Hsiang, Michelle S.
- Subjects
- *
MALARIA , *EMPIRICAL research - Abstract
Background: Global interest in malaria elimination has prompted research on active test and treat (TaT) strategies. Methods: A systematic review and meta-analysis were conducted to assess the effectiveness of TaT strategies to reduce malaria transmission. Results: A total of 72 empirical research and 24 modelling studies were identified, mainly focused on proactive mass TaT (MTaT) and reactive case detection (RACD) in higher and lower transmission settings, respectively. Ten intervention studies compared MTaT to no MTaT and the evidence for impact on malaria incidence was weak. No intervention studies compared RACD to no RACD. Compared to passive case detection (PCD) alone, PCD + RACD using standard diagnostics increased infection detection 52.7% and 11.3% in low and very low transmission settings, respectively. Using molecular methods increased this detection of infections by 1.4- and 1.1-fold, respectively. Conclusion: Results suggest MTaT is not effective for reducing transmission. By increasing case detection, surveillance data provided by RACD may indirectly reduce transmission by informing coordinated responses of intervention targeting. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
181. A randomized, double-blind placebo-control study assessing the protective efficacy of an odour-based 'push–pull' malaria vector control strategy in reducing human-vector contact.
- Author
-
Fillinger, Ulrike, Denz, Adrian, Njoroge, Margaret M., Tambwe, Mohamed M., Takken, Willem, van Loon, Joop J. A., Moore, Sarah J., Saddler, Adam, Chitnis, Nakul, and Hiscox, Alexandra
- Subjects
- *
MALARIA prevention , *MOSQUITO control , *INSECTICIDE-treated mosquito nets , *VECTOR control , *ANOPHELES arabiensis , *ANOPHELES - Abstract
Novel malaria vector control strategies targeting the odour-orientation of mosquitoes during host-seeking, such as 'attract-and-kill' or 'push-and-pull', have been suggested as complementary tools to indoor residual spraying and long-lasting insecticidal nets. These would be particularly beneficial if they can target vectors in the peri-domestic space where people are unprotected by traditional interventions. A randomized double-blind placebo-control study was implemented in western Kenya to evaluate: a 'push' intervention (spatial repellent) using transfluthrin-treated fabric strips positioned at open eave gaps of houses; a 'pull' intervention placing an odour-baited mosquito trap at a 5 m distance from a house; the combined 'push–pull' package; and the control where houses contained all elements but without active ingredients. Treatments were rotated through 12 houses in a randomized-block design. Outdoor biting was estimated using human landing catches, and indoor mosquito densities using light-traps. None of the interventions provided any protection from outdoor biting malaria vectors. The 'push' reduced indoor vector densities dominated by Anopheles funestus by around two thirds. The 'pull' device did not add any benefit. In the light of the high Anopheles arabiensis biting densities outdoors in the study location, the search for efficient outdoor protection and effective pull components needs to continue. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
182. Correction: Testing and treatment for malaria elimination: a systematic review.
- Author
-
Newby, Gretchen, Cotter, Chris, Roh, Michelle E., Harvard, Kelly, Bennett, Adam, Hwang, Jimee, Chitnis, Nakul, Fine, Sydney, Stresman, Gillian, Chen, Ingrid, Gosling, Roly, and Hsiang, Michelle S.
- Subjects
- *
MALARIA - Abstract
This document is a correction notice for an article titled "Testing and treatment for malaria elimination: a systematic review" published in the Malaria Journal. The authors have identified two errors in the Results section and one clarification in the caption of Figure 4. The first error was due to an inconsistency between the updated figure and the accompanying text, while the second error occurred during the transfer of information between documents. The clarification was made to prevent misinterpretation of the relative ratios presented in Figure 4. The corrected text and table have been provided in the notice. The authors apologize for any inconvenience caused. [Extracted from the article]
- Published
- 2024
- Full Text
- View/download PDF
183. Leveraging mathematical models of disease dynamics and machine learning to improve development of novel malaria interventions.
- Author
-
Golumbeanu, Monica, Yang, Guo-Jing, Camponovo, Flavia, Stuckey, Erin M., Hamon, Nicholas, Mondy, Mathias, Rees, Sarah, Chitnis, Nakul, Cameron, Ewan, and Penny, Melissa A.
- Subjects
- *
MACHINE dynamics , *MACHINE learning , *MALARIA , *MEDICAL model , *MATHEMATICAL models - Abstract
Background: Substantial research is underway to develop next-generation interventions that address current malaria control challenges. As there is limited testing in their early development, it is difficult to predefine intervention properties such as efficacy that achieve target health goals, and therefore challenging to prioritize selection of novel candidate interventions. Here, we present a quantitative approach to guide intervention development using mathematical models of malaria dynamics coupled with machine learning. Our analysis identifies requirements of efficacy, coverage, and duration of effect for five novel malaria interventions to achieve targeted reductions in malaria prevalence. Methods: A mathematical model of malaria transmission dynamics is used to simulate deployment and predict potential impact of new malaria interventions by considering operational, health-system, population, and disease characteristics. Our method relies on consultation with product development stakeholders to define the putative space of novel intervention specifications. We couple the disease model with machine learning to search this multi-dimensional space and efficiently identify optimal intervention properties that achieve specified health goals. Results: We apply our approach to five malaria interventions under development. Aiming for malaria prevalence reduction, we identify and quantify key determinants of intervention impact along with their minimal properties required to achieve the desired health goals. While coverage is generally identified as the largest driver of impact, higher efficacy, longer protection duration or multiple deployments per year are needed to increase prevalence reduction. We show that interventions on multiple parasite or vector targets, as well as combinations the new interventions with drug treatment, lead to significant burden reductions and lower efficacy or duration requirements. Conclusions: Our approach uses disease dynamic models and machine learning to support decision-making and resource investment, facilitating development of new malaria interventions. By evaluating the intervention capabilities in relation to the targeted health goal, our analysis allows prioritization of interventions and of their specifications from an early stage in development, and subsequent investments to be channeled cost-effectively towards impact maximization. This study highlights the role of mathematical models to support intervention development. Although we focus on five malaria interventions, the analysis is generalizable to other new malaria interventions. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
184. Incidence and consequences of damage to insecticide-treated mosquito nets in Kenya.
- Author
-
Smith, Thomas, Denz, Adrian, Ombok, Maurice, Bayoh, Nabie, Koenker, Hannah, Chitnis, Nakul, Briet, Olivier, Yukich, Joshua, and Gimnig, John E.
