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Rocky Mountain spotted fever (RMSF) is a severe tickborne disease that can reach epidemic proportions in communities with certain social and ecologic risk factors. In some areas, the case-fatality rate of brown dog tick-associated RMSF is up to 50%. Because of the spread of brown dog tick-associated RMSF in the southwestern United States and northern Mexico, the disease has the potential to emerge and become endemic in other communities that have large populations of free-roaming dogs, brown dog ticks, limited resources, and low provider awareness of the disease. By using a One Health approach, interdisciplinary teams can identify communities at risk and prevent severe or fatal RMSF in humans before cases occur. We have developed a conceptual framework for RMSF prevention to enable communities to identify their RMSF risk level and implement prevention and control strategies.

A total of 2,504 ticks of 5 species (Ixodes scapularis, Dermacentor variabilis, Amblyomma americanum, Haemaphysalis leporispalustris, and H. longicornis) were collected over 2 yr (2014-2015) in New York City parks. Specimens were collected via tick-dragging, identified to species, and tested for pathogens of human diseases. The causative agents of 5 human diseases (Lyme borreliosis, ehrlichiosis, babesiosis, anaplasmosis, and Rocky Mountain spotted fever) were detected in a subset of samples. Results of this surveillance effort further illustrate that risk of tick-borne disease is considerable even in parks located adjacent to densely populated areas., (Published by Oxford University Press on behalf of Entomological Society of America 2024.)

Due to climate change-induced alterations of temperature and humidity, the distribution of pathogen-carrying organisms such as ticks may shift. Tick survival is often limited by environmental factors such as dryness, but a predicted hotter and wetter world may allow the expansion of tick ranges. Dermacentor andersoni and D. variabilis ticks are morphologically similar, co-occur throughout the Inland Northwest of Washington State, U.S.A., and both can be injected with pathogenic Rickettsia and Francisella bacteria. Differences in behavior and the potential role of endosymbiotic Rickettsia and Francisella in these ticks are poorly studied. We wanted to measure behavioral and ecological differences between the two species and determine which, if any, Rickettsia and Francisella bacteria - pathogenic or endosymbiotic - they carried. Additionally, we wanted to determine if either tick species may be selected for if the climate in eastern Washington becomes wetter or dryer. We found that D. andersoni is more resistant to desiccation, but both species share similar questing behaviors such as climbing and attraction to bright light. Both also avoid the odor of eucalyptus and DEET but not permethrin. Although both tick species are capable of transmitting pathogenic species of Francisella and Rickettsia, which cause tularemia and Rocky Mountain Spotted Fever, respectively, we found primarily non-pathogenic endosymbiotic strains of Francisella and Rickettsia, and only one tick infected with F. tularensis subspecies holarctica., (© 2020 The Society for Vector Ecology.)

The invasive Asian longhorned tick, Haemaphysalis longicornis Neumann, was first detected in the United States in 2017. It has since been found in 12 states, and there is concern that the tick's parthenogenetic ability and wide variety of host species may allow for broader dissemination. Of the tick-borne diseases endemic to the United States, Rocky Mountain spotted fever (RMSF), a rapidly progressive and potentially fatal disease caused by Rickettsia rickettsii, is the most severe. There is considerable geographical overlap between spotted fever rickettsioses cases, which include RMSF, and the currently known distribution of H. longicornis, providing the potential for this tick to encounter this pathogen. We have evaluated the ability of H. longicornis to acquire and transmit R. rickettsii under laboratory conditions. Haemaphysalis longicornis as larvae and nymphs acquired the pathogen while feeding on infected guinea pigs. The infection persisted through every life stage, all of which were able to transmit R. rickettsii to naïve hosts. The pathogen was also transmitted at a low frequency between generations of H. longicornis through the ova. While H. longicornis was demonstrated to be a competent vector for R. rickettsii under laboratory conditions, the probability of its involvement in the maintenance and transmission of this pathogen in nature, as well as its potential impact on human health, requires further study., (Published by Oxford University Press on behalf of Entomological Society of America 2020.)

For the last decade, the New Jersey (NJ) Department of Health has reported between 42 and 144 new cases each year of "spotted fever group rickettsiosis" (SFGR), a statistic that reflects uncertainty regarding which rickettsial agents (Proteobacteria: Rickettsiaceae: Rickettsia ) are infecting NJ residents. To identify the Rickettsia circulating in NJ ticks, we used a combination of conventional and real time PCR approaches to screen 560 Dermacentor variabilis Say and 245 Amblyomma americanum L. obtained from a 1-day state-wide surveillance in May 2018 and an additional 394 D. variabilis collected across NJ in 2013-2018. We found zero D. variabilis infected with Rickettsia rickettsii, the agent of Rocky Mountain spotted fever and, on average, 1.3% infected with presumed nonpathogenic Rickettsia montanensis . We also found zero A. americanum infected with R. rickettsii, and 20% infected with Rickettsia amblyommatis, a prevalence somewhat lower than in more southern states. Overall, we conclude that it is unlikely that R. rickettsii vectored by D. variabilis is a primary cause of SFGR cases in NJ and discuss our findings in the context of known facts and current limitations. We conclude that understanding the causes of SFGR east of the Mississippi will require collaboration among medical doctors, public health authorities, and medical entomologists to follow up presumptive human cases of SFGR with detailed histories of exposure, species-specific molecular assays, and active surveillance of putative vectors and the pathogens they may carry.

Zoonoses are major causes of morbidity and mortality worldwide. Among them, Brazilian Spotted Fever (BSF) is an important one that occurs in some regions of South America and can be transmitted by the "star tick" Amblyomma sculptum. Application of acaricides against the larval stage is important as strategy of population control. However, there is still a deficiency of studies on chemical control of A. sculptum and the present work aims to evaluate the in vitro acaricidal activity of cypermethrin, flumethrin, deltamethrin, fipronil, coumaphos and chlorpyrifos against A. sculptum larvae. Bioassays were performed using the larval immersion test method. A discriminatory analysis between the antiparasitic classes most used for tick control was carried out, which made it possible to determine the classes with higher potential for controlling A. sculptum larvae. Our results showed that A. sculptum larvae present highest sensitivity to the synthetic pyrethroid group, followed by the phenylpyrazole, organophosphate and macrocyclic lactone groups. These findings may support studies on improvement of tick control as in animals as in the environment.

