37 results on '"Chitnis, Nakul"'
Search Results
2. Correction: Testing and treatment for malaria elimination: a systematic review
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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.
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- 2024
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3. Testing and treatment for malaria elimination: a systematic review
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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.
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- 2023
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4. Leveraging mathematical models of disease dynamics and machine learning to improve development of novel malaria interventions
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Golumbeanu, Monica, Yang, Guo-Jing, Camponovo, Flavia, Stuckey, Erin M., Hamon, Nicholas, Mondy, Mathias, Rees, Sarah, Chitnis, Nakul, Cameron, Ewan, and Penny, Melissa A.
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- 2022
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5. Predicting the impact of outdoor vector control interventions on malaria transmission intensity from semi-field studies
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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
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- 2021
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6. Evaluation of different deployment strategies for larviciding to control malaria: a simulation study
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Runge, Manuela, Mapua, Salum, Nambunga, Ismail, Smith, Thomas A., Chitnis, Nakul, Okumu, Fredros, and Pothin, Emilie
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- 2021
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7. Incidence and consequences of damage to insecticide-treated mosquito nets in Kenya
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Smith, Thomas, Denz, Adrian, Ombok, Maurice, Bayoh, Nabie, Koenker, Hannah, Chitnis, Nakul, Briet, Olivier, Yukich, Joshua, and Gimnig, John E.
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- 2021
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8. Correction to: Evaluation of different deployment strategies for larviciding to control malaria: a simulation study
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Runge, Manuela, Mapua, Salum, Nambunga, Ismail, Smith, Thomas A., Chitnis, Nakul, Okumu, Fredros, and Pothin, Emilie
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- 2021
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9. The development and evaluation of a self-marking unit to estimate malaria vector survival and dispersal distance
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Saddler, Adam, Kreppel, Katharina S., Chitnis, Nakul, Smith, Thomas A., Denz, Adrian, Moore, Jason D., Tambwe, Mgeni M., and Moore, Sarah J.
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- 2019
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10. Resurgence of malaria infection after mass treatment: a simulation study
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Smith, Thomas A., Pemberton-Ross, Peter, Penny, Melissa A., and Chitnis, Nakul
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- 2019
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11. Theory of reactive interventions in the elimination and control of malaria
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Chitnis, Nakul, Pemberton-Ross, Peter, Yukich, Josh, Hamainza, Busiku, Miller, John, Reiker, Theresa, Eisele, Thomas P., and Smith, Thomas A.
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- 2019
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12. Models of effectiveness of interventions against malaria transmitted by Anopheles albimanus
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Briët, Olivier J. T., Impoinvil, Daniel E., Chitnis, Nakul, Pothin, Emilie, Lemoine, Jean Frantz, Frederic, Joseph, and Smith, Thomas A.
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- 2019
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13. Modelling reactive case detection strategies for interrupting transmission of Plasmodium falciparum malaria
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Reiker, Theresa, Chitnis, Nakul, and Smith, Thomas
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- 2019
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14. Modelling the impact of insecticide-based control interventions on the evolution of insecticide resistance and disease transmission
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Barbosa, Susana, Kay, Katherine, Chitnis, Nakul, and Hastings, Ian M.
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- 2018
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15. Potential causes and consequences of behavioural resilience and resistance in malaria vector populations: a mathematical modelling analysis
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Killeen, Gerry and Chitnis, Nakul
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qx_650 ,parasitic diseases ,qu_26.5 ,qx_600 ,wa_240 ,wa_110 - Abstract
Background\ud \ud The ability of mosquitoes to evade fatal exposure to insecticidal nets and sprays represents the primary obstacle to eliminating malaria. However, it remains unclear which behaviours are most important for buffering mosquito and parasite populations against vector control.\ud \ud Methods\ud \ud Simulated life histories were used to compare the impact of alternative feeding behaviour strategies upon overall lifetime feeding success, and upon temporal distributions of successful feeds and biting rates experienced by unprotected humans, in the presence and absence of insecticidal nets. Strictly nocturnal preferred feeding times were contrasted with 1) a wider preference window extending to dawn and dusk, and 2) crepuscular preferences wherein foraging is suppressed when humans sleep and can use nets but is maximal immediately before and after. Simulations with diversion and mortality parameters typical of endophagic, endophilic African vectors, such as Anopheles gambiae and Anopheles funestus, were compared with those for endophagic but exophilic species, such as Anopheles arabiensis, that also enter houses but leave earlier before lethal exposure to insecticide-treated surfaces occurs.\ud \ud Results\ud \ud Insecticidal nets were predicted to redistribute successful feeding events to dawn and dusk where these were included in the profile of innately preferred feeding times. However, predicted distributions of biting unprotected humans were unaffected because extended host-seeking activity was redistributed to innately preferred feeding times. Recently observed alterations of biting activity distributions therefore reflect processes not captured in this model, such as evolutionary selection of heritably modified feeding time preferences or phenotypically plastic expression of feeding time preference caused by associative learning. Surprisingly, endophagy combined with exophily, among mosquitoes that enter houses but then feed and/or rest briefly before rapidly exiting, consistently attenuated predicted insecticide impact more than any feeding time preference trait.\ud \ud Conclusions\ud \ud Regardless of underlying cause, recent redistributions of host-biting activity to dawn and dusk necessitate new outdoor control strategies. However, persistently indoor-feeding vectors, that evade intradomiciliary insecticide exposure, are at least equally important. Fortunately, recent evaluations of occupied houses or odour-baited stations, with baffled entrances that retain An. arabiensis within insecticide-treated structures, illustrate how endophagic but exophilic vectors may be more effectively tackled using existing insecticides.