- Subjects
- *
INSECTICIDE-treated mosquito nets , *ORDINARY differential equations , *FLOW charts , *PLASMODIUM falciparum - Abstract
Background: Efforts to improve the impact of long-lasting insecticidal nets (LLINs) should be informed by understanding of the causes of decay in effect. Holes in LLINs have been estimated to account for 7–11% of loss in effect on vectorial capacity for Plasmodium falciparum malaria in an analysis of repeated cross-sectional surveys of LLINs in Kenya. This does not account for the effect of holes as a cause of net attrition or non-use, which cannot be measured using only cross-sectional data. There is a need for estimates of how much these indirect effects of physical damage on use and attrition contribute to decay in effectiveness of LLINs. Methods: Use, physical integrity, and survival were assessed in a cohort of 4514 LLINs followed for up to 4 years in Kenya. Flow diagrams were used to illustrate how the status of nets, in terms of categories of use, physical integrity, and attrition, changed between surveys carried out at 6-month intervals. A compartment model defined in terms of ordinary differential equations (ODEs) was used to estimate the transition rates between the categories. Effects of physical damage to LLINs on use and attrition were quantified by simulating counterfactuals in which there was no damage. Results: Allowing for the direct effect of holes, the effect on use, and the effect on attrition, 18% of the impact on vectorial capacity was estimated to be lost because of damage. The estimated median lifetime of the LLINs was 2.9 years, but this was extended to 5.7 years in the counterfactual without physical damage. Nets that were in use were more likely to be in a damaged state than unused nets but use made little direct difference to LLIN lifetimes. Damage was reported as the reason for attrition for almost half of attrited nets, but the model estimated that almost all attrited nets had suffered some damage before attrition. Conclusions: Full quantification of the effects of damage will require measurement of the supply of new nets and of household stocks of unused nets, and also of their impacts on both net use and retention. The timing of mass distribution campaigns is less important than ensuring sufficient supply. In the Kenyan setting, nets acquired damage rapidly once use began and the damage led to rapid attrition. Increasing the robustness of nets could substantially increase their lifetime and impact but the impact of LLIN programmes on malaria transmission is ultimately limited by levels of use. Longitudinal analyses of net integrity data from different settings are needed to determine the importance of physical damage to nets as a driver of attrition and non-use, and the importance of frequent use as a cause of physical damage in different contexts. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
185. Predicting the impact of outdoor vector control interventions on malaria transmission intensity from semi-field studies.
- Author
-
Denz, Adrian, Njoroge, Margaret M., Tambwe, Mgeni M., Champagne, Clara, Okumu, Fredros, van Loon, Joop J. A., Hiscox, Alexandra, Saddler, Adam, Fillinger, Ulrike, Moore, Sarah J., and Chitnis, Nakul
- Subjects
- *
MALARIA prevention , *VECTOR control , *MALARIA , *ANOPHELES arabiensis , *MOSQUITOES , *ANOPHELES - Abstract
Background: Semi-field experiments with human landing catch (HLC) measure as the outcome are an important step in the development of novel vector control interventions against outdoor transmission of malaria since they provide good estimates of personal protection. However, it is often infeasible to determine whether the reduction in HLC counts is due to mosquito mortality or repellency, especially considering that spatial repellents based on volatile pyrethroids might induce both. Due to the vastly different impact of repellency and mortality on transmission, the community-level impact of spatial repellents can not be estimated from such semi-field experiments. Methods: We present a new stochastic model that is able to estimate for any product inhibiting outdoor biting, its repelling effect versus its killing and disarming (preventing host-seeking until the next night) effects, based only on time-stratified HLC data from controlled semi-field experiments. For parameter inference, a Bayesian hierarchical model is used to account for nightly variation of semi-field experimental conditions. We estimate the impact of the products on the vectorial capacity of the given Anopheles species using an existing mathematical model. With this methodology, we analysed data from recent semi-field studies in Kenya and Tanzania on the impact of transfluthrin-treated eave ribbons, the odour-baited Suna trap and their combination (push–pull system) on HLC of Anopheles arabiensis in the peridomestic area. Results: Complementing previous analyses of personal protection, we found that the transfluthrin-treated eave ribbons act mainly by killing or disarming mosquitoes. Depending on the actual ratio of disarming versus killing, the vectorial capacity of An. arabiensis is reduced by 41 to 96% at 70% coverage with the transfluthrin-treated eave ribbons and by 38 to 82% at the same coverage with the push–pull system, under the assumption of a similar impact on biting indoors compared to outdoors. Conclusions: The results of this analysis of semi-field data suggest that transfluthrin-treated eave ribbons are a promising tool against malaria transmission by An. arabiensis in the peridomestic area, since they provide both personal and community protection. Our modelling framework can estimate the community-level impact of any tool intervening during the mosquito host-seeking state using data from only semi-field experiments with time-stratified HLC. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