Brazilian spotted fever (BSF) is a highly lethal disease in southeastern Brazil. BSF is caused by the bacterium Rickettsia rickettsii and is transmitted by the bites of the tick of the genus Amblyomma. The spatial distribution of BSF risk areas is not well known in the country given the complexity of the transmission cycle. This study used the ecological niche modeling (ENM) approach to anticipate the potential distribution of the etiological agent (Rickettsia rickettsii), vectors (Amblyomma sculptum and A. dubitatum), and hosts (Hydrochoerus hydrochaeris, Didelphis aurita, and D. marsupialis) of BSF in Brazil. We compiled occurrence records for all vectors, hosts, and BSF from our own field surveillance, online repositories, and literature. ENM identified BSF risk areas in southeastern and southern Brazil, and anticipated other dispersed suitable areas in the western, central, and northeastern coast regions of Brazil. Tick vectors and mammalian hosts were confined to these same areas; however, host species showed broader suitability in northern Brazil. All species ENMs performed significantly better than random expectations. We also tested the BSF prediction based on 253 additional independent cases identified in our surveillance; the model anticipated 251 out of 253 of these independent cases. Background similarity tests comparing the ENMs of R. rickettsii, tick vectors, and mammalian hosts were unable to reject null hypotheses of niche similarity. Finally, we observed close coincidence between independent BSF cases, and areas suitable for combinations of vectors and hosts, reflecting the ability of these model pairs to anticipate the distribution of BSF cases across Brazil., (Copyright © 2020 Elsevier B.V. All rights reserved.)

An outbreak of Rocky Mountain spotted fever (RMSF) transmitted by the brown dog tick (Rhipicephalus sanguineus sensu lato) has emerged as a major human and animal health concern in Mexicali, Mexico. Due to high rates of brown dog tick infestation, susceptibility, and association with humans, dogs serve as sentinels and have a key role in the ecology of RMSF. A cross-sectional household questionnaire study was conducted in six rural and urban locations to characterize dog ecology and demography in RMSF high-and low-risk areas of Mexicali. In addition, we tracked movement patterns of 16 dogs using a GPS data logger. Of 253 households, 73% owned dogs, and dog ownership tended to be higher in high-risk areas, with a mean dog:human ratio of 0.43, compared with 0.3 in low-risk areas. Dogs in high-risk areas had higher fecundity and roamed more, but the dog density and numbers of free-roaming dogs were comparable. There was a higher proportion of younger dogs and lower proportion of older dogs in high-risk areas. The high proportion of immunologically naïve puppies in high risk areas could result in a lack of herd immunity leading to a more vulnerable dog and human population. The marked increase of space use of free-roaming dogs in high-risk areas suggests that unrestrained dogs could play an important role in spreading ticks and pathogens. As means to limit RMSF risk, practical changes could include increased efforts for spay-neuter and policies encouraging dog restraint to limit canine roaming and spread of ticks across communities; due to dog density is less impactful such policies may be more useful than restrictions on the number of owned dogs., Competing Interests: The authors have declared that no competing interests exist.

Although the ticks Amblyomma sculptum and Amblyomma aureolatum are important vectors of Rickettsia rickettsii, causative agent of the life-threatening Rocky Mountain spotted fever, A. aureolatum is considerably more susceptible to infection than A. sculptum. As the microbiota can interfere with the colonization of arthropod midgut (MG) by pathogens, in the current study we analyzed the MG microbiota of both tick species. Our results revealed that the MG of A. aureolatum harbors a prominent microbiota, while A. sculptum does not. Remarkably, a significant reduction of the bacterial load was recorded in R. rickettsii-infected A. aureolatum. In addition, the taxonomy analysis of the MG bacterial community of A. aureolatum revealed a dominance of the genus Francisella, suggesting an endosymbiosis. This study is the first step in getting insights into the mechanisms underlying the interactions among Amblyomma species, their microbiota and R. rickettsii. Additional studies to better understand these mechanisms are required and may help the development of novel alternatives to block rickettsial transmission., Competing Interests: Declaration of competing interest The author declares no conflicts of interest., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

It has been reported that starving ticks do not transmit spotted fever group Rickettsia immediately upon attachment because pathogenic bacteria exist in a dormant, uninfectious state and require time for 'reactivation' before transmission to a susceptible host. To clarify the length of reactivation period, we exposed guinea pigs to bites of Rickettsia rickettsii-infected Dermacentor variabilis (Say) and allowed ticks to remain attached for predetermined time periods from 0 to 48 h. Following removal of attached ticks, salivary glands were immediately tested by PCR, while guinea pigs were observed for 10-12 d post-exposure. Guinea pigs in a control group were subcutaneously inoculated with salivary glands from unfed D. variabilis from the same cohort. In a parallel experiment, skin at the location of tick bite was also excised at the time of tick removal to ascertain dissemination of pathogen from the inoculation site. Animals in every exposure group developed clinical and pathological signs of infection. The severity of rickettsial infection in animals increased with the length of tick attachment, but even attachments for less than 8 h resulted in clinically identifiable infection in some guinea pigs. Guinea pigs inoculated with salivary glands from unfed ticks also became severely ill. Results of our study indicate that R. rickettsii residing in salivary glands of unfed questing ticks does not necessarily require a period of reactivation to precede the salivary transmission and ticks can transmit infectious Rickettsia virtually as soon as they attach to the host., (Published by Oxford University Press on behalf of Entomological Society of America 2019.)

We report a fatal case of Rocky Mountain spotted fever (RMSF) in a man in Brazil without recent history of tick bites or environmental exposure. He received an accidental needlestick while working as a nurse. The nurse and his patient died. Both cases were confirmed as RMSF by molecular methods.

Introduction: Brazilian spotted fever (BSF), a lethal tick-borne Rickettsioses (2000 - 2018 >600 human deaths) involving synanthropic capybara as host., Methods: We introduced an alternative to mitigate human-capybara conflicts and epidemiologic concerns of BSF. Complex aspects like transmission dynamics, risk areas, host mobility, and birth rate control, were considered to develop a prevention strategy using an anti-GnRH vaccine., Results: The propositioned immunocontraceptive potentially remove and prevent the spread of BSF from endemic areas., Conclusions: We propose the anti-GnRH vaccine as a BSF prevention strategy based on these favorable results.

