Larval behavioral diapause regulates life cycle of Amblyomma cajennense (Acari: Ixodidae) in Southeast Brazil

A long-term study on free-ranging jaguar-tick interactions, featuring a novel report of Amblyomma incisum adult infestation

Over nearly 12 years, we collected ticks from free-ranging jaguars (Panthera onca) and performed statistical analyses to comprehend the vector-host relationship throughout the seasons. We evaluated the presence and number of ticks, as well as their association with weight, age, and gender of captured jaguars in the Pantanal and Amazon biomes. Out of 100 captured jaguars (comprising 72 initial captures and 28 recaptures, with 41 females and 31 males), 77 were found to be infested by different tick species. We gathered a total of 1,002 ticks, categorized by the following species in descending order of abundance: Amblyomma sculptum, Amblyomma ovale, Rhipicephalus microplus, Amblyomma triste, Amblyomma cajennense sensu stricto, Amblyomma incisum, and Amblyomma spp. larvae. Apart from weight, statistical analysis indicated that age, gender and seasonality does not significantly affect the presence of different tick species in free ranging jaguars. Notably, A. sculptum adults were more abundant in the first semester, while A. sculptum nymphs and Amblyomma spp. larvae were mainly found during dry months, aligning with their expected life cycle stages. This is the first long-term study in jaguars to correlate seasonality and host factors and also the first time an adult of A. incisum is reported infesting a jaguar.

Density and behavior of capybara (Hydrochoerus hydrochaeris) ticks (Acari: Ixodidae) Amblyomma sculptum and Amblyomma dubitatum with notes on Rickettsia bellii infection: Assessing human exposure risk

In several urban and peri‑urban areas of Brazil, populations of Amblyomma sculptum and Amblyomma dubitatum ticks are maintained by capybaras (Hydrochoerus hydrochaeris). In some of these areas, this host and these tick species are associated with Brazilian spotted fever (BSF), a lethal human disease caused by the bacterium Rickettsia rickettsii. In this work, we evaluated the risk of human exposure to these tick species using four collection techniques to discern host-seeking behavior. The study was carried out in 10 urban sites inhabited by capybaras in Uberlândia, a BSF-free municipality in southeastern Brazil. Ticks were collected in areas of 400 m2 at each site and at three seasons. Within the same municipality, the distance and speed of A. sculptum nymphs moving towards the CO2 traps were evaluated. In a sample of ticks Rickettsia DNA was investigated. During the study period, 52,953 ticks were collected. Among these, 83.4 % were A. sculptum (1,523 adults, 10,545 nymphs and 32,104 larvae) and 16.6 % were A. dubitatum (464 adults, 2,153 nymphs and 6,164 larvae). An average annual questing tick density of 4.4/m² was observed, with the highest density recorded at one site in autumn (31.8/m²) and the lowest in summer at another site (0.03/m²). The visual search yielded the highest proportion of A. sculptum larvae, constituting 47 % of the total and 63.6 % of all A. sculptum larvae. In contrast, CO2 traps collected a greater proportion of nymphs and adults of A. sculptum ticks. In the case of A. dubitatum, the CO2 trap was the most efficient technique with 57.7 % of captures of this species, especially of nymphs (94.5 % of captures) and adults (97.8 % of captures). Ticks' ambush height on vegetation (9 to 77 cm), observed by visual search 30 times, yielded a total of 20,771 ticks. Of these, 28 (93 %) were A. sculptum ticks, with only two (7 %) identified as A. dubitatum ticks. Among A. sculptum ticks, the nymph was the most attracted stage to humans and larva in the case of A. dubitatum. Amblyomma sculptum adults and nymphs were significantly more attracted to humans than those of A. dubitatum, but A. dubitatum larvae were significantly more attracted than the same stage of A. sculptum. The maximum distance and speed of horizontal displacement for A. sculptum nymphs were five meters and 2.0 m/h, respectively. The only species of Rickettsia detected in ticks, exclusively in A. dubitatum, was R. bellii. Importantly, it was observed that the higher the proportion of A. sculptum in the community of ticks, the lower the rate of infection of A. dubitatum by R. bellii. In conclusion, host-seeking behavior differed between the two tick species, as well as between stages of the same species. A greater restriction of A. dubitatum ticks to the soil was observed, while larvae and nymphs of A. sculptum dispersed higher in the vegetation. The behavior presented by A. sculptum provides greater opportunities for contact with the hosts, while A. dubitatum depends more on an active search for a host, the hunter behavior. Taken together, these observations show that a human being crossing an area infested with A. sculptum and A. dubitatum ticks will have almost exclusive contact with A. sculptum larvae and/or nymphs. Humans in a stationary position (sitting, lying or immobile) are exposed to both tick species, but they are more attractive to adults and mainly nymphs of A. sculptum compared to the corresponding stages of the tick A. dubitatum. The negative effect of A. sculptum on A. dubitatum infection by R. bellii deserves further studies.