186. Evaluation of different deployment strategies for larviciding to control malaria: a simulation study.
- Author
-
Runge, Manuela, Mapua, Salum, Nambunga, Ismail, Smith, Thomas A., Chitnis, Nakul, Okumu, Fredros, and Pothin, Emilie
- Subjects
- *
MALARIA prevention , *ANOPHELES gambiae , *MOSQUITOES , *SEASONS , *MALARIA , *BIOSPHERE - Abstract
Background: Larviciding against malaria vectors in Africa has been limited compared to indoor residual spraying and insecticide treated nets but is increasingly being considered by some countries as a complementary strategy. However, despite progress towards improved larvicides and new tools for mapping or treating mosquito-breeding sites, little is known about the optimal deployment strategies for larviciding in different transmission and seasonality settings. Methods: A malaria transmission model, OpenMalaria, was used to simulate varying larviciding strategies and their impact on host-seeking mosquito densities, entomological inoculation rate (EIR) and malaria prevalence. Variations in coverage, duration, frequency, and timing of larviciding were simulated for three transmission intensities and four transmission seasonality profiles. Malaria transmission was assumed to follow rainfall with a lag of one month. Theoretical sub-Saharan African settings with Anopheles gambiae as the dominant vector were chosen to explore impact. Relative reduction compared to no larviciding was predicted for each indicator during the simulated larviciding period. Results: Larviciding immediately reduced the predicted host-seeking mosquito densities and EIRs to a maximum that approached or exceeded the simulated coverage. Reduction in prevalence was delayed by approximately one month. The relative reduction in prevalence was up to four times higher at low than high transmission. Reducing larviciding frequency (i.e., from every 5 to 10 days) resulted in substantial loss in effectiveness (54, 45 and 53% loss of impact for host-seeking mosquito densities, EIR and prevalence, respectively). In seasonal settings the most effective timing of larviciding was during or at the beginning of the rainy season and least impactful during the dry season, assuming larviciding deployment for four months. Conclusion: The results highlight the critical role of deployment strategies on the impact of larviciding. Overall, larviciding would be more effective in settings with low and seasonal transmission, and at the beginning and during the peak densities of the target species populations. For maximum impact, implementers should consider the practical ranges of coverage, duration, frequency, and timing of larviciding in their respective contexts. More operational data and improved calibration would enable models to become a practical tool to support malaria control programmes in developing larviciding strategies that account for the diversity of contexts. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
187. Predicted Impact of COVID-19 on Neglected Tropical Disease Programs and the Opportunity for Innovation.
- Author
-
Toor, Jaspreet, Adams, Emily R, Aliee, Maryam, Amoah, Benjamin, Anderson, Roy M, Ayabina, Diepreye, Bailey, Robin, Basáñez, Maria-Gloria, Blok, David J, Blumberg, Seth, Borlase, Anna, Rivera, Rocio Caja, Castaño, María Soledad, Chitnis, Nakul, Coffeng, Luc E, Crump, Ronald E, Das, Aatreyee, Davis, Christopher N, Davis, Emma L, and Deiner, Michael S
- Subjects
- *
NEGLECTED diseases , *ELEPHANTIASIS , *HELMINTHIASIS , *COVID-19 , *MATHEMATICAL models , *TROPICAL medicine , *PUBLIC health , *NATIONAL health services , *SCHISTOSOMIASIS , *DRUG administration , *THEORY , *TRYPANOSOMIASIS , *INFECTIOUS disease transmission , *ONCHOCERCIASIS , *TRACHOMA , *DIFFUSION of innovations , *GOAL (Psychology) - Abstract
Due to the COVID-19 pandemic, many key neglected tropical disease (NTD) activities have been postponed. This hindrance comes at a time when the NTDs are progressing towards their ambitious goals for 2030. Mathematical modelling on several NTDs, namely gambiense sleeping sickness, lymphatic filariasis, onchocerciasis, schistosomiasis, soil-transmitted helminthiases (STH), trachoma, and visceral leishmaniasis, shows that the impact of this disruption will vary across the diseases. Programs face a risk of resurgence, which will be fastest in high-transmission areas. Furthermore, of the mass drug administration diseases, schistosomiasis, STH, and trachoma are likely to encounter faster resurgence. The case-finding diseases (gambiense sleeping sickness and visceral leishmaniasis) are likely to have fewer cases being detected but may face an increasing underlying rate of new infections. However, once programs are able to resume, there are ways to mitigate the impact and accelerate progress towards the 2030 goals. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
188. Modelling disease persistence and elimination in low-transmission settings
- Author
-
Das, Aatreyee Mimi, Chitnis, Nakul, Fink, Günther, and Gerardin, Jaline
- Abstract
Malaria and human African trypanosomiasis are two vector-borne diseases caused by protozoa. In Zanzibar, Tanzania, malaria persists at a low prevalence despite the implementation of vector control, passive surveillance, and reactive surveillance. Human movement, and subsequent case importation, is hypothesised to be a key driver of persistence. Human African trypanosomiasis prevalence is below 1000 globally and is targeted for elimination. However, treatment options were previously limited and the diagnosis process is invasive and painful. The introduction of a new oral treatment improves options for treatment but may have an impact on transmission, as compliance levels may be lower than with previous treatments. Stochastic metapopulation models of disease transmission were used to explore a range of questions regarding malaria and human African trypanosomiasis transmission and elimination. A metapopulation model of malaria transmission was developed and parameterised to data from Zanzibar, Tanzania. It incorporated human movement and reactive case detection, and was used to investigate the impact of improvements to reactive case detection or treatment of imported cases on prevalence levels. The model was then expanded to include separate categories for imported, introduced, and indigenous cases, which allowed us to apply the WHO definition of malaria elimination (three years with no indigenous cases). An already established model of human African trypanosomiasis transmission was adapted to incorporate treatment by fexinidazole and potential non-compliance. This was used to test the potential impact of widespread versus limited access to fexinidazole under a range of compliance scenarios, and the potential impact of increased treatment seeking rates. The controlled reproduction number for malaria was estimated to be below the threshold value of 1 on both major islands of Zanzibar, confirming that importation is driving disease persistence. Reactive case detection is estimated to reduce malaria incidence by approximately 10% on Zanzibar. To achieve non-zero probabilities of elimination, infections in travellers need to be targeted, and onward transmission from imported cases needs to be reduced. Considering human African trypanosomiasis transmission, an increase of 20% in the passive detection rate is expected to counter a small negative impact of non-compliance to fexinidazole. While reactive case detection is useful for surveillance and does reduce malaria incidence, the large number of low parasite density infections prevents reactive case detection from removing large parts of the parasite reservoir. The controlled reproduction number needs to be kept well below 1 in order to minimise the chances of any imported cases leading to chains of transmission that lead to indigenous cases. A better understanding of treatment compliance with fexinidazole and changes in treatment seeking behaviour is necessary to better estimate the potential impact of fexinidazole on human African trypanosomiasis transmission in the Democratic Republic of the Congo.