The bacterium Rickettsia rickettsii causes Brazilian spotted fever (BSF), a highly lethal disease that is transmitted by Amblyomma sculptum ticks in areas where capybaras ( Hydrochoerus hydrochaeris ) are the tick's major hosts. In this study, we evaluated the expansion of a capybara population in a residential park in São Paulo state, and the implications of such expansion to the occurrence of ticks and BSF. The capybara population was quantified during 2004-2013. In 2012, there was a BSF human case in the area, culminating in the complete fencing of the residential park and the official culling of all capybaras. Quantification of ticks in the environment was performed by dry ice traps from 2005 to 2018. Domestic dogs in 2006-2011 and capybaras in 2012 were serologically tested for the presence of anti- R. rickettsii antibodies. Our results show that capybara numbers increased ≈5 times from 2004 (41 capybaras) to 2012 (230 capybaras). Dry ice traps collected A. sculptum and Amblyomma dubitatum. The number of A. dubitatum adult ticks was generally higher than A. sculptum adults during 2005-2006; however, during 2012-2013, A. sculptum outnumbered A. dubitatum by a large difference. During 2016-2018 (after capybara culling), the number of both species fell close to zero. The low numbers of A. sculptum adult ticks during 2005-2006 coincided with relatively low capybara numbers (<80). Thereafter, in 2012, we counted the highest numbers of both A. sculptum ticks and capybaras (230 animals). All 40 canine blood samples were seronegative to R. rickettsii , in contrast to the 48.3% seropositivity (83/172) among capybaras. Our results support that the emergence of BSF in the residential park was a consequence of the increase of the local capybara population, which in turn, provided the increment of the A. sculptum population. Culling the entire capybara population eliminated the risks of new BSF cases.

Rickettsia spp. bacteria are responsible for tick-borne diseases worldwide, mostly maintained by rickettsial amplifiers capybaras in Brazilian endemic areas. The campus of the University of São Paulo, in southeastern Brazil, is an area endemic for Brazilian spotted fever (BSF), with high density of capybaras and Amblyomma spp., along with confirmed human cases. Besides capybaras, the university has also an in-campus high population of sheltered and free-roaming cats. Accordingly, the aim of this study was to determine the prevalence and characteristics associated with Rickettsia rickettsii, Rickettsia parkeri and Rickettsia felis exposure among cats in a BSF-endemic area. Out of 51 cats sampled, 23/35 shelter (65.7%) and 5/16 free-roaming (31.2%) were positive (titers ≥ 64) for at least one Rickettsia species. Ticks species were present in 3/16 free-roaming cats (18.8%), consisting of Amblyomma spp., nymphs of Amblyomma sculptum and adult Rhipicephalus sanguineus sensu lato. Despite sharing the capybaras environment, the seropositivity among the free-roaming and shelter cats was lower than owned cats in other endemic areas. Whether equally or less exposed to rickettsial infection, compared with owned cats in endemic areas, free-roaming and shelter cats may be used as environmental sentinels for human exposure to rickettsiae in such areas.

Ticks of the Amblyomma cajennense complex present high infestation rates. These ticks transmit the bacterium Rickettsia rickettsii, which causes Brazilian Spotted Fever. For this reason, an integrated tick control system was adopted on a farm in the municipality of Itu, state of São Paulo. On this farm, which borders the Tietê river, domestic animals are in contact with populations of capybaras. Six locations were monitored and evaluated between the years of 2015 and 2017. During this work 1271 nymphs and adult ticks were caught, all of them from the Amblyomma sculptum species, except for a single individual from the Amblyomma dubitatum species. The integrated tick management reduced the overall infestation levels to zero. Adult tick population dropped in the first year of the study, while larvae population dropped in the second year. Nymph population dropped in both years, decreasing in higher numbers in the first year. The estimated mean infestation levels for all of the tick's life cycle forms in the six monitored spots did not reach one individual in the end of the study. Estimated mean infestation levels for nymphs in these places equaled zero.

Rocky Mountain spotted fever (RMSF) has been reported in Colombia since 1937. Most recent outbreaks were in 2006-2008, followed by the absence of recognized cases. This report describes new clinical cases of RMSF and epidemiologic investigations. Medical records were reviewed, and fieldwork, serological and molecular diagnostic testing, and bacterial isolation were performed. Fever, hypotension, abdominal discomfort, and rash accompanied by thrombocytopenia and leukopenia were the most characteristic manifestations. Two convalescent sera from the index case and sera from two dogs revealed high anti-spotted fever group Rickettsia antibody titers. Rickettsia rickettsii was isolated from case 4. Cases 2 and 3 were identified by epidemiological connection with the index case. Thus, a new cluster of cases of RMSF was identified in Antioquia, Colombia, with the occurrence of fatal cases, which indicates the active circulation of the bacteria and a potential risk for the population.

There are a huge number of pathogens with multi-component transmission cycles, involving amplifier hosts, vectors or complex pathogen life cycles. These complex systems present challenges in terms of modeling and policy development. A lethal tick-borne infectious disease, the Brazilian Spotted Fever (BSF), is a relevant example of that. The current increase of human cases of BSF has been associated with the presence and expansion of the capybara Hydrochoerus hydrochaeris, amplifier host for the agent Rickettsia rickettsii and primary host for the tick vector Amblyomma sculptum. We introduce a stochastic dynamical model that captures the spatial distribution of capybaras and ticks to gain a better understanding of the spatial spread of the R. rickettsii and potentially predict future epidemic outcomes. We implemented a reaction-diffusion process in which individuals were divided into classes denoting their state with respect to the disease. The model considered bidirectional movements between base and destination locations limited by the carrying capacity of the environment. We performed systematic stochastic simulations and numerical analysis of the model and investigate the impact of potential interventions to mitigate the spatial spread of the disease. The mobility of capybaras and their attached ticks was significantly influenced by the birth rate of capybaras and therefore, disease propagation velocity was higher in places with higher carrying capacity. Some geographical barriers, generated for example by riparian reforesting, can impede the spatial spread of BSF. The results of this work will allow the formulation of public actions focused on the prevention of BSF human cases., Competing Interests: The authors have declared that no competing interests exist.