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- 2014
16. Modelling the implications of stopping vector control for malaria control and elimination.
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Yukich, Joshua O. and Chitnis, Nakul
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MALARIA prevention , *DISEASE vectors , *PLASMODIUM falciparum , *EPIDEMIOLOGY , *MATHEMATICAL models , *REGRESSION analysis - Abstract
Background: Increasing coverage of malaria vector control interventions globally has led to significant reductions in disease burden. However due to its high recurrent cost, there is a need to determine if and when vector control can be safely scaled back after transmission has been reduced. Methods and findings: A mathematical model of Plasmodium falciparum malaria epidemiology was simulated to determine the impact of scaling back vector control on transmission and disease. A regression analysis of simulation results was conducted to derive predicted probabilities of resurgence, severity of resurgence and time to resurgence under various settings. Results indicate that, in the absence of secular changes in transmission, there are few scenarios where vector control can be removed without high expectation of resurgence. These, potentially safe, scenarios are characterized by low historic entomological inoculation rates, successful vector control programmes that achieve elimination or near elimination, and effective surveillance systems with high coverage and effective treatment of malaria cases. Conclusions: Programmes and funding agencies considering scaling back or withdrawing vector control from previously malaria endemic areas need to first carefully consider current receptivity and other available interventions in a risk assessment. Surveillance for resurgence needs to be continuously conducted over a long period of time in order to ensure a rapid response should vector control be withdrawn. [ABSTRACT FROM AUTHOR]
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- 2017
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17. A stochastic model for the probability of malaria extinction by mass drug administration.
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Pemberton-Ross, Peter, Chitnis, Nakul, Pothin, Emilie, and Smith, Thomas A.
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MALARIA prevention , *DRUG administration , *STOCHASTIC analysis , *DISTRIBUTION (Probability theory) , *MATHEMATICAL functions - Abstract
Background: Mass drug administration (MDA) has been proposed as an intervention to achieve local extinction of malaria. Although its effect on the reproduction number is short lived, extinction may subsequently occur in a small population due to stochastic fluctuations. This paper examines how the probability of stochastic extinction depends on population size, MDA coverage and the reproduction number under control, Rc. A simple compartmental model is developed which is used to compute the probability of extinction using probability generating functions. The expected time to extinction in small populations after MDA for various scenarios in this model is calculated analytically. The results indicate that mass drug administration (Firstly, Rc must be sustained at Rc < 1.2 to avoid the rapid re-establishment of infections in the population. Secondly, the MDA must produce effective cure rates of >95% to have a non-negligible probability of successful elimination. Stochastic fluctuations only significantly affect the probability of extinction in populations of about 1000 individuals or less. The expected time to extinction via stochastic fluctuation is less than 10 years only in populations less than about 150 individuals. Clustering of secondary infections and of MDA distribution both contribute positively to the potential probability of success, indicating that MDA would most effectively be administered at the household level. Conclusions: There are very limited circumstances in which MDA will lead to local malaria elimination with a substantial probability. [ABSTRACT FROM AUTHOR]
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- 2017
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18. Estimation of malaria parasite reservoir coverage using reactive case detection and active community fever screening from census data with rapid diagnostic tests in southern Zambia: a re-sampling approach.
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Yukich, Joshua, Bennett, Adam, Yukich, Rudy, Stuck, Logan, Hamainza, Busiku, Silumbe, Kafula, Smith, Tom, Chitnis, Nakul, Steketee, Richard W., Finn, Timothy, Eisele, Thomas P., and Miller, John M.