Biology of the non-parasitic phase of the cattle tick Rhipicephalus (Boophilus) microplus in an area of Amazon influence

BACKGROUND

Rhipicephalus (Boophilus) microplus is the most important tick species affecting cattle in the world. Under field conditions, the non-parasitic phase of R. (B.) microplus is unknown in the Amazon biome, including Brazil. The present study aimed to evaluate the non-parasitic phase of R. (B.) microplus in field (grass plots) and laboratory conditions.

METHODS

The study was conducted from September 2020 to April 2022 in an Amazonian region (Maranhão State, Brazil). We evaluated the biological parameters of R. (B.) microplus under laboratory and field conditions. Engorged females were exposed to experimental conditions every 14 days, totaling 20 months of study. The following biological parameters were observed: pre-oviposition period, egg mass incubation period, and maximum larval survival period.

RESULTS

Abiotic data (e.g., temperature and humidity) varied little throughout the year. Precipitation was the factor that varied the most throughout the year (dry ~ 30 mm3 and rain 400 mm3), and the parameters of pre-oviposition and pre-hatching are longer during the rainy season. A possible negative effect of the dry season on the percentage of hatched eggs was observed. Larval longevity in the plots of both control and free females was short (mean ~ 50-60 days), below that recorded for larvae under controlled conditions (mean ~ 95 days).

CONCLUSIONS

Rhipicephalus (Boophilus) microplus was able to complete its non-parasitic phase by producing host-seeking larvae in the pasture during all months of the study. The results indicate that R. (B.) microplus can complete up to six generations per year in biome Amazon. To our knowledge, this is the highest number of annual generations for R. (B.) microplus in Latin America.

Seasonal dynamics of Amblyomma cajennense (Fabricius, 1787) sensu stricto in a degraded area of the Amazon biome, with notes on Rickettsia amblyommatis infection

BACKGROUND

The tick Amblyomma cajennense sensu stricto (A. cajennense s.s.) frequently parasitizes animals and humans in the Amazon biome, in addition to being a vector of Rickettsia amblyommatis. In the present study, we evaluated both the population dynamics of A. cajennense s.s. in a degraded area of the Amazon biome and the presence of rickettsial organisms in this tick population.

METHODS

The study was carried out in a rural area of the Santa Inês municipality (altitude: 24 m a.s.l.), Maranhão state, Brazil. Ticks were collected from the environment for 24 consecutive months, from June 2021 to May 2023. The region is characterized by two warm seasons: a rainy season (November-May) and a dry season (June-October). We characterized the temporal activity of A. cajennense s.s. on the vegetation by examining questing activity for each life stage (larvae, nymphs, adults [males and females]) in relation to the dry and rainy season. Ticks collected in this study were randomly selected and individually tested by a TaqMan real-time PCR assay that targeted a 147-bp fragment of the rickettsial gltA gene.

RESULTS

Overall, 1843 (62.4%) adults (52.6% females, 47.4% males), 1110 (37.6%) nymphs and 398 larval clusters were collected. All adult females and nymphs were morphologically identified as A. cajennense s.s. Larval activity was observed from April to December, with a peak from June to September (dry season); nymph abundance peaked from September to November (transition period between dry and rainy seasons); and adult ticks were abundant from October to May (spring/summer/early autumn). The infection rate by R. amblyommatis in A. cajennense s.s. ticks was at least 7% (7/99).