Brazilian Spotted Fever (BSF) is an emerging and lethal disease in South America which basic reproduction number (R 0 ) is unknown. Calculating R 0 for this disease is crucial to design control interventions and prevent human deaths. BSF endemic areas are related to the presence of capybaras Hydrochoerus hydrochaeris, amplifier hosts of Rickettsia rickettsii and primary hosts of the tick Amblyomma sculptum, main vector of the agent in this area. Because of the complexity of its dynamics, we calculated R 0 for the BSF system by constructing a next-generation matrix considering different categories of vectors and hosts. Each matrix element was considered as the expected number of infected individuals of one category produced by a single infected individual of a second category. We used field and experimental data to parameterize the next-generation matrix and obtain the final calculation (R 0  ≈ 1.7). We demonstrated the low impact of the matrix elements corresponding to the transovarial transmission and the transmission from infected larvae in the maintenance of R. rickettsii. Sensitivity and elasticity analyzes were performed to quantify the perturbations of each matrix element in R 0 . We noted that the elements equivalent to the number of infected attached nymphs produced by an infected capybara, and the number of infected capybaras produced by an infected attached nymph or adult are the major contributors to changes in R 0 . Our results provide insights into the strategic design of preventive interventions in BSF endemic areas., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

The Brazilian state of Goiás, untouched by spotted fever (SF) until 2012, has subsequently reported cases of the disease in several regions. This study aimed to survey the diversity of potential vectors and rickettsia in areas of Goiás under environmental surveillance or case investigation for SF. Collected specimens were assayed with molecular biology technology using DNA extraction, amplification and sequencing of fragments of the genes gltA, ompA, ompB and sca4 to detect rickettsia in ticks and fleas. Amplification of cytochrome oxidase subunit II and 16S rRNA was performed to assist tick identification. Rickettsia felis (Rickettsiales: Rickettsiaceae) was found in Ctenocephalides felis (Bouché, 1835) (Siphonaptera: Pulicidae). Rickettsia bellii was found in Amblyomma rotundatum Koch, 1844 (Ixodida: Ixodidae) and in Amblyomma cajennense sensu lato. Rickettsia sp. strain NOD was found in Amblyomma nodosum Neumann, 1899. Of the Amblyomma cajennense complex, Amblyomma sculptum Berlese, 1888 was confirmed in the northern, northeast, midwest and southeast regions of Goiás, whereas Amblyomma cajennense sensu stricto (Fabricius, 1787) was found only in the northern region of the state. Amblyomma dubitatum Neumann, 1899 associated with a species of the A. cajennense complex was the most common epidemiological finding, although Rickettsia rickettsii was not detected. This is the first report of Rickettsia sp. strain NOD in Goiás., (© 2018 The Royal Entomological Society.)

Rocky Mountain spotted fever (RMSF) is a severe tick-borne rickettsial illness. In the south-western United States and Mexico, RMSF displays unique epidemiologic and ecologic characteristics, including Rhipicephalus sanguineus sensu lato (brown dog tick) as the primary vector. Expansion and spread of the disease from hyperendemic regions of Arizona or Mexico to new areas is a key public health concern. Dogs are thought to play an important role in the emergence and circulation of R. rickettsii in these regions and are often one of earliest indicators of RMSF presence. A canine serosurvey was conducted in 2015 among owned and stray dogs at rabies clinic and animal shelters in three southern Arizona counties where RMSF had not previously been identified. Of the 217 dogs sampled, 11 (5.1%) tested positive for spotted fever group rickettsia (SFGR) IgG antibodies, with seropositivity ranging from 2.9% to 12.2% across the three counties. Large dogs were significantly more likely than small dogs to have positive titres reactive with R. rickettsii; no additional statistically significant relationships were observed between seropositivity of canine age, sex, neuter or ownership status. In addition, 17 (7.8%) dogs had ticks attached at the time of sampling, and stray dogs were significantly more likely to have ticks present than owned dogs (p < 0.001). All 57 ticks collected were identified as Rh. sanguineus s.l., and four (7%) had DNA evidence of genera-wide Rickettsia species. The results of this project demonstrated canine seroprevalence levels lower than those previously reported from dogs in highly endemic areas, indicating a low risk of SFGR transmission to humans in the southern Arizona border region at this time. Continued surveillance is critical to identify SFGR emergence in new geographic regions and to inform prevention efforts for humans and dogs in those areas., (© 2018 Blackwell Verlag GmbH.)

Amblyomma aureolatum ticks are vectors of Rickettsia rickettsii, the etiologic agent of Rocky Mountain spotted fever in Brazil. Maintenance of R. rickettsii in nature depends on horizontal transmission along tick generations. Although such transmission is known to occur when uninfected and infected ticks feed simultaneously on susceptible animals (co-feeding systemic transmission), we investigated co-feeding nonsystemic transmission, which was based on R. rickettsii-infected and -uninfected A. aureolatum ticks feeding simultaneously on guinea pigs immune to R. rickettsii. Our acquisition and transmission infestations demonstrated that horizontal transmission of R. rickettsii by co-feeding ticks on immune hosts with no systemic infection did not occur when uninfected larvae fed distantly from infected nymphs but did occur in a few cases when uninfected larvae fed side-by-side with infected nymphs, suggesting that they shared the same feeding site. The co-feeding nonsystemic transmission type might have no epidemiologic importance for Rocky Mountain spotted fever.

Since 2008, a large epidemic of Rocky Mountain spotted fever has been emerging among humans and dogs in Mexicali, adjacent to the United States in Baja California, Mexico. We molecularly confirmed the causative agent; this information can be used to study the origin and dynamics of the epidemic.