- Published
- 2023
189. Do Cryptic Reservoirs Threaten Gambiense-Sleeping Sickness Elimination?
- Author
-
Büscher, Philippe, Bart, Jean-Mathieu, Boelaert, Marleen, Bucheton, Bruno, Cecchi, Giuliano, Chitnis, Nakul, Courtin, David, Figueiredo, Luisa M., Franco, José-Ramon, Grébaut, Pascal, Hasker, Epco, Ilboudo, Hamidou, Jamonneau, Vincent, Koffi, Mathurin, Lejon, Veerle, MacLeod, Annette, Masumu, Justin, Matovu, Enock, Mattioli, Raffaele, and Noyes, Harry
- Subjects
- *
TRYPANOSOMA brucei , *INFECTIOUS disease transmission , *TSETSE-flies , *COMMUNICABLE diseases , *PUBLIC health - Abstract
Trypanosoma brucei gambiense causes human African trypanosomiasis (HAT). Between 1990 and 2015, almost 440 000 cases were reported. Large-scale screening of populations at risk, drug donations, and efforts by national and international stakeholders have brought the epidemic under control with <2200 cases in 2016. The World Health Organization (WHO) has set the goals of gambiense -HAT elimination as a public health problem for 2020, and of interruption of transmission to humans for 2030. Latent human infections and possible animal reservoirs may challenge these goals. It remains largely unknown whether, and to what extend, they have an impact on gambiense -HAT transmission. We argue that a better understanding of the contribution of human and putative animal reservoirs to gambiense- HAT epidemiology is mandatory to inform elimination strategies. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
190. Mathematical modelling of transmission dynamics of Opisthorchis viverrini
- Author
-
Bürli, Christine, Chitnis, Nakul, and Anderson, Roy
- Subjects
parasitic diseases - Abstract
The trematode liver fluke, Opisthorchis viverrini, is endemic in Thailand, Lao People's Democratic Republic (Lao PDR) and Cambodia. Its life cycle involves humans, dogs and cats as definitive hosts; and snails and fish as intermediate hosts. Humans get infected through the consumption of raw or undercooked fish. A severe infection of O. viverrini can lead to cholangiocarcinoma, a mostly fatal bile duct cancer. Control activities include treatment of humans and domestic pets, health education on food consumption and improved sanitation. Mathematical modelling can help us to understand this multi-host disease system, identify weak points in the transmission cycle and determine the effectiveness of combinations of interventions to provide rational advice for the planning of control activities. Analysis and simulation of a series of mathematical models, ranging from deterministic ordinary differential equations models to stochastic individual-based models, calibrated to data from two islands in the Mekong river in Lao PDR, suggest that (i) mass drug administration is necessary for elimination of O. viverrini to be achieved as quickly as possible; (ii) sustainable education campaigns are as important as mass drug administration; and (iii) it is unlikely that cats and dogs are necessary for transmission to persist.
- Published
- 2021
- Full Text
- View/download PDF
191. Chapter Three - Mathematical Models of Human African Trypanosomiasis Epidemiology.
- Author
-
Rock, Kat S., Stone, Chris M., Hastings, Ian M., Keeling, Matt J., Torr, Steve J., and Chitnis, Nakul
- Subjects
- *
TREATMENT of African trypanosomiasis , *TRYPANOSOMIASIS , *COMMUNICABLE diseases , *MATHEMATICAL models , *EPIDEMIOLOGY , *TRYPANOSOMA , *TSETSE-flies , *DISEASE prevalence , *INFECTIOUS disease transmission - Abstract
Human African trypanosomiasis (HAT), commonly called sleeping sickness, is caused by Trypanosoma spp. and transmitted by tsetse flies (Glossina spp.). HAT is usually fatal if untreated and transmission occurs in foci across sub-Saharan Africa. Mathematical modelling of HAT began in the 1980s with extensions of the Ross-Macdonald malaria model and has since consisted, with a few exceptions, of similar deterministic compartmental models. These models have captured the main features of HAT epidemiology and provided insight on the effectiveness of the two main control interventions (treatment of humans and tsetse fly control) in eliminating transmission. However, most existing models have overestimated prevalence of infection and ignored transient dynamics. There is a need for properly validated models, evolving with improved data collection, that can provide quantitative predictions to help guide control and elimination strategies for HAT. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
192. Understanding the epidemiology and transmission of tuberculosis among adults in rural and urban Tanzania
- Author
-
Hella, Jerry, Gagneux, Sebastien, Chitnis, Nakul, and de Jong, Bouke Catherine
- Abstract
Background: Tuberculosis (TB) is the leading cause of death in the world from a single infectious disease and resulted in about 1.5 million deaths in 2018. Globally, close to one third of the population is latently infected with Mycobacterium tuberculosis (Mtb), of which about 5-10% during their lifetime, will develop active TB depending on the age of infection. TB is an airborne disease transmitted by airways from one person to the next when an uninfected individual breathes in air containing Mtb expired from an infected person. One way to estimate the risk of TB transmission begins with measuring environmental levels of carbon dioxide (CO2) levels exhaled by humans. CO2 levels combined with social contact data allow calculation of the volumes of rebreathed air in order to estimate the potential for airborne disease transmission by considering time at risk, quanta of contagion and the number of people occupying the confined space etc. Unfortunately, most TB patients are diagnosed at later stages of the disease, due to poor health-seeking behavior, inappropriate diagnostic investigations requested by health care providers, and limited access to better TB diagnostics which forces patients to seek relief by using self-prescribed medication. Delaying diagnosis and treatment of TB has important consequences for disease control at both the individual (poor treatment outcome) as well as the community level (continued transmission). Within the country, the prevalence of TB varies considerably across regions, and is higher among males, older persons, and those with lower socioeconomic status. Lastly, patients with TB often have additional comorbidities such as anemia, helminthiasis etc., which can result in poor treatment outcomes. Anemia of chronic disease is primarily found in patients with chronic disease status such as those with chronic immune activation such as TB and HIV-positive patients. Objectives: The overall goal of this PhD project was to understand the epidemiology and transmission of tuberculosis in Tanzania by studying the infrastructure-related risk of TB transmission through measuring environmental CO2 levels at locations of public importance; determining the TB diagnostic delay and its associated factors among TB patients; understanding differences in the epidemiology of TB and comorbidities