CONCLUSION

Our data suggest a 1-year generation pattern for A. cajennense s.s., with a well-defined seasonality of larvae, nymphs and adults in the Amazon biome. Larvae predominate during the dry season, nymphs are most abundant in the dry-rainy season transition and adults are most abundant in the rainy season. The presence of R. amblyommatis in adult ticks suggests that animals and humans in the study region are at risk of infection by this species belonging to the spotted fever group of Rickettsia.

Soft and hard ticks (Parasitiformes: Ixodida) on humans: A review of Brazilian biomes and the impact of environmental change

Records of accidental parasitism by ticks in humans from Brazil are scarce, with most being reported by researchers who are parasitized during their research and by professionals who work with animals. In order to compile these records, an extensive literature review was carried out. Our revision includes studies published between 1909 and 2022, including nine species of the Argasidae family and 32 species of the Ixodidae family that were reported biting humans in the six biomes of the Brazilian territory. The species with the highest number of records of human parasitism was Amblyomma sculptum, followed by Amblyomma coelebs, Amblyomma cajennense sensu stricto, and Amblyomma brasiliense. The Atlantic Forest was the most frequent biome where human parasitism occurred, probably due to the greater number of inhabitants, universities, and researchers in the region; however, this does not mean that this biome is more conducive to the development of ticks and their parasitism in humans. In addition to Amblyomma ovale, a vector of Rickettsia parkeri in the country, two of the main species that act as vectors of Rickettsia rickettsii, A. sculptum, and Amblyomma aureolatum, have been reported, which is quite worrying considering that the wide distribution of the species and life stages most frequently mentioned in parasitism (i.e., nymphs and adults) are the ones that favour pathogen transmission. This research provides a significant contribution to the knowledge of tick species associated with human parasitism in Brazil; however, due to environmental change potentiated by deforestation and fires, it is expected that there will be a geographic expansion of some tick species and the pathogens that use them as a vector and an increase in human parasitism.

Seasonal dynamics of Amblyomma sculptum: a review

BACKGROUND

Amblyomma sculptum is a hard tick that is associated with domestic animals and the transmission of Brazilian spotted fever. This association has motivated several field studies on this ixodid tick within its distribution area in South America. Thorough knowledge of the seasonal dynamics of A. sculptum in different ecological scenarios is required in order to better understand the biological characteristics of this tick and develop techniques for the control and prevention of diseases transmitted by this vector. In this article, we systematically review the seasonal dynamics of A. sculptum and tick collection methodology.

METHODS

A systematic search of the Scopus, Web of Science, PubMed and Scielo databases was carried out for articles (including dissertations and theses) on the population dynamics of A. sculptum. The inclusion criterion was the report of seasonal dynamic studies on A. sculptum through surveys carried out for at least 1 year with, as methodology, tick collection in the environment and/or tick count/collection on A. sculptum primary hosts (horses or capybaras). Studies carried out before the reclassification of Amblyomma cajennense sensu lato in 2014, which referred to Amblyomma cajennense in areas where it is currently known that only A. sculptum occurs, were also included. Articles meeting the inclusion criterion, but not available in online databases, were also added based on the authors' experience on the subject. Sixteen articles and one thesis were selected for inclusion in this systematic review.

RESULTS

Most of the studies were carried out in the southeastern region of Brazil, with a few also carried out in the northeast, center-west and south of Brazil and northwest of Argentina. Five techniques/methods were applied across these studies: CO₂ traps, dragging, flagging, visual searches and tick counting on animals, used alone or in combination.

CONCLUSION

Seasonal dynamics of A. sculptum was found to be similar in almost all of the areas studied, with larvae predominating during the autumn, nymphs in the winter and adults in the spring and summer.

Rhipicephalus microplus and Amblyomma sculptum (Ixodidae) infestation of Nellore cattle (Bos taurus indicus) in a farm of the Brazilian Cerrado: seasonality and infestation patterns