The distribution, abundance and seasonal activity of vector species, such as ticks and mosquitoes, are key determinants of vector-borne disease risk, and are strongly influenced by abiotic and habitat conditions. Despite the numerous species of tick vectors in the heavily populated North American West Coast, all but Ixodes pacificus, the primary vector of the Lyme disease spirochete, is poorly characterized with regard to seasonal activity patterns and fine scale drivers of distribution and abundance, particularly in heavily populated regions of southern California. This lack of knowledge inhibits both scientific understanding and public health efforts to minimize vector exposure and risk of pathogen transmission to humans. Here we address this gap by characterizing the abiotic and habitat drivers of the distribution, abundance, and diversity of the vector tick community using fine scale temporal surveys over two seasons (2014 and 2015) across coastal and inland regions of Santa Barbara County, CA. We also characterize patterns of seasonal activity of the more common vector species to understand seasonality in risk of vector exposure, and specifically focus on human encounter risk using standardized tick drags as our method of collection. Leveraging plot-level habitat and abiotic variables in partial least squares regression analysis, we find the seven different vector species collected in this study have divergent drivers of activity and abundance. For example, I. pacificus is strongly associated with dense forest habitats and cool and moist microclimates, while Dermacentor occidentalis and Dermacentor variabilis, competent vectors of Rocky Mountain Spotted Fever, were found to be more tolerant of higher average temperatures and more open habitats. These results suggest that I. pacificus may be expected to experience reductions in geographic distribution and seasonal activity under projected land cover and climate change in coastal southern California, while D. occidentalis may experience more limited effects. We discuss implications for changing tick-borne disease risk associated with pathogens transmitted by Ixodes as well as Dermacentor species ticks in the western US, and contrast these predictions with eastern North America., Competing Interests: The author has declared that no competing interests exist.

Increasing rates of Rocky Mountain spotted fever (RMSF) in the southwestern United States and northern Mexico underscore the importance of studying the ecology of the brown dog tick, Rhipicephalus sanguineus, the vector in that region. This species is reported to comprise distinct tropical and temperate lineages that may differ in vectorial capacity for RMSF and are hypothesized to be limited in their geographical range by climatic conditions. In this study, lineage was determined for ticks from 9 locations in California, Arizona, and Mexico by DNA sequencing of 12S, 16S, and D-loop ribosomal RNA. As expected, sites in northern California and eastern Arizona had temperate-lineage ticks, and phylogenetic analysis revealed considerable genetic variability among these temperate-lineage ticks. However, tropical-lineage ticks extended north from Oaxaca, Mexico were well established along the entire border from San Diego, California to western Arizona, and were found as far north as Lytle Creek near Los Angeles, California (a site where both lineages were detected). Far less genetic variability in the tropical lineage despite the large geographical distances is supportive of a hypothesis of rapid northward expansion. Discovery of the tropical lineage north of the identified climatic limitations suggests that more work is needed to characterize this tick's ecology, vectorial capacity, expansion, possible evolution, and response to climate change.

Dermacentor ticks are hard ticks found throughout most of North America and are easily identified by their large size, ornate scutum, and prominent dorsal pits. They are important disease vectors and are implicated in transmission of Rocky Mountain spotted fever (RMSF), Colorado tick fever, tularemia, and erlichiosis. They also are an important cause of fatal tick paralysis.

Ticks are obligate blood feeding ectoparasites that transmit a wide variety of pathogenic microorganisms to their vertebrate hosts. Amblyomma sculptum is vector of Rickettsia rickettsii , the causative agent of Rocky Mountain spotted fever (RMSF), the most lethal rickettsiosis that affects humans. It is known that the transmission of pathogens by ticks is mainly associated with the physiology of the feeding process. Pathogens that are acquired with the blood meal must first colonize the tick gut and later the salivary glands (SG) in order to be transmitted during a subsequent blood feeding via saliva. Tick saliva contains a complex mixture of bioactive molecules with anticlotting, antiplatelet aggregation, vasodilatory, anti-inflammatory, and immunomodulatory properties to counteract both the hemostasis and defense mechanisms of the host. Besides facilitating tick feeding, the properties of saliva may also benefits survival and establishment of pathogens in the host. In the current study, we compared the sialotranscriptome of unfed A. sculptum ticks and those fed for 72 h on rabbits using next generation RNA sequencing (RNA-seq). The total of reads obtained were assembled in 9,560 coding sequences (CDSs) distributed in different functional classes. CDSs encoding secreted proteins, including lipocalins, mucins, protease inhibitors, glycine-rich proteins, metalloproteases, 8.9 kDa superfamily members, and immunity-related proteins were mostly upregulated by blood feeding. Selected CDSs were analyzed by real-time quantitative polymerase chain reaction preceded by reverse transcription (RT-qPCR), corroborating the transcriptional profile obtained by RNA-seq. Finally, high-performance liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) analysis revealed 124 proteins in saliva of ticks fed for 96-120 h. The corresponding CDSs of 59 of these proteins were upregulated in SG of fed ticks. To the best of our knowledge, this is the first report on the proteome of A. sculptum saliva. The functional characterization of the identified proteins might reveal potential targets to develop vaccines for tick control and/or blocking of R. rickettsii transmission as well as pharmacological bioproducts with antihemostatic, anti-inflammatory and antibacterial activities.

Rocky Mountain spotted fever (RMSF) is an emerging public health concern near the US-Mexico border, where it has resulted in thousands of cases and hundreds of deaths in the past decade. We identified 4 patients who had acquired RMSF in northern Mexico and subsequently died at US healthcare facilities. Two patients sought care in Mexico before being admitted to US-based hospitals. All patients initially had several nonspecific signs and symptoms, including fever, headache, nausea, vomiting, or myalgia, but deteriorated rapidly without receipt of a tetracycline-class antimicrobial drug. Each patient experienced respiratory failure late in illness. Although transborder cases are not common, early recognition and prompt initiation of appropriate treatment are vital for averting severe illness and death. Clinicians on both sides of the US-Mexico border should consider a diagnosis of RMSF for patients with rapidly progressing febrile illness and recent exposure in northern Mexico.

Background: Amblyomma cajennense is the main vector of Rickettsia rickettsii which causes Brazilian spotted fever. This adult tick preferably infests horses and capybaras, but has low host specificity during its immature stages, thus posing a threat to humans and dogs. In this study, the efficacy of sarolaner (Simparic™/Simparica®, Zoetis) when administered once orally to dogs at 2 mg/kg was evaluated against induced infestations of A. cajennense nymphs for up to 35 days after treatment., Methods: Based on pretreatment tick counts, 20 dogs were randomly allocated to treatment with sarolaner (Simparic™) dosed at 2 mg/kg of body weight or a placebo on Day 0 of the study. Artificial infestations were performed using laboratory raised A. cajennense nymphs on study days -2, 5, 12, 19, 26 and 33. Efficacy was determined at 48 h post-treatment or post-infestation at each time point relative to the counts for dogs that received placebo., Results: There were no adverse reactions to treatment. A single dose of sarolaner (Simparic™) provided 100% efficacy on study days 2, 7 and 14; and ≥ 99.6% on days 21, 28 and 35. Geometric mean live tick counts for sarolaner were significantly lower than those for placebo on all days (P < 0.0001)., Conclusions: Under the conditions of the present study, sarolaner (Simparic™) administered once orally at 2 mg/kg provided 100% efficacy against existing infestations and ≥ 99.6% efficacy within 48 h against weekly challenges of A. cajennense for at least 35 days after treatment.