among TB patients from rural and urban Tanzania; and investigating the association of hepcidin levels with coinfections, TB disease severity and progression from TB infection to disease among adults in Tanzania. Methods: This PhD project was embedded in the ongoing hospital-based cohort of adult TB cases and controls in Temeke, Dar es Salaam and Ifakara, Morogoro, Tanzania. The field work for this PhD study was carried out between September 2016 and April 2018. The project had two designs; infrastructure-related and patient-related design. For objective 1, an observational study was carried out which employed exposure assessment methods where we collected environmental data (CO2, geo-coordinates etc.,) from locations of public importance. We used the modified Wells-Riley equation to estimate the annual risk of TB transmission which was calculated as a function of time spent per year at a given location. For objectives 2-3, we analysed data from the ongoing cohort of adult TB patients and their household contacts (TB DAR). Briefly, recruitment of study participants began in 2013 at Temeke Regional Referral Hospital (Temeke district) and 2014 at the St. Francis Referral Hospital (Kilombero district). Participants collected baseline information and provided specimen for further analysis. Multivariate logistic regression models were used to find associations and presented as crude and adjusted odds ratio. Lastly, for objective 4, we designed a nested case-control study matched by age and sex. Descriptive statistics were used to summarize participants characteristics. We compared cases and controls using conditional logistic regression model to determine associations between outcomes of interest and various predictors. Results: We found that the annual risks of TB transmission were highest among prison inmates (41.6%) and drivers (20.3%) in public transport. Lower transmission risks were found in central markets (4.8% for traders, but 0.5% for their customers), passengers on public transport (2.4%), public schools (4.0%), nightclubs (1.7%), religious (0.13%), and social halls (0.12%). Diagnostic delay was positively associated with absence of chest pain (aOR = 7.97, 95% confidence intervals [CI] = 3.15 – 20.19), and presence of hemoptysis (aOR = 25.37, 95% CI = 11.15 – 57.74) and negatively associated with use of medication prior to TB diagnosis (aOR = 0.31, 95% CI = 0.14 – 0.71). Patients living far from pharmacies were less likely to visit a health care facility (incremental increase of distance versus visit to any facility: OR = 0.51, 95% CI = 0.28 – 0.96). Patients from the rural setting were older (median age 37 years vs. 34 years, p=0.003), had a lower median body mass index (17.5 kg/m2 vs. 18.5 kg/m2, p
- Published
- 2019
- Full Text
- View/download PDF
193. Mathematical modelling of dog rabies transmission in N’Djamena, Chad
- Author
-
Laager, Mirjam, Utzinger, Jürg, Chitnis, Nakul, and Keeling, Matt
- Abstract
Rabies is a viral disease that is transmitted by bite and is fatal after the onset of symptoms. All warm blooded animals are susceptible to rabies and a wide range of species including foxes, wolves, jackals, raccoons, mongooses and bats act as reservoir hosts. Approximately 60,000 people die of rabies every year, mainly in Africa and Asia. The main source of human rabies is the domestic dog. Rabies in humans is preventable by timely administration of post-exposure prophylaxis, with a reduced schedule of administration if the person was protected by pre-exposure prophylaxis. Mass vaccination of dogs is considered effective in preventing human exposure and oral vaccine baits were used to eliminate rabies from foxes in central and western Europe. In N’Djamena, the capital of Chad, rabies is endemic with approximately one confirmed case of dog rabies per week. Each dog exposes on average two humans. In 2012 and 2013 two mass vaccination campaigns of dogs were conducted, reaching a coverage of more than 70% in both years. The campaigns interrupted transmission for nine months, but a resurgence of cases led to re-establishment of rabies at the pre-intervention endemic state. To better understand the movement and contact behaviour of dogs, 300 geo-located contact sensors were deployed on dogs in three different quarters of N’Djamena in 2016. We developed three mathematical models of rabies transmission, calibrated to the incidence data and coverage levels from the campaigns and data on dog movement and contacts from the geo-located contact sensors. We used an ordinary differential equation model to assess the effect of the vaccination campaigns and found that after the campaigns, the effective reproductive ratio dropped below one. Implementing a stochastic version of the model with the Gillespie algorithm confirmed the interruption of transmission. We found that population turnover contributed more to the decrease of vaccination coverage after the campaigns than individual immunity loss. Possible reasons for the resurgence of cases after the campaigns include spatial heterogeneity of vaccination coverage and dog density, underreporting and importation of latent dogs from the surroundings of N’Djamena. We developed a deterministic metapopulation model with importation of latent dogs to investigate the potential reasons for the resurgence seen in 2014. Our results indicate that importation of latently infected dogs better explains the incidence data than heterogeneity or underreporting. Because importation seems to be the most likely reason for the resurgence in cases, we investigated the chains of transmission triggered by imported cases. In order to realistically reproduce the contact heterogeneity at individual level, we used data from 300 geo-located contact sensors to build a network of 5000 dogs. Since there is no established method for expanding a network to a network with more nodes, we have developed and validated a network construction algorithm. We developed an individual based model and calibrated the transmission rate such that the simulation results correspond to outbreak data from two quarters in N’Djamena. We have shown that 70% coverage prevents major but not minor outbreaks. Since highly connected dogs hold a critical role in rabies transmission, vaccinating such dogs could increase the effect of vaccination strategies. Vaccinating dogs is an effective and equitable way of reducing human exposure and should therefore be an inherent of part rabies control programmes in endemic settings. However, in the absence of dog population management, population turnover quickly reduces vaccination coverage and reintroduction from surrounding areas or spillovers from wildlife reservoirs threaten the gains of mass dog vaccination campaigns. This suggests that maintaining high vaccination coverage by either repeated mass vaccination campaigns or continuous vaccination of dogs as well as oral vaccination of reservoirs (which was not investigated here) might be part of the best intervention package for settings like N’Djamena.