We herein describe zebuine cattle tick infestation in a farm in southeast Brazil with an examination accurate enough to detect tick immatures and species other than R. microplus. Cattle were inspected monthly for ticks from May 2015 to May 2017 and 7604 ticks were collected along 276 bovine inspections. Rhipicephalus microplus was the dominant species (7197 specimens, 94.5% from the total), but Amblyomma sculptum was also collected (407/5.5%). Horse tick infestations were evaluated for comparison purposes of A. sculptum infestations of a primary host sharing pastures with bovines. Ticks were counted on the left side of 4-12 horses every 3 months from October 2015 to October 2017. Overall, 68 horse inspections were performed and 1702 ticks were collected: Dermacentor nitens (805 specimens/47.3% of the total), A. sculptum (733/43.1%) and R. microplus (164/9.6%). Overall mean tick abundance on bovines was low if compared to that of taurine cattle and counting revealed four annual generations of R. microplus. The interval between infestation peaks was 3 months, irrespective of the season, and an increase in tick counts from spring onward, as described in the south of Brazil, was not seen. Amblyomma sculptum infestation abundance was minor but constant and in high prevalence. Cattle infestation with A. sculptum seems to depend on pasture sharing with other domestic and wild hosts that are its primary hosts and provide engorged females to complete their life cycle. The impact of such tick sharing among several host species on tick-borne pathogen transmission remains to be elucidated.

Parasitism by Amblyomma humerale (Acari: Ixodidae) on Chelonoidis denticulatus (Testudines: Testudinidae) in the Atlantic Forest

The present study reports on patterns of parasitism by Amblyomma humerale on yellow-footed tortoise, Chelonoidis denticulatus, in the Atlantic Forest of southeastern Brazil. The tortoises were sampled occasionally, from July 2005 to January 2020. We collected 81 adult ticks from seven tortoises (mean = 11.57 ± 6.90 ticks/host), of which 72 were males (88.9%) and nine females (11.1%), resulting in an 8:1 sex ratio (males:females). Males were found in clusters, attached to the carapace. Females occurred mainly isolated, attached to coriaceous integumental areas (n = 7; 77.8%), especially the engorged females (100%). We suggest that the difference between attachment sites is a strategy used by fertilized females to avoid mechanical removal from their host through friction with elements of the environment. Because they undergo a considerable increase of volume when engorged, they move to more sheltered places on their host's surface. The parasitism patterns by A. humerale on C. denticulatus were compatible with those observed in the Amazon region and in the Cerrado-Amazonia transition. The present work provides information about the life history and host-parasite interface of the two species and contributes to understanding the parasitism patterns by A. humerale on C. denticulatus in the Atlantic Forest of southeastern Brazil.

Seasonal dynamics of Amblyomma sculptum in two areas of the Cerrado biome midwestern Brazil, where human cases of rickettsiosis have been reported

Amblyomma sculptum is a common human-biting tick in Brazil, where it plays an important role as a vector of Rickettsia rickettsii, the agent of the Brazilian spotted fever. Herein, we studied the seasonal dynamics of A. sculptum in an urban area of the Cerrado biome in midwestern Brazil, where human rickettsiosis is endemic. Ticks were collected in two sites located within the campus of Federal University of Goiás. The collections were done by dragging, flagging and visual search. In total, 117,685 ticks were collected, including 100,627 Amblyomma spp. larvae, 10,055 nymphs and 6977 adults of A. sculptum, and one nymph and 25 adults of Amblyomma dubitatum. The highest peak of larvae occurred in June 2018 and in July 2019, whereas nymphs peaked in July 2018 and September 2019. Adults reached their highest numbers in March 2018 and November 2019. These data suggest that A. sculptum develops one generation per year in this urban area of the Cerrado biome in midwestern Brazil. Interestingly, the peak of nymphs occurred during the same period of all confirmed cases of rickettsiosis in Goiás, suggesting a possible relationship between the seasonal dynamics of this tick stage and rickettsiosis transmission in this state.

The nonparasitic phase of Dermacentor nitens under field conditions in southeastern Brazil

Dermacentor nitens is a one-host tick that uses domestic equids as main hosts. Herein, the nonparasitic phase of D. nitens was evaluated under field conditions in Pirassununga, São Paulo state, Southeastern Brazil. By exposing engorged females of D. nitens to field conditions (grass plots) for 24 consecutive months, this tick species was able to complete its nonparasitic phase by producing host-seeking larvae in the pasture throughout the year. Preoviposition and egg incubation periods were longer during autumn and winter months than during the other months. The number of larvae generated by engorged females was in most of the times lower during autumn and winter months, as demonstrated by lower egg hatching values. Such conditions could be linked to lower mean temperatures and rainfall. Larvae with the longest longevity hatched from the eggs with the shortest incubation periods. An apparent synchronism of larval hatching during spring was observed from the eggs laid by females during late winter and autumn, which is consistent with the phenomenon of "spring rise". The results indicate that D. nitens can complete up to five generations per year in southeastern Brazil, providing baseline data to develop future protocols for the appropriate control of D. nitens on horses.