Background: Brazilian Spotted Fever (BSF), caused by the bacterium Rickettsia rickettsii, is the tick-borne disease that generates the largest number of human deaths in the world. In Brazil, the current increase of BSF human cases has been associated with the presence and expansion of capybaras Hydrochoerus hydrochaeris, which act as primary hosts for the tick Amblyomma sculptum, vector of the R. rickettsii in this area., Methods: We proposed a semi-discrete-time stochastic model to evaluate the role of capybaras in the transmission dynamics of R. rickettsii. Through a sensitivity analysis, we identified the parameters with significant influence on the R. rickettsii establishment. Afterward, we implemented the Gillespie's algorithm to simulate the impact of potential public health interventions to prevent BSF human cases., Results: The introduction of a single infected capybara with at least one infected attached tick is enough to trigger the disease in a non-endemic area. We found that to avoid the formation of new BSF-endemic areas, it is crucial to impede the emigration of capybaras from endemic areas by reducing their birth rate by more than 58%. Model results were corroborated by ex-situ data generated from field studies, and this supports our proposal to prevent BSF human cases by implementing control strategies focused on capybaras., Conclusion: The proposed stochastic model illustrates how strategies for the control and prevention of vector-borne infectious diseases can be focused on amplifier hosts management practices. This work provides a basis for future prevention strategies for other neglected vector-borne diseases.

Rickettsia rickettsii - the etiologic agent of Rocky Mountain spotted fever (RMSF) - is widely spread across the Americas. In the US, Dermacentor spp. ticks are identified as primary vectors of R. rickettsii and Rhipicephalus sanguineus s.l. has been implicated in transmission of this pathogen in several locations in the Southwest. Conversely, ticks of the genus Amblyomma are recognized vectors of RMSF in Central and South America, but not in the US. A. americanum is one of the most aggressive human-biting ticks in the US, whose geographical range overlaps with that of reported RMSF cases. Despite sporadic findings of R. rickettsii DNA in field-collected A. americanum and circumstantial association of this species with human RMSF cases, its vector competence for R. rickettsii has not been appropriately studied. Therefore, we assessed the ability of A. americanum to acquire and transmit two geographically distant isolates of R. rickettsii. The Di-6 isolate of R. rickettsii used in this study originated in Virginia and the AZ-3 isolate originated in Arizona. Under laboratory conditions, A. americanum demonstrated vector competence for both isolates, although the efficiency of acquisition and transovarial transmission was higher for Di-6 than for AZ-3 isolate. Uninfected larvae acquired the pathogen from systemically infected guinea pigs, as well as while feeding side by side with Rickettsia-infected ticks on non-rickettsiemic hosts. Once acquired, R. rickettsii was successfully maintained through the tick molting process and transmitted to susceptible animals during subsequent feedings. Guinea pigs and dogs infested with infected A. americanum developed fever, scrotal edema and dermatitis or macular rash. R. rickettsii DNA was identified in animal blood, skin, and internal organs. The prevalence of infection within tick cohorts gradually increased due to side-by-side feeding of infected and uninfected individuals from 33 to 49% in freshly molted nymphs to 71-98% in engorged females. Moreover, R. rickettsii was transmitted transovarially by approximately 28% and 14% of females infected with Di-6 and AZ-3 isolates, respectively. Hence, A. americanum is capable of acquiring, maintaining and transmitting R. rickettsii isolates originating from two different geographical regions of the US, at least under laboratory conditions. Its role in ecology and epidemiology of RMSF in the US deserves further investigation., (Published by Elsevier GmbH.)

Rickettsia rickettsii is a tick-borne obligate intracellular bacterium that causes Rocky Mountain Spotted Fever (RMSF). In Brazil, two species of ticks in the genus Amblyomma, A. sculptum and A. aureolatum , are incriminated as vectors of this bacterium. Importantly, these two species present remarkable differences in susceptibility to R. rickettsii infection, where A. aureolatum is more susceptible than A. sculptum . In the current study, A. aureolatum and A. sculptum ticks were fed on suitable hosts previously inoculated with R. rickettsii , mimicking a natural infection. As control, ticks were fed on non-infected animals. Both midgut and salivary glands of all positively infected ticks were colonized by R. rickettsii . We did not observe ticks with infection restricted to midgut, suggesting that important factors for controlling rickettsial colonization were produced in this organ. In order to identify such factors, the total RNA extracted from the midgut (MG) was submitted to next generation RNA sequencing (RNA-seq). The majority of the coding sequences (CDSs) of A. sculptum differentially expressed by infection were upregulated, whereas most of modulated CDSs of A. aureolatum were downregulated. The functional categories that comprise upregulated CDSs of A. sculptum , for instance, metabolism, signal transduction, protein modification, extracellular matrix, and immunity also include CDSs of A. aureolatum that were downregulated by infection. This is the first study that reports the effects of an experimental infection with the highly virulent R. rickettsii on the gene expression of two natural tick vectors. The distinct transcriptional profiles of MG of A. sculptum and A. aureolatum upon infection stimulus strongly suggest that molecular factors in this organ are responsible for delineating the susceptibility to R. rickettsii . Functional studies to determine the role played by proteins encoded by differentially expressed CDSs in the acquisition of R. rickettsii are warranted and may be considered as targets for the development of strategies to control the tick-borne pathogens as well as to control the tick vectors.