- Published
- 2018
194. Application of mathematical modeling for malaria control decision-making in settings of varying transmission intensity
- Author
-
Stuckey, Erin Mae, Chitnis, Nakul, and Kleinschmidt, Immo
- Subjects
parasitic diseases - Abstract
Planning for the control of Plasmodium falciparum malaria at the population level demands models of malaria epidemiology that provide realistic quantitative prediction of likely epidemiological outcomes of a wide range of control strategies. This project applies mathematical modeling parameterized both generally and with site-specific field data to better understand transmission dynamics of malaria across sites with varying transmission intensity and seasonality, primarily the highlands of western Kenya and in the lowlands of Zambia's Southern Province. Simulation results explore possible epidemiological scenarios for malaria in the presence and absence of a mix of control interventions, and for different amounts and patterns of seasonality of transmission. Together with a cost effectiveness analysis, results form the basis of recommendations for control programs. Individual-based stochastic models of malaria epidemiology were developed by the Swiss Tropical and Public Health Institute (Swiss TPH). To provide the site-specific parameters needed to fit the models to the study areas data on existing entomological, demographic, intervention deployment and health systems was gathered from field studies conducted by collaborating institutes and a literature review. Model simulations were run on an ensemble of models with multiple random seeds on the OpenMalaria simulator. Simulation outputs were compared to the observed data from the study areas in order to assess the validity of the model and a sensitivity analysis was conducted to address uncertainty. The model was then used to predict the impact of different combinations of malaria control interventions, and the impact of different seasonal transmission patterns, on impact measures. The models were able to simulate the transmission patterns of malaria in the study areas of western Kenyan highlands and Zambia lowlands and gain insight into the potential impact of malaria control interventions currently being un- or under- utilized in these areas. Despite the ability of mathematical modeling to be used to translate between measures of malaria transmission and indicators of disease burden in areas where sparse data renders evidence-based programmatic decision-making challenging, these models remain largely inaccessible to program managers. Results from such models can provide public health officials with accurate estimates of transmission, by seasonal pattern, that are necessary for assessing and tailoring malaria control and elimination programs to specific settings.
- Published
- 2015
- Full Text
- View/download PDF
195. Mathematical modelling of mosquito dispersal for malaria vector control
- Author
-
Lutambi, Angelina M., Smith, Thomas A., Ghani, Azra, Chitnis, Nakul, and Penny, Melissa
- Subjects
fungi ,parasitic diseases - Abstract
In malaria endemic regions, dispersal of mosquitoes from one location to another searching for resources for their survival and reproduction is a fundamental biological process that operates at multiple temporal and spatial scales. This dispersal behaviour is an important factor that causes uneven distribution of malaria vectors causing heterogeneous transmission. Although mosquito dependence in a heterogeneous environment has several implications for malaria vector control and in public health in general, its inclusion in mathematical models of malaria transmission and control has received limited attention. Most models of malaria transmission and control explain relationships between the number of mosquitoes and malaria transmission in humans while assuming enclosed systems of mosquitoes in which spatial dynamics and movements are not taken into account. These models have limited ability to assess and quantify the distribution of risks and interventions at local scales. Therefore, in order to overcome this limitation, mathematical models that consider the interaction between dispersal behaviour, population dynamics, environmental heterogeneity, and age structures of the mosquito are needed for designing, planning, and management of the control strategies at local scales. Advances in malaria modelling have recently begun to incorporate spatial heterogeneity and highlight the need for more spatial explicit models that include all the vital components of ecological interactions. In response to this need, this thesis develops a spatial mathematical model that captures mosquito dispersal and includes all of the above characteristics to achieve a broader and deeper understanding of mosquito foraging behaviour, population dynamics, and its interactions with environmental heterogeneity, distribution of malaria risk, and vector control interventions. The model is applied to assess the impact of dispersal and heterogeneous distribution of mosquito resources on the spatial distribution, dynamics, and persistence of mosquito populations, to estimate the distance travelled by mosquitoes, and to evaluate and assess the impact of spatial distribution of vector control interventions on effectiveness of interventions under mosquitoes' natural dispersal behaviour. Chapter 2 develops a spatial mathematical model of mosquito dispersal in heterogeneous environments with a framework that is simple to allow investigation of aspects that affects malaria transmission. The model incorporates age distribution in form of the aquatic and adult stages of the mosquito life cycle and further divides the adult mosquito population into three stages of the mosquitoes searching for hosts, those resting, and those searching for oviposition sites. These three adult stages provide an opportunity to study the life style of the adult mosquito, and also offer a direct opportunity to assess the impact of interventions targeting different adult states such as insecticide treated bednets (ITNs), indoor residual spraying (IRS), and spatial repellents that reduce contacts between host seeking mosquitoes and human hosts. The spatial characteristics of the model are based on discretization of space into discrete patches. Host and oviposition site searching mosquitoes disperse to the nearest neighbours across the spatial platform where hosts and breeding sites are distributed. In the same