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MALARIA diagnosis ,PLASMODIUM ,MEDICAL screening ,DRUG administration ,MALARIA prevention ,PUBLIC health - Abstract
Background and methods: In areas where malaria transmission has been suppressed by vector control interventions many malaria control and elimination programmes are actively seeking new interventions to further reduce malaria prevalence, incidence and transmission. Malaria infection prevalence and incidence has been shown to cluster geographically, especially at lower transmission levels, and as such a reactive strategy is frequently used, by which index cases presenting to a passive surveillance system are used to target small areas for testing and treatment, reactive case detection (RCD), or focal drug administration (fDA). This study utilizes geo-located data from a census with parasitological testing with rapid diagnostic tests (RDTs) and treatment-seeking data collection conducted in southern Zambia to estimate the coverage of RCD or fDA in terms of the population and parasite reservoir as well as the operational requirements of such strategies, using a re-sampling algorithm developed exclusively for this purpose. This re-sampling algorithm allows for the specification of several parameters, such that different operational variants of these reactive strategies can be examined, including varying the search radius, screening for fever, or presumptive treatment (fDA). Results: Results indicate that RCD, fDA and active fever screening followed by RCD, even with search radii over several hundered meters will only yield limited coverage of the RDT positive parasite reservoir during a short period. Long-term use of these strategies may increase this proportion. Reactive strategies detect a higher proportion of the reservoir of infections than random searches, but this effect appears to be greater in areas of low, but not moderate malaria prevalence in southern Zambia. Discussion: Increases in the sensitivity of RDTs could also affect these results. The number of individuals and households that need to be searched increase rapidly, but approximately linearly with search radius. Conclusions: Reactive strategies in southern Zambia yield improved identification of the parasite reservoir when targeted to areas with prevalence less than 10%. The operational requirements of delivering reactive strategies routinely are likely to prevent their uptake until prevalence falls far below this level. [ABSTRACT FROM AUTHOR]
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- 2017
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19. 'Nature or nurture': survival rate, oviposition interval, and possible gonotrophic discordance among South East Asian anophelines.
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Charlwood, J. Derek, Nenhep, Somalay, Sovannaroth, Siv, Morgan, John C., Hemingway, Janet, Chitnis, Nakul, and Briët, Olivier J. T.
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ANOPHELES ,SURVIVAL analysis (Biometry) ,OVIPARITY in insects ,PARITY (Obstetrics) ,MOSQUITO physiology ,BEHAVIOR - Abstract
Background: Mosquito survival, oviposition interval and gonotrophic concordance are important determinants of vectorial capacity. These may vary between species or within a single species depending on the environment. They may be estimated by examination of the ovaries of host-seeking mosquitoes. Methods: Landing collections, Furvela tent-trap and CDC light-trap collections were undertaken sequentially in four locations in Cambodia between February 2012 and December 2013 and samples from the collected mosquitoes were dissected to determine parity, sac stage (indicative of time spent prior to returning to feed) and egg stage. Results: A total of 27,876 Anopheles from 15 species or species groups were collected in the four locations and 2883 specimens were dissected. Both the density and predominant species collected varied according to location and trapping method. Five species were dissected in sufficient numbers to allow comparisons between locations. Estimated oviposition interval differed markedly between species but less within species among different locations. Anopheles aconitus had the shortest cycle, which was 3.17 days (95 % CI 3-3.64), and Anopheles barbirostris had the longest cycle, which took four days (95 % CI 3.29-4). Anopheles minimus had a higher sac rate in weeks leading up to a full moon but there was apparently little effect of moon phase on Anopheles dirus. Despite the fact that many of the species occurred at very low densities, there was no evidence of gonotrophic dissociation in any of them, even during sustained hot, dry periods. The principal Cambodian malaria vector, An. dirus, was only common in one location where it was collected in miniature light-traps inside houses. It did not appear to have an exceptional survival rate (as judged by the low average parous rate) or oviposition cycle. Conclusions: Differences in the oviposition interval were more pronounced among species within locations than within species among ecologically diverse locations. A nationwide survey using CDC light-traps for the collection of An. dirus inside houses may help in determining patterns of malaria transmission in Cambodia. [ABSTRACT FROM AUTHOR]
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- 2016
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20. Operational strategies of anti-malarial drug campaigns for malaria elimination in Zambia's southern province: a simulation study.