The aim of this work was to test the vectorial competence of Amblyomma tonelliae (Ixodida: Ixodidae) to transmit Rickettsia rickettsii (Rickettsiales: Rickettsiaceae), the agent of Rocky Mountain spotted fever (RMSF). All parasitic stages of A. tonelliae were exposed to R. rickettsii by allowing each stage to feed on hosts inoculated with this pathogen. Thereafter, ticks were fed on uninfected hosts. All stages of A. tonelliae were able to acquire the R. rickettsii infection and maintain it by transstadial and transovarial transmission. When infected ticks fed on uninfected hosts, the hosts developed rickettsiosis disease. This study demonstrates the vectorial competence of A. tonelliae to transmit R. rickettsii. These results have epidemiological relevance because A. tonelliae is one of the tick species most likely to infest humans in Argentina, including in areas in which RMSF has been reported., (© 2016 The Royal Entomological Society.)

The zoonotic transmission cycles of Rickettsia rickettsii and other spotted fever group (SFG) rickettsiae in Latin America have usually been associated with rural or sylvatic environments, although domestic dogs can be implicated in more populated settings. In this study, exposure of dogs to SFG rickettsiae in the Greater Metropolitan Area of Costa Rica was investigated. Dogs from sites associated with human cases and from dog shelters were evaluated by indirect immunofluorescence assay (IFA) using antigen of SFG rickettsiae. Rickettsia spp. were detected in ectoparasites by polymerase chain reaction (PCR). A total 18.5% (31/168) of dogs associated with human cases and 6.8% (11/161) of dogs in shelters had IgG end titers≥64 to Rickettsia spp. The odds of being seropositive were greater in dogs from areas associated with human cases when compared to shelters (OR: 3.2; 95% C.I: 1.5-5.6). Rhipicephalus sanguineus sensu lato (s. l.) was present in all sites associated with human cases. Rickettsia felis URRWXCal2 and R. felis-like RF2125 were detected in Ctenocephalides felis, and Rickettsia sp. IbR/CRC in Ixodes boliviensis. Results demonstrate that dogs from the main urban center of Costa Rica have been exposed to SFG rickettsiae, especially in areas with known human infection. Both human and animal health sectors must be aware of possible rickettsial diseases in urban areas, where dogs may also serve as sentinels for human infection., (Copyright © 2016 Elsevier GmbH. All rights reserved.)

Rocky Mountain spotted fever, caused by Rickettsia rickettsii, is a potentially fatal tick-borne disease spread from North America to Argentina. The major vectors of R. rickettsii in the United States are Dermacentor andersoni Stiles and Dermacentor variabilis (Say). It is generally believed that vector ticks serve as major reservoirs of R. rickettsii in nature; however, the ability of ticks to support the indefinite perpetuation of R. rickettsii has been challenged by reports of deleterious effects of rickettsial infection on D. andersoni. To better elucidate the relationship of the pathogen with D. variabilis, we assessed the effects of R. rickettsii on the survival, fertility, and fecundity of D. variabilis. We used an isolate of R. rickettsii (Di-6), originally acquired from an opossum caught in Virginia, and ticks from a laboratory colony established from adult D. variabilis also collected in Virginia. Overall, infection with R. rickettsii protracted the feeding periods of all life stages of ticks. Infected nymphal and adult ticks experienced a slight decrease in feeding success compared with the uninfected colony, but neither larval nor nymphal molting success was affected. Infected females reached smaller engorgement weights, were less efficient in conversion of bloodmeal into eggs, and produced smaller egg clutches with a lower proportion of eggs hatching. However, no sudden die-off was observed among infected ticks, and longevity was not decreased due to R. rickettsii infection in any stage. Although infection with the studied isolate of R. rickettsii caused slight decrease in fecundity in sympatric vector ticks, no obvious deleterious effects were observed., (Published by Oxford University Press on behalf of Entomological Society of America 2015. This work is written by US Government employees and is in the public domain in the US.)

Introduction: Brazilian spotted fever (BSF) is a disease transmitted by ticks for which the etiological agent is Rickettsia rickettsii. The present essay evaluates the risk factors associated with the transmission of cases of BSF in the time period between 2003 and 2013 in the Piracicaba river basin, state of São Paulo., Methods: This essay presents a retrospective study to identify the factors associated with the transmission of cases of BSF among all suspected cases identified by the System for Epidemiological Surveillance of São Paulo (CVE). After the description of temporal distribution (onset of symptoms) and the environmental and demographic variations of the confirmed and discarded cases, a multiple logistic regression model was applied., Results: We searched 569 probable locations of infection (PLI) with 210 (37%) confirmed cases of BSF and 359 (63%) discarded cases. The associated variables for the confirmation of BSF in the multiple logistic model using a confidence interval (CI) of 95% were age (OR = 1.025 CI: 1.015-1.035), the presence of Amblyomma sculptum in the environment (OR = 1.629 CI: 1.097-2.439), the collection of ticks from horses (OR = 1.939 CI: 0.999-3.764), the presence of capybaras (OR = 1.467 CI: 1.009-2.138), an urban environment (OR = 1.515 CI: 1.036-2.231), and the existence of a dirty pasture (OR = 1.759 CI: 1.028-3.003)., Conclusions: The factors associated with the confirmation of BSF cases included an urban environment, age, presence of the A. sculptum vector, the collection of ticks from horses, the presence of a capybara population, and a dirty pasture environment.

Rocky Mountain spotted fever (RMSF) transmitted by the brown dog tick (Rhipicephalus sanguineus sensu lato) has emerged as a significant public health risk on American Indian reservations in eastern Arizona. During 2003-2012, more than 250 RMSF cases and 19 deaths were documented among Arizona's American Indian population. The high case fatality rate makes community-level interventions aimed at rapid and sustained reduction of ticks urgent. Beginning in 2012, a two year pilot integrated tick prevention campaign called the RMSF Rodeo was launched in a ∼ 600-home tribal community with high rates of RMSF. During year one, long-acting tick collars were placed on all dogs in the community, environmental acaricides were applied to yards monthly, and animal care practices such as spay and neuter and proper tethering procedures were encouraged. Tick levels, indicated by visible inspection of dogs, tick traps and homeowner reports were used to monitor tick presence and evaluate the efficacy of interventions throughout the project. By the end of year one, <1% of dogs in the RMSF Rodeo community had visible tick infestations five months after the project was started, compared to 64% of dogs in Non-Rodeo communities, and environmental tick levels were reduced below detectable levels. The second year of the project focused on use of the long-acting collar alone and achieved sustained tick control with fewer than 3% of dogs in the RMSF Rodeo community with visible tick infestations by the end of the second year. Homeowner reports of tick activity in the domestic and peridomestic setting showed similar decreases in tick activity compared to the non-project communities. Expansion of this successful project to other areas with Rhipicephalus-transmitted RMSF has the potential to reduce brown dog tick infestations and save human lives.