Locomotion activity and its effects on the survival of Amblyomma sculptum (Acari: Ixodidae) nymphs under laboratory conditions

The active locomotion of ticks is directly associated with the epidemiology of tick-borne diseases, as it has important implications for the interaction of ticks with their hosts and their dispersion in the environment. In an attempt to elucidate the factors involved in the dispersion of Amblyomma sculptum, the present work aimed to characterize different aspects of the active locomotion of A. sculptum nymphs under laboratory conditions. To this end, nymphs were placed on a string at a 70° inclination and their walking activity was recorded daily along with their survival period. During their lifetime, ticks walked an average of 110 m. Their locomotion was not in a straight line and nymphs changed direction 142 times throughout their lifetimes. The mean distance walked per experimental day was 1.8 m, while the average walking distance before changing direction was 52 cm. The distance walked per experimental day reduced over time. The survival of ticks was affected by walking; resting nymphs survived for over 6 months, while the survival of those that walked daily was reduced to approximately 62 days. The results showed that A. sculptum nymphs were able to cover distances of over 100 m throughout their lifetimes, but they walked short distances at a time and constantly changed direction. This behavior indicates that ticks are not able to disperse over long distances by means of active locomotion.

Ticks biting humans in the Brazilian savannah: Attachment sites and exposure risk in relation to species, life stage and season

Information about human tick bites in Brazil is mostly anecdotal. Published information is typically restricted to single tick infestation episodes and does not address human exposure occurring on a daily basis in natural, rural, or green urban areas. We present a comprehensive 2-yr study on human parasitism during a broad survey on ticks within a Brazilian savannah reserve. Overall, 439 tick bites were recorded from the following species: Amblyomma sculptum (n = 331 bites), Amblyomma parvum (n = 64), Amblyomma auricularium (n = 3), Rhipicephalus microplus (n = 2), Dermacentor nitens (n = 1) and 38 Amblyomma spp. ticks. Nymphs accounted for most tick bites (n = 292, 66.5 % of all bites) and these were overwhelmingly A. sculptum (92.8 % of nymphal bites). The main adult tick biting humans was A. parvum (n = 61, 50 % of all adult tick bites) followed closely by A. sculptum (n = 58, 47.5 % of all adult tick bites). Winter was the season with the highest percentage of tick bites (39.7 % of all bites), followed by spring (32.4 %); summer (18.9 %) and autumn (9 %). Amblyomma sculptum adult bites peaked in summer whereas nymphal bites occurred primarily in winter and spring. Amblyomma parvum adult bites peaked in spring and summer. The most common tick attachment sites included the waist, legs and belly, but A. parvum adults were recorded from the head of humans as well. A noteworthy observation was the lack of human parasitism by Amblyomma triste, the third most prevalent species in the environment. This tick species is a frequent human biter in both Uruguay and Argentina where it transmits a pathogen, Rickettsia parkeri, to humans.

Hosts mobility and spatial spread of Rickettsia rickettsii

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.

Complex systems as the Brazilian Spotted Fever (BSF), present challenges in terms of modeling and policy development. BSF human cases have 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 developed a reaction-diffusion system for the spread of BSF by considering the spatial structure and migration of amplifier hosts to gain a better understanding of the spatial spread of the R. rickettsii and potentially predict future epidemic outcomes. We performed stochastic simulations and numerical analysis to investigate the impact of potential interventions to mitigate the spatial spread of the disease. Our results indicate that as we vary the amount of capybaras’ food sources, the velocity at which the disease advances is roughly proportional to the carrying capacity, hence proportional to the local risk of zoonotic infection. Some geographical barriers, generated for example by riparian reforesting, can generate positive ecological impacts and can impede the spread of BSF to humans.