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Stuckey, Erin M., Miller, John M., Littrell, Megan, Chitnis, Nakul, and Steketee, Rick
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ANTIMALARIALS ,INSECTICIDE-treated mosquito nets ,PLASMODIUM falciparum ,DRUG administration ,IVERMECTIN - Abstract
Background: Malaria elimination requires reducing both the potential of mosquitoes to transmit parasites to humans and humans to transmit parasites to mosquitoes. To achieve this goal in Southern province, Zambia a mass test and treat (MTAT) campaign was conducted from 2011-2013 to complement high coverage of long-lasting insecticide-treated nets (LLIN). To identify factors likely to increase campaign effectiveness, a modelling approach was applied to investigate the simulated effect of alternative operational strategies for parasite clearance in southern province. Methods: OpenMalaria, a discrete-time, individual-based stochastic model of malaria, was parameterized for the study area to simulate anti-malarial drug administration for interruption of transmission. Simulations were run for scenarios with a range of artemisinin-combination therapies, proportion of the population reached by the campaign, targeted age groups, time between campaign rounds, Plasmodium falciparum test protocols, and the addition of drugs aimed at preventing onward transmission. A sensitivity analysis was conducted to assess uncertainty of simulation results. Scenarios were evaluated based on the reduction in all-age parasite prevalence during the peak transmission month one year following the campaign, compared to the currently-implemented strategy of MTAT 19 % population coverage at pilot and 40 % coverage during the first year of implementation in the presence of 56 % LLIN use and 18 % indoor residual spray coverage. Results: Simulation results suggest the most important determinant of success in reducing prevalence is the population coverage achieved in the campaign, which would require more than 1 year of campaign implementation for elimination. The inclusion of single low-dose primaquine, which acts as a gametocytocide, or ivermectin, which acts as an endectocide, to the drug regimen did not further reduce parasite prevalence one year following the campaign compared to the currently-implemented strategy. Simulation results indicate a high proportion of low-density infections were missed by rapid diagnostic tests that would be treated and cleared with mass drug administration (MDA). Conclusions: The optimal implementation strategy for MTAT or MDA will vary by background level of prevalence, by rate of infections imported to the area, and by ability to operationally achieve high population coverage. Overall success with new parasite clearance strategies depends on continued coverage of vector control interventions to ensure sustained gains in reduction of disease burden. [ABSTRACT FROM AUTHOR]
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- 2016
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21. Comparative assessment of diverse strategies for malaria vector population control based on measured rates at which mosquitoes utilize targeted resource subsets.
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Killeen, Gerry F., Kiware, Samson S., Seyoum, Aklilu, Gimnig, John E., Corliss, George F., Stevenson, Jennifer, Drakeley, Christopher J., and Chitnis, Nakul
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MOSQUITO vectors ,MALARIA prevention ,MOSQUITO control ,PLASMODIUM ,INSECTICIDE-treated mosquito nets - Abstract
Background: Eliminating malaria requires vector control interventions that dramatically reduce adult mosquito population densities and survival rates. Indoor applications of insecticidal nets and sprays are effective against an important minority of mosquito species that rely heavily upon human blood and habitations for survival. However, complementary approaches are needed to tackle a broader diversity of less human-specialized vectors by killing them at other resource targets. Methods: Impacts of strategies that target insecticides to humans or animals can be rationalized in terms of biological coverage of blood resources, quantified as proportional coverage of all blood resources mosquito vectors utilize. Here, this concept is adapted to enable impact prediction for diverse vector control strategies based on measurements of utilization rates for any definable, targetable resource subset, even if that overall resource is not quantifiable. Results: The usefulness of this approach is illustrated by deriving utilization rate estimates for various blood, resting site, and sugar resource subsets from existing entomological survey data. Reported impacts of insecticidal nets upon human-feeding vectors, and insecticide-treated livestock upon animal-feeding vectors, are approximately consistent with model predictions based on measured utilization rates for those human and animal blood resource subsets. Utilization rates for artificial sugar baits compare well with blood resources, and are consistent with observed impact when insecticide is added. While existing data was used to indirectly measure utilization rates for a variety of resting site subsets, by comparison with measured rates of blood resource utilization in the same settings, current techniques for capturing resting mosquitoes underestimate this quantity, and reliance upon complex models with numerous input parameters may limit the applicability of this approach. Conclusions: While blood and sugar consumption can be readily quantified using existing methods for detecting natural markers or artificial tracers, improved techniques for labelling mosquitoes, or other arthropod pathogen vectors, will be required to assess vector control measures which target them when they utilize non-nutritional resources such as resting, oviposition, and mating sites. [ABSTRACT FROM AUTHOR]
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- 2014
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22. Made-to-measure malaria vector control strategies: rational design based on insecticide properties and coverage of blood resources for mosquitoes.