Amblyomma dubitatum engorged females, naturally infected by Rickettsia bellii, were used to establish a laboratory colony. Larvae, nymphs, and adults were exposed to two strains of Rickettsia rickettsii by feeding on needle-inoculated guinea pigs, and thereafter reared on uninfected guinea pigs. After acquisition feeding, engorged larvae and nymphs molted to nymphs and adults, respectively, which were shown to be infected (confirming transstadial perpetuation), and were able to transmit both strains of R. rickettsii to uninfected animals, as demonstrated by clinical, serological, and molecular analyses. However, the larval, nymphal, and adult stages of A. dubitatum showed to be only partially susceptible to R. rickettsii infection, since in all cases, only part of the ticks became infected by this agent, after being exposed to rickettsemic animals. While transovarial transmission of R. rickettsii was inefficient in the A. dubitatum engorged females of the present study, 100% of these females passed R. bellii transovarially. Because it has been reported that a primary infection by a Rickettsia species would preclude transovarial transmission of a second Rickettsia species, it is likely that the ineffectiveness of A. dubitatum to perpetuate R. rickettsii by transovarial transmission was related to its primary infection by R. bellii; however, it could also be related to unknown factors inherent to A. dubitatum. The relevance of A. dubitatum as a natural vector of R. rickettsii to humans or animals is discussed., (Copyright © 2014 Elsevier GmbH. All rights reserved.)

Rocky Mountain spotted fever is endemic to the São Paulo metropolitan area, Brazil, where the etiologic agent, Rickettsia rickettsii, is transmitted to humans by adult Amblyomma aureolatum ticks. We determined the minimal feeding period required by A. aureolatum nymphs and adults to transmit R. rickettsii to guinea pigs. Unfed nymphs and unfed adult ticks had to be attached to the host for >10 hours to transmit R. rickettsii. In contrast, fed ticks needed a minimum of 10 minutes of attachment to transmit R. rickettsii to hosts. Most confirmed infections of Rocky Mountain spotted fever in humans in the São Paulo metropolitan area have been associated with contact with domestic dogs, the main host of A. aureolatum adult ticks. The typical expectation that transmission of tickborne bacteria to humans as well as to dogs requires ≥2 hours of tick attachment may discourage persons from immediately removing them and result in transmission of this lethal bacterium.

Background: Brazilian spotted fever (BSF), caused by the bacterium Rickettsia rickettsii, is the deadliest spotted fever of the world. In most of the BSF-endemic areas, capybaras (Hydrochoerus hydrochaeris) are the principal host for the tick Amblyomma cajennense, which is the main vector of BSF., Methods: In 2012, a BSF case was confirmed in a child that was bitten by ticks in a residential park area inhabited by A. cajennense-infested capybaras in Itú municipality, southeastern Brazil. Host questing A. cajennense adult ticks were collected in the residential park and brought alive to the laboratory, where they were macerated and intraperitoneally inoculated into guinea pigs. A tick-inoculated guinea pig that presented high fever was euthanized and its internal organs were macerated and inoculated into additional guinea pigs (guinea pig passage). Tissue samples from guinea pig passages were also used to inoculate Vero cells through the shell vial technique. Infected cells were used for molecular characterization of the rickettsial isolate through PCR and DNA sequencing of fragments of three rickettsial genes (gltA, ompA, and ompB). Blood serum samples were collected from 172 capybaras that inhabited the residential park. Sera were tested through the immunofluorescence assay using R. rickettsii antigen., Results: A tick-inoculated guinea pig presented high fever accompanied by scrotal reactions (edema and marked redness). These signs were reproduced by consecutive guinea pig passages. Rickettsia was successfully isolated in Vero cells that were inoculated with brain homogenate derived from a 3rd passage-febrile guinea pig. Molecular characterization of this rickettsial isolate (designated as strain ITU) yielded DNA sequences that were all 100% identical to corresponding sequences of R. rickettsii in Genbank. A total of 83 (48.3%) out of 172 capybaras were seroreactive to R. rickettsii, with endpoint titers ranging from 64 to 8192., Conclusions: A viable isolate of R. rickettsii was obtained from the tick A. cajennense, comprising the first viable R. rickettsi isolate from this tick species during the last 60 years. Nearly half of the capybara population of the residential park was seroreactive to R. rickettsii, corroborating the findings that the local A. cajennense population was infected by R. rickettsii.

Spotted-fever-caused Rickettsia rickettsii infection is in Brazil the major tick-borne zoonotic disease. Recently, a second and milder human rickettsiosis caused by an agent genetically related to R. parkeri was discovered in the country (Atlantic rainforest strain). Both diseases clearly have an ecological background linked to a few tick species and their environment. Capybaras (Hydrochoerus hydrochaeris) and Amblyomma cajennense ticks in urban and rural areas close to water sources are the main and long-known epidemiological feature behind R. rickettsii-caused spotted-fever. Unfortunately, this ecological background seems to be increasing in the country and disease spreading may be foreseen. Metropolitan area of São Paulo, the most populous of the country, is embedded in Atlantic rainforest that harbors another important R. rickettsii vector, the tick Amblyomma aureolatum. Thus, at the city-forest interface, dogs carry infected ticks to human dwellings and human infection occurs. A role for R. rickettsii vectoring to humans of a third tick species, Rhipicephalus sanguineus in Brazil, has not been proven; however, there is circumstantial evidence for that. A R. parkeri-like strain was found in A. ovale ticks from Atlantic rainforest and was shown to be responsible for a milder febrile human disease. Rickettsia-infected A. ovale ticks are known to be spread over large areas along the Atlantic coast of the country, and diagnosis of human infection is increasing with awareness and proper diagnostic tools. In this review, ecological features of the tick species mentioned, and that are important for Rickettsia transmission to humans, are updated and discussed. Specific knowledge gaps in the epidemiology of such diseases are highlighted to guide forthcoming research.