Amblyomma ticks infesting amphibians and Squamata reptiles from the lower Amazon region, Brazil

Amphibians and Squamata reptiles belonging to a zoological collection were screened for ectoparasites, which were removed from the hosts and identified using morphological keys. Descriptive statistics and analysis of the association between the parasite and host characteristics (taxonomic group, capture location and habitat) were done. Among the 1256 animals examined (319 amphibians and 937 reptiles), 86 individuals were parasitized, corresponding to a frequency of 6.9% (6.6% reptiles and 7.5% amphibians). Ticks in the adult and nymph stages were identified to the species level; all of them belonged to the species Amblyomma dissimile. The larvae were identified to the genus level and were all Amblyomma sp. In total 69 larvae, 28 nymphs and eight adults were found. The most parasitized species was the frog Rhinella major: 24 parasitized animals of 65 examined (36.9%). There was a difference (P < 0.001) between parasitism by ticks of the genus Amblyomma with regard to the habitat of capture of the parasitized animal, with a higher parasitism rate in hosts that inhabited open areas as compared to animals ensconced in forest areas and edges of forests. New tick-host associations are given.

Biological parameters of Amblyomma coelebs Neumann, 1906 (Acari: Ixodidae) under experimental conditions

Abstract One generation of Amblyomma coelebs life cycle under experimental conditions was evaluated. Ten tick pairs were allowed to feed on rabbits under laboratory conditions (LC), resulting six engorged females with a mean weight of 1,403.9 mg. Two females were maintained in a forest reserve under natural conditions (NC), and four were maintained in incubators (LC). The engorgement period lasted 10.33 days. Pre-oviposition periods were 10.75 (NC) and 22 days (LC). The mean egg-mass weight was 514.76 mg, and the blood meal conversion index was 36.67% (LC). Incubation period under NC and LC were 91 and 56.33 days and hatching rates were 50% and 28.33%, respectively. Larval engorgement period ranged from 4 to 10 days, with average weight of 1.1 mg. Engorged larvae were incubated under NC and LC, with a premolt period of 27 to 36 days and molting rate of 7.1% and 28.7%, respectively. Nymphal engorgement period ranged from 5 to 7 days, with a mean weight of 18.8 mg and a recovery rate of 54.54%. In LC, the ecdysis mean period was 24.5 days, and molting rate was 44.44%, resulting in 24 adult A. coelebs. Our results show a life cycle of 187.45 (NC) and 149 (LC) days.

CAPIVARAS (Hydrochoerus hydrochaeris) E A PRESENÇA DO CARRAPATO (Amblyomma sculptum) NO CAMPUS DA UFSCAR-ARARAS, SÃO PAULO

Resumo Capivaras são territoriais e vivem em grupos sociais, ocorrendo comumente em áreas antropizadas. Em algumas regiões do Brasil, estes animais apresentam infestação por carrapatos do gênero Amblyomma, que por sua vez são considerados como principal vetor biológico e reservatório natural da bactéria Rickettsia rickettsii, agente causador da Febre Maculosa Brasileira. Na UFSCar campus Araras, a interação entre capivaras, carrapatos e comunidade acadêmica é frequente, ocorrendo principalmente durante a estação seca. Este estudo teve como objetivo realizar um censo populacional das capivaras que ocupam o campus, identificando sua área de uso e se estes roedores se encontravam infestados por carrapatos. Realizou-se observação direta das capivaras, captura-marcação e recaptura com uso de um brete, e também coleta dos carrapatos nas capivaras e no ambiente. Registrou-se um total de 56 capivaras, com densidade de 1,50 ind./ha. Foram capturados 24 animais, sendo 25% machos e 75% fêmeas, dos quais 25% eram adultos, 45,8% jovens e 29,2% filhotes. A espécie de carrapato amplamente encontrada infestando tanto os animais como o ambiente foi A. sculptum. Conclui-se que o grupo de capivaras apresentou um número elevado de indivíduos por causa da abundância de recursos e ausência de predadores, e também com grande infestação por carrapatos.