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Killeen, Gerry F., Seyoum, Aklilu, Gimnig, John E., Stevenson, Jennifer C., Drakeley, Christopher J., and Chitnis, Nakul
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MALARIA transmission ,PLASMODIUM falciparum ,INSECTICIDES ,MOSQUITO vectors ,VECTOR control ,LIVESTOCK - Abstract
Eliminating malaria from highly endemic settings will require unprecedented levels of vector control. To suppress mosquito populations, vector control products targeting their blood hosts must attain high biological coverage of all available sources, rather than merely high demographic coverage of a targeted resource subset, such as humans while asleep indoors. Beyond defining biological coverage in a measurable way, the proportion of blood meals obtained from humans and the proportion of bites upon unprotected humans occurring indoors also suggest optimal target product profiles for delivering insecticides to humans or livestock. For vectors that feed only occasionally upon humans, preferred animal hosts may be optimal targets for mosquito-toxic insecticides, and vapour-phase insecticides optimized to maximize repellency, rather than toxicity, may be ideal for directly protecting people against indoor and outdoor exposure. However, for vectors that primarily feed upon people, repellent vapour-phase insecticides may be inferior to toxic ones and may undermine the impact of contact insecticides applied to human sleeping spaces, houses or clothing if combined in the same time and place. These concepts are also applicable to other mosquito-borne anthroponoses so that diverse target species could be simultaneously controlled with integrated vector management programmes. Measurements of these two crucial mosquito behavioural parameters should now be integrated into programmatically funded, longitudinal, national-scale entomological monitoring systems to inform selection of available technologies and investment in developing new ones. [ABSTRACT FROM AUTHOR]
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- 2014
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23. Effects of changing mosquito host searching behaviour on the cost effectiveness of a mass distribution of long-lasting, insecticidal nets: a modelling study.
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Briët, Olivier J. T. and Chitnis, Nakul
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MALARIA prevention equipment , *MOSQUITO vectors , *COST effectiveness , *INSECT bites & stings , *PLASMODIUM falciparum , *PYRETHROIDS - Abstract
Background: The effectiveness of long-lasting, insecticidal nets (LLINs) in preventing malaria is threatened by the changing biting behaviour of mosquitoes, from nocturnal and endophagic to crepuscular and exophagic, and by their increasing resistance to insecticides. Methods: Using epidemiological stochastic simulation models, we studied the impact of a mass LLIN distribution on Plasmodium falciparum malaria. Specifically, we looked at impact in terms of episodes prevented during the effective life of the batch and in terms of net health benefits (NHB) expressed in disability adjusted life years (DALYs) averted, depending on biting behaviour, resistance (as measured in experimental hut studies), and on pre-intervention transmission levels. Results: Results were very sensitive to assumptions about the probabilistic nature of host searching behaviour. With a shift towards crepuscular biting, under the assumption that individual mosquitoes repeat their behaviour each gonotrophic cycle, LLIN effectiveness was far less than when individual mosquitoes were assumed to vary their behaviour between gonotrophic cycles. LLIN effectiveness was equally sensitive to variations in host-searching behaviour (if repeated) and to variations in resistance. LLIN effectiveness was most sensitive to pre-intervention transmission level, with LLINs being least effective at both very low and very high transmission levels, and most effective at around four infectious bites per adult per year. A single LLIN distribution round remained cost effective, except in transmission settings with a pre-intervention inoculation rate of over 128 bites per year and with resistant mosquitoes that displayed a high proportion (over 40%) of determined crepuscular host searching, where some model variants showed negative NHB. Conclusions: Shifts towards crepuscular host searching behaviour can be as important in reducing LLIN effectiveness and cost effectiveness as resistance to pyrethroids. As resistance to insecticides is likely to slow down the development of behavioural resistance and vice versa, the two types of resistance are unlikely to occur within the same mosquito population. LLINs are likely cost effective interventions against malaria, even in areas with strong resistance to pyrethroids or where a large proportion of host-mosquito contact occurs during times when LLIN users are not under their nets. [ABSTRACT FROM AUTHOR]
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- 2013
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24. Effects of pyrethroid resistance on the cost effectiveness of a mass distribution of longlasting insecticidal nets: a modelling study.
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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
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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]
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- 2013
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25. Modelling the cost-effectiveness of mass screening and treatment for reducing Plasmodium falciparum malaria burden.
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Crowell, Valerie, Briët, Olivier J. T., Hardy, Diggory, Chitnis, Nakul, Maire, Nicolas, Di Pasquale, Aurelio, and Smith, Thomas A.