Chapter, the model is applied to investigate the effect of heterogeneous distribution of resources used by mosquitoes, estimate the dispersal distance, and to assess the impact of spatial repellents on the dispersal distance. Results revealed that due to dispersal, the distribution of mosquitoes highly depend on the distribution of hosts and breeding sites and the random distribution of spatial repellents reduces the distance travelled by mosquitoes; offering a promising vector control strategy for malaria. In addition, analysis indicated that when only a single patch is considered, and movement ignored, the recruitment parameter and parameters related to the larval and host seeking stages of the mosquito strongly determine mosquito population persistence and extinction. Chapter 3 extends the model developed in Chapter 2 to include vector control interventions. As vector control intervention deployment plans need to consider the spatial distribution of intervention packages, the model extension developed in this chapter is used to examine the effect of spatial arrangement of vector control interventions on their effectiveness. Application of the model to IRS, larvicide, and ITNs showed that randomly distributing these interventions will in general be more effective than clustering them on side of an area. Mosquito dispersal and the different patterns of heterogeneity have different effects on population distribution and dynamics of mosquitoes, and thus, that of malaria. Models that incorporate dispersal when integrated with environmental heterogeneity allow predictions to capture ecological behaviour of mosquitoes, the main source of variations in malaria risk at local spatial scales, providing information needed for determining risk areas for malaria vector control purposes.
- Published
- 2013
196. Optimizing malaria vector control in the Greater Mekong Subregion: a systematic review and mathematical modelling study to identify desirable intervention characteristics.
- Author
-
Wang Y, Chitnis N, and Fairbanks EL
- Subjects
- Animals, Humans, Feeding Behavior, Asia, Southeastern, Models, Theoretical, Malaria prevention & control, Malaria transmission, Mosquito Vectors physiology, Anopheles physiology, Mosquito Control methods
- Abstract
Background: In the Greater Mekong Subregion (GMS), new vector-control tools are needed to target mosquitoes that bite outside during the daytime and night-time to advance malaria elimination., Methods: We conducted systematic literature searches to generate a bionomic dataset of the main malaria vectors in the GMS, including human blood index (HBI), parity proportion, sac proportion (proportion with uncontracted ovary sacs, indicating the amount of time until they returned to host seeking after oviposition) and the resting period duration. We then performed global sensitivity analyses to assess the influence of bionomics and intervention characteristics on vectorial capacity., Results: Our review showed that Anopheles minimus, An. sinensis, An. maculatus and An. sundaicus display opportunistic blood-feeding behaviour, while An. dirus is more anthropophilic. Multivariate regression analysis indicated that environmental, climatic and sampling factors influence the proportion of parous mosquitoes, and resting duration varies seasonally. Sensitivity analysis highlighted HBI and parity proportion as the most influential bionomic parameters, followed by resting duration. Killing before feeding is always a desirable characteristic across all settings in the GMS. Disarming is also a desirable characteristic in settings with a low HBI. Repelling is only an effective strategy in settings with a low HBI and low parity proportion. Killing after feeding is only a desirable characteristic if the HBI and parity proportions in the setting are high., Conclusions: Although in general adopting tools that kill before feeding would have the largest community-level effect on reducing outdoor transmission, other modes of action can be effective. Current tools in development which target outdoor biting mosquitoes should be implemented in different settings dependent on their characteristics., (© 2024. The Author(s).)
- Published
- 2024
- Full Text
- View/download PDF
197. Inference for entomological semi-field experiments: Fitting a mathematical model assessing personal and community protection of vector-control interventions.
- Author
-
Fairbanks EL, Saeung M, Pongsiri A, Vajda E, Wang Y, McIver DJ, Richardson JH, Tatarsky A, Lobo NF, Moore SJ, Ponlawat A, Chareonviriyaphap T, Ross A, and Chitnis N
- Subjects
- Animals, Humans, Aged, Mosquito Vectors, Mosquito Control methods, Bayes Theorem, Models, Theoretical, Anopheles
- Abstract
The effectiveness of vector-control tools is often assessed by experiments as a reduction in mosquito landings using human landing catches (HLCs). However, HLCs alone only quantify a single characteristic and therefore do not provide information on the overall impacts of the intervention product. Using data from a recent semi-field study which used time-stratified HLCs, aspiration of non-landing mosquitoes, and blood feeding, we suggest a Bayesian inference approach for fitting such data to a stochastic model. This model considers both personal protection, through a reduction in biting, and community protection, from mosquito mortality and disarming (prolonged inhibition of blood feeding). Parameter estimates are then used to predict the reduction of vectorial capacity induced by etofenpox-treated clothing, picaridin topical repellents, transfluthrin spatial repellents and metofluthrin spatial repellents, as well as combined interventions for Plasmodium falciparum malaria in Anopleles minimus. Overall, all interventions had both personal and community effects, preventing biting and killing or disarming mosquitoes. This led to large estimated reductions in the vectorial capacity, with substantial impact even at low coverage. As the interventions aged, fewer mosquitoes were killed; however the impact of some interventions changed from killing to disarming mosquitoes. Overall, this inference method allows for additional modes of action, rather than just reduction in biting, to be parameterised and highlights the tools assessed as promising malaria interventions., Competing Interests: Declaration of competing interest The authors declare no conflict of interest., (Copyright © 2023 The Authors. Published by Elsevier Ltd.. All rights reserved.)