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MEDICAL screening ,PLASMODIUM falciparum ,COST effectiveness ,ENTOMOLOGY research ,MALARIA - Abstract
Background: Past experience and modelling suggest that, in most cases, mass treatment strategies are not likely to succeed in interrupting Plasmodium falciparum malaria transmission. However, this does not preclude their use to reduce disease burden. Mass screening and treatment (MSAT) is preferred to mass drug administration (MDA), as the latter involves massive over-use of drugs. This paper reports simulations of the incremental cost-effectiveness of well-conducted MSAT campaigns as a strategy for P. falciparum malaria disease-burden reduction in settings with varying receptivity (ability of the combined vector population in a setting to transmit disease) and access to case management. Methods: MSAT incremental cost-effectiveness ratios (ICERs) were estimated in different sub-Saharan African settings using simulation models of the dynamics of malaria and a literature-based MSAT cost estimate. Imported infections were simulated at a rate of two per 1,000 population per annum. These estimates were compared to the ICERs of scaling up case management or insecticide-treated net (ITN) coverage in each baseline health system, in the absence of MSAT. Results: MSAT averted most episodes, and resulted in the lowest ICERs, in settings with a moderate level of disease burden. At a low preintervention entomological inoculation rate (EIR) of two infectious bites per adult per annum (IBPAPA) MSAT was never more cost-effective than scaling up ITNs or case management coverage. However, at pre-intervention entomological inoculation rates (EIRs) of 20 and 50 IBPAPA and ITN coverage levels of 40 or 60%, respectively, the ICER of MSAT was similar to that of scaling up ITN coverage further. Conclusions: In all the transmission settings considered, achieving a minimal level of ITN coverage is a "best buy". At low transmission, MSAT probably is not worth considering. Instead, MSAT may be suitable at medium to high levels of transmission and at moderate ITN coverage. If undertaken as a burden-reducing intervention, MSAT should be continued indefinitely and should complement, not replace, case management and vector control interventions. [ABSTRACT FROM AUTHOR]
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- 2013
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26. Simulation of malaria epidemiology and control in the highlands of western Kenya.
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Stuckey, Erin M., Stevenson, Jennifer C., Cooke, Mary K., Owaga, Chrispin, Marube, Elizabeth, Oando, George, Hardy, Diggory, Drakeley, Chris, Smith, Thomas A., Cox, Jonathan, and Chitnis, Nakul
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MALARIA ,PUBLIC health ,PLASMODIUM falciparum ,DECISION making - Abstract
Background: Models of Plasmodium falciparum malaria epidemiology that provide realistic quantitative predictions of likely epidemiological outcomes of existing vector control strategies have the potential to assist in planning for the control and elimination of malaria. This work investigates the applicability of mathematical modelling of malaria transmission dynamics in Rachuonyo South, a district with low, unstable transmission in the highlands of western Kenya. Methods: Individual-based stochastic simulation models of malaria in humans and a deterministic model of malaria in mosquitoes as part of the OpenMalaria platform were parameterized to create a scenario for the study area based on data from ongoing field studies and available literature. The scenario was simulated for a period of two years with a population of 10,000 individuals and validated against malaria survey data from Rachuonyo South. Simulations were repeated with multiple random seeds and an ensemble of 14 model variants to address stochasticity and model uncertainty. A one-dimensional sensitivity analysis was conducted to address parameter uncertainty. Results: The scenario was able to reproduce the seasonal pattern of the entomological inoculation rate (EIR) and patent infections observed in an all-age cohort of individuals sampled monthly for one year. Using an EIR estimated from serology to parameterize the scenario resulted in a closer fit to parasite prevalence than an EIR estimated using entomological methods. The scenario parameterization was most sensitive to changes in the timing and effectiveness of indoor residual spraying (IRS) and the method used to detect P. falciparum in humans. It was less sensitive than expected to changes in vector biting behaviour and climatic patterns. Conclusions: The OpenMalaria model of P. falciparum transmission can be used to simulate the impact of different combinations of current and potential control interventions to help plan malaria control in this low transmission setting. In this setting and for these scenarios, results were highly sensitive to transmission, vector exophagy, exophily and susceptibility to IRS, and the detection method used for surveillance. The level of accuracy of the results will thus depend upon the precision of estimates for each. New methods for analysing and evaluating uncertainty in simulation results will enhance the usefulness of simulations for malaria control decision-making. Improved measurement tools and increased primary data collection will enhance model parameterization and epidemiological monitoring. Further research is needed on the relationship between malaria indices to identify the best way to quantify transmission in low transmission settings. Measuring EIR through mosquito collection may not be the optimal way to estimate transmission intensity in areas with low, unstable transmission. [ABSTRACT FROM AUTHOR]
- Published
- 2012
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27. Measurement of overall insecticidal effects in experimental hut trials.
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Briët, Olivier JT, Smith, Thomas A, and Chitnis, Nakul
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PUBLIC health ,MOSQUITOES ,DIPTERA ,MORTALITY ,DEATH (Biology) ,COMMUNICABLE diseases ,HUMAN services ,HEALTH & welfare funds - Abstract
Background: The 'overall insecticidal effect' is a key measure used to evaluate public health pesticides for indoor use in experimental hut trials. It depends on the proportion of mosquitoes that are killed out of those that enter the treated hut, intrinsic mortality in the control hut, and the ratio of mosquitoes entering the treatment hut to those entering the control hut. This paper critically examines the way the effect is defined, and discusses how it can be used to infer effectiveness of intervention programmes. Findings: The overall insecticidal effect, as defined by the World Health Organization in 2006, can be negative when deterrence from entering the treated hut is high, even if all mosquitoes that enter are killed, wrongly suggesting that the insecticide enhances mosquito survival. Also in the absence of deterrence, even if the insecticide kills all mosquitoes in the treatment hut, the insecticidal effect is less than 100%, unless intrinsic mortality is nil. A proposed alternative definition for the measurement of the overall insecticidal effect has the desirable range of 0 to 1 (100%), provided mortality among non-repelled mosquitoes in the treated hut is less than the corresponding mortality in the control hut. This definition can be built upon to formulate the coverage-dependent insecticidal effectiveness of an intervention programme. Coverage-dependent population protection against feeding can be formulated similarly. Conclusions: This paper shows that the 2006 recommended quantity for measuring the overall insecticidal effect is problematic, and proposes an alternative quantity with more desirable properties. [ABSTRACT FROM AUTHOR]
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- 2012
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28. Potential causes and consequences of behavioural resilience and resistance in malaria vector populations : a mathematical modelling analysis
- Author
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Killeen, Gerry F. and Chitnis, Nakul
- Subjects
2. Zero hunger ,3. Good health
29. Modelling the impact of insecticide-based control interventions on the evolution of insecticide resistance and disease transmission
- Author
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Barbosa, Susana, Kay, Katherine, Chitnis, Nakul, and Hastings, Ian M.
- Subjects
3. Good health
30. Does mosquito mortality in WHO insecticide susceptibility tests relate to mosquito mortality in LLIN experimental hut studies?
- Author
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Briët, Olivier J. T., Chitnis, Nakul, and Penny, Melissa
- Subjects
- *
MOSQUITOES - Abstract
An abstract of the article "Does mosquito mortality in WHO insecticide susceptibility tests relate to mosquito mortality in LLIN experimental hut studies?," by Olivier J. T. Briët, Nakul Chitnis, and Melissa Penny is presented.
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- 2012
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31. Modeling the effects of vector control interventions in reducing malaria transmission, morbidity and mortality.
- Author
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Chitnis, Nakul, Hardy, Diggory, Gnaegi, Guillaume, Boutsika, Konstantina, Maire, Nicolas, Steketee, Richard, Schapira, Allan, and Smith, Tom
- Subjects
- *
MALARIA , *VECTOR control - Abstract
An abstract of the article "Modeling the effects of vector control interventions in reducing malaria transmission, morbidity and mortality" that was presented at a conference titled "From Parasite to Prevention: Advances in the understanding of malaria" held in Edinburgh, Great Britain on October 20-22, 2010, is presented.
- Published
- 2010
- Full Text
- View/download PDF
32. Modeling the trade-off between effective case management and imported malaria cases in different settings of P. falciparum malaria transmission intensity.
- Author
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Crowell, Valerie, Hardy, Diggory, Chitnis, Nakul, Maire, Nicolas, and Smith, Thomas
- Subjects
MALARIA ,INFECTIOUS disease transmission - Abstract
An abstract of the article "Modeling the trade-off between effective case management and imported malaria cases in different settings of P. falciparum malaria transmission intensity" that was presented at a conference titled "From Parasite to Prevention: Advances in the understanding of malaria" held in Edinburgh, Great Britain on October 20-22, 2010, is presented.
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- 2010
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- View/download PDF
33. Modelling the requirements and benefits of mosquito control interventions in the presence of mosquito dispersal.
- Author
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Lutambi, Angelina M., Chitnis, Nakul, Smith, Tom, and Penny, Melissa
- Subjects
- *
MOSQUITO control , *MOSQUITO vectors - Abstract
An abstract of the article "Modelling the requirements and benefits of mosquito control interventions in the presence of mosquito dispersal," by Angelina M Lutambi, Nakul Chitnis, Tom Smith, and Melissa Penny is presented.
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- 2012
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- View/download PDF
34. Modeling the cost-effectiveness of mass screening and treatment for reducing Plasmodium falciparum malaria burden.
- Author
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Crowell, Valerie, Briëf, Olivier J. T., Hardy, Diggory, Chitnis, Nakul, Maire, Nicolas, Pasguale, Aurelio Di, and Smith, Thomas A.
- Subjects
MALARIA ,PLASMODIUM falciparum - Abstract
An abstract of the article "Modeling the cost-effectiveness of mass screening and treatment for reducing Plasmodium falciparum malaria burden," by Valerie Crowell, Olivier J. T. Briëf, Diggory Hardy, Nakul Chitnis, Nicolas Maire, Aurelio Di Pasguale, and Thomas A. Smith is presented.
- Published
- 2012
- Full Text
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35. 'Nature or nurture': survival rate, oviposition interval, and possible gonotrophic discordance among South East Asian anophelines.