- Published
- 2024
- Full Text
- View/download PDF
198. Repurposing Know-how for Drug Development: Case Studies from the Swiss Tropical and Public Health Institute.
- Author
-
Meier L, Antillon M, Burri C, Chitnis N, Endriss Y, Keiser J, Moore S, Müller P, Penny MA, Voss TS, Mäser P, and Utzinger J
- Subjects
- Humans, Drug Development, Drug Discovery, Switzerland, Drug Repositioning, Public Health
- Abstract
In pursuing novel therapeutic solutions, drug discovery and development rely on efficiently utilising existing knowledge and resources. Repurposing know-how, a strategy that capitalises on previously acquired information and expertise, has emerged as a powerful approach to accelerate drug discovery and development processes, often at a fraction of the costs of de novo developments. For 80 years, collaborating within a network of partnerships, the Swiss Tropical and Public Health Institute (Swiss TPH) has been working along a value chain from innovation to validation and application to combat poverty-related diseases. This article presents an overview of selected know-how repurposing initiatives conducted at Swiss TPH with a particular emphasis on the exploration of drug development pathways in the context of neglected tropical diseases and other infectious diseases of poverty, such as schistosomiasis, malaria and human African trypanosomiasis., (Copyright 2023 Lukas Meier, Marina Antillon, Christian Burri, Nakul Chitnis, Yvette Endriss, Jennifer Keiser, Sarah Moore, Pie Müller, Melissa Penny, Till S. Voss, Pascal Mäser, Jürg Utzinger. License: This work is licensed under a Creative Commons Attribution 4.0 International License.)
- Published
- 2023
- Full Text
- View/download PDF
199. Time series analysis of survival and oviposition cycle duration of Anopheles funestus (Giles) in Mozambique.
- Author
-
Charlwood JD, Smith TA, Kampango A, Tomas EVE, and Chitnis N
- Subjects
- Animals, Male, Female, Oviposition, Mozambique, Time Factors, Mosquito Vectors, Anopheles
- Abstract
Background: Survival and gonotrophic cycle duration are important determinants of the vectorial capacity of malaria vectors but there are a limited number of approaches to estimate these quantities from field data. Time-series of observations of mosquitoes at different stages in the life-cycle are under-used., Methods: Anopheles funestus mosquitoes were caught using various methods over a 7.6-year period in Furvela, Mozambique. Survival and oviposition cycle duration were estimated using (i) an existing time-series approach for analysing dissections of mosquitoes caught in light-traps, extended to allow for variability in the duration of the cycle; (ii) an established approach for estimating cycle duration from resting collection data; (iii) a novel time-series approach fitted to numbers and categories of mosquitoes caught in exit-traps., Results: Data were available from 7,396, 6,041 and 1,527 trap-nights for exit-traps, light-traps and resting collections respectively. Estimates of cycle duration varied considerably between the different methods. The estimated proportion of female mosquitoes surviving each day of 0.740 (95% credible interval [0.650-0.815]) derived from light-trap data was much lower than the estimated daily survival of male mosquitoes from the model fitted to exit-trap data (0.881, 95% credible interval [0.747-0.987]). There was no tendency for the oviposition cycle to become shorter at higher temperature while the odds of survival of females through the cycle was estimated to be multiplied by 1.021 for every degree of mean weekly temperature increase (95% credible interval [0.991-1.051]). There was negligible temperature dependence and little inter-annual variation in male survival., Discussion: The time-series approach fitted to the exit-traps suggests that male An. funestus have higher survival than do females, and that male survival was temperature independent and unaffected by the introduction of long-lasting insecticidal nets (LLINs). The patterns of temperature dependence in females are at variance with results of laboratory studies. Time series approaches have the advantage for estimating survival that they do not depend on representative sampling of mosquitoes over the whole year. However, the estimates of oviposition cycle duration were associated with considerable uncertainty, which appears to be due to variability between insects in the duration of the resting period, and the estimates based on exit-trap data are sensitive to assumptions about relative trapping efficiencies., Competing Interests: The authors declare that they have no competing interests., (© 2023 Charlwood et al.)
- Published
- 2023
- Full Text
- View/download PDF
200. Modelling the impact of interventions on imported, introduced and indigenous malaria infections in Zanzibar, Tanzania.
- Author
-
Das AM, Hetzel MW, Yukich JO, Stuck L, Fakih BS, Al-Mafazy AH, Ali A, and Chitnis N
- Subjects
- Humans, Tanzania epidemiology, Incidence, Prevalence, Movement, Malaria epidemiology, Malaria prevention & control
- Abstract
Malaria cases can be classified as imported, introduced or indigenous cases. The World Health Organization's definition of malaria elimination requires an area to demonstrate that no new indigenous cases have occurred in the last three years. Here, we present a stochastic metapopulation model of malaria transmission that distinguishes between imported, introduced and indigenous cases, and can be used to test the impact of new interventions in a setting with low transmission and ongoing case importation. We use human movement and malaria prevalence data from Zanzibar, Tanzania, to parameterise the model. We test increasing the coverage of interventions such as reactive case detection; implementing new interventions including reactive drug administration and treatment of infected travellers; and consider the potential impact of a reduction in transmission on Zanzibar and mainland Tanzania. We find that the majority of new cases on both major islands of Zanzibar are indigenous cases, despite high case importation rates. Combinations of interventions that increase the number of infections treated through reactive case detection or reactive drug administration can lead to substantial decreases in malaria incidence, but for elimination within the next 40 years, transmission reduction in both Zanzibar and mainland Tanzania is necessary., (© 2023. The Author(s).)
- Published
- 2023
- Full Text
- View/download PDF
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.