- Author
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Derek Charlwood J, Nenhep S, Sovannaroth S, Morgan JC, Hemingway J, Chitnis N, and Briët OJ
- Subjects
- Animals, Cambodia, Female, Survival Rate, Anopheles physiology, Feeding Behavior, Mosquito Vectors physiology, Oviposition
- Abstract
Background: Mosquito survival, oviposition interval and gonotrophic concordance are important determinants of vectorial capacity. These may vary between species or within a single species depending on the environment. They may be estimated by examination of the ovaries of host-seeking mosquitoes., Methods: Landing collections, Furvela tent-trap and CDC light-trap collections were undertaken sequentially in four locations in Cambodia between February 2012 and December 2013 and samples from the collected mosquitoes were dissected to determine parity, sac stage (indicative of time spent prior to returning to feed) and egg stage., Results: A total of 27,876 Anopheles from 15 species or species groups were collected in the four locations and 2883 specimens were dissected. Both the density and predominant species collected varied according to location and trapping method. Five species were dissected in sufficient numbers to allow comparisons between locations. Estimated oviposition interval differed markedly between species but less within species among different locations. Anopheles aconitus had the shortest cycle, which was 3.17 days (95 % CI 3-3.64), and Anopheles barbirostris had the longest cycle, which took four days (95 % CI 3.29-4). Anopheles minimus had a higher sac rate in weeks leading up to a full moon but there was apparently little effect of moon phase on Anopheles dirus. Despite the fact that many of the species occurred at very low densities, there was no evidence of gonotrophic dissociation in any of them, even during sustained hot, dry periods. The principal Cambodian malaria vector, An. dirus, was only common in one location where it was collected in miniature light-traps inside houses. It did not appear to have an exceptional survival rate (as judged by the low average parous rate) or oviposition cycle., Conclusions: Differences in the oviposition interval were more pronounced among species within locations than within species among ecologically diverse locations. A nationwide survey using CDC light-traps for the collection of An. dirus inside houses may help in determining patterns of malaria transmission in Cambodia.
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- 2016
- Full Text
- View/download PDF
36. Effects of pyrethroid resistance on the cost effectiveness of a mass distribution of long-lasting insecticidal nets: a modelling study.
- Author
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Briët OJ, Penny MA, Hardy D, Awolola TS, Van Bortel W, Corbel V, Dabiré RK, Etang J, Koudou BG, Tungu PK, and Chitnis N
- Subjects
- Animals, Computer Simulation, Cost-Benefit Analysis, Female, Humans, Insecticide-Treated Bednets supply & distribution, Piperonyl Butoxide pharmacology, Anopheles drug effects, Insecticide Resistance, Insecticide-Treated Bednets economics, Insecticides pharmacology, Mosquito Control economics, Mosquito Control methods, Pyrethrins pharmacology
- 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 OpenMalaria, 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 pyrethroid-piperonyl 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.
- Published
- 2013
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37. Target product profile choices for intra-domiciliary malaria vector control pesticide products: repel or kill?
- Author
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Killeen GF, Chitnis N, Moore SJ, and Okumu FO
- Subjects
- Animals, Humans, Models, Statistical, Insect Repellents pharmacology, Insecticides pharmacology, Malaria prevention & control, Mosquito Control methods
- Abstract
Background: The most common pesticide products for controlling malaria-transmitting mosquitoes combine two distinct modes of action: 1) conventional insecticidal activity which kills mosquitoes exposed to the pesticide and 2) deterrence of mosquitoes away from protected humans. While deterrence enhances personal or household protection of long-lasting insecticidal nets and indoor residual sprays, it may also attenuate or even reverse communal protection if it diverts mosquitoes to non-users rather than killing them outright., Methods: A process-explicit model of malaria transmission is described which captures the sequential interaction between deterrent and toxic actions of vector control pesticides and accounts for the distinctive impacts of toxic activities which kill mosquitoes before or after they have fed upon the occupant of a covered house or sleeping space., Results: Increasing deterrency increases personal protection but consistently reduces communal protection because deterrent sub-lethal exposure inevitably reduces the proportion subsequently exposed to higher lethal doses. If the high coverage targets of the World Health Organization are achieved, purely toxic products with no deterrence are predicted to generally provide superior protection to non-users and even users, especially where vectors feed exclusively on humans and a substantial amount of transmission occurs outdoors. Remarkably, this is even the case if that product confers no personal protection and only kills mosquitoes after they have fed., Conclusions: Products with purely mosquito-toxic profiles may, therefore, be preferable for programmes with universal coverage targets, rather than those with equivalent toxicity but which also have higher deterrence. However, if purely mosquito-toxic products confer little personal protection because they do not deter mosquitoes and only kill them after they have fed, then they will require aggressive "catch up" campaigns, with behaviour change communication strategies that emphasize the communal nature of protection, to achieve high coverage rapidly.
- Published
- 2011
- Full Text
- View/download PDF
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