Off-host development and survival of Rhipicephalus (Boophilus) microplus in the Brazilian semiarid

Rhipicephalus (Boophilus) microplus is the most economically important tick of the world, including Brazil. Whereas the epidemiology of R. microplus is well known in most of the Brazilian land, virtually nothing is known from the Brazilian semiarid region, the Caatinga biome. Considering the relevance of R. microplus for the cattle industry within the Caatinga, this study aimed to evaluate for the first time the off-host development of this tick species under natural conditions of the Caatinga. During 2011-2015, engorged females of R. microplus were exposed to field conditions of native Caatinga, where female oviposition, egg incubation and hatching, and larval survival were quantified. In parallel, counterpart ticks (control group) were evaluated under optimal conditions in the laboratory. During the study, nearly 100% of the engorged females of the control group successfully oviposited fertile egg masses, from which most of the eggs yielded larvae (mean % hatching usually>90%). Under field conditions, while almost 100% of the engorged females oviposited, in most of the times no larvae hatched from these eggs. Furthermore, when larvae hatched, mean % hatching was most of the times <50%. Soil temperatures did not oscillate drastically through the study, with mean temperature between 30 and 35°C in most of the time. In contrast, rainfall was irregular throughout the study. Correlation analyses indicated that either the number of egg masses that yielded larvae, or the mean % hatching of the egg masses were positively associated with higher rainfall months. Our results showed that in most of the time, field conditions were unfavorable for R. microplus, indicating that cattle would have a low exposure to R. microplus infestations when raised in Caatinga fields like those of the present study.

Transmission dynamics and control of Rickettsia rickettsii in populations of Hydrochoerus hydrochaeris and Amblyomma sculptum

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.

Ecology and genetic variation of Amblyomma tonelliae in Argentina

The ecology of Amblyomma tonelliae (Ixodida: Ixodidae), including its seasonal distribution and the development periods of each stage, was investigated during a study carried out over two consecutive years in northwestern Argentina. In addition, the genetic variation of this tick was studied through analyses of 16S rDNA sequences. Amblyomma tonelliae has a 1-year lifecycle characterized by a long pre-moult period in larvae with no development of morphogenetic diapause. Larvae peak in abundance during late autumn and early winter; nymphs peak in abundance in spring, and adults do so from late spring to early summer. Amblyomma tonelliae shows a marked ecological preference for the driest areas of the Chaco ecoregion. In analyses of 16S rDNA sequences in genes from different populations of A. tonelliae, values for nucleotide diversity and the average number of nucleotide differences showed genetic diversity within this species to be low. No significant differences were found in comparisons among populations.

Vector potential and population dynamics for Amblyomma inornatum

We studied the natural life cycle of Amblyomma inornatum and its vector potential in South Texas. This tick is distributed throughout South Texas and most of Central America. A. inornatum represented 1.91% of the ticks collected by carbon dioxide traps during a study of free-living ticks in the Tamaulipan Biotic Province in South Texas. The life cycle of A. inornatum in South Texas showed a clear seasonal pattern consistent with one generation per year. Nymphs emerged in the spring with a peak in February through May. Adults emerged in the summer with a peak in July through September. Detection of A. inornatum larvae was negatively correlated with saturation deficit and positively correlated with rain in the previous few months. Adult activity was positively correlated with temperature and rain in the previous five weeks. Using PCR we detected the presence of species related to Candidatus Borrelia lonestari, Borrelia burgdorferi, Rickettsia species (Candidatus Rickettsia amblyommii), Ehrlichia chaffeensis, and another Ehrlichia related to Ehrlichia ewingii. Finally we sequenced the mitochondrial 16S rRNA genes and found that A. inornatum is most closely related to Amblyomma parvum. This is the first report of the life cycle, vector potential and phylogeny of A. inornatum.

Complementary data on four methods for sampling free-living ticks in the Brazilian Pantanal

In this study, four methods for sampling free-living ticks that are used in ecological and human tick-bite risk studies were evaluated. Cloth dragging, carbon dioxide traps and visual searches and inspection of plant litter on the ground were used in field and forest areas within the Brazilian Pantanal. Among the three tick species collected, Amblyomma sculptum predominated, followed by Amblyomma parvum and Amblyomma ovale. Dragging, a cheap and simple technique, yielded the highest numbers of ticks, particularly nymphs. The visual search detected a high number of adult ticks and provided information on tick questing height. Even though laborious, plant litter examination showed that large numbers of ticks may use this stratum. Carbon dioxide (CO2) traps are expensive and difficult to handle, but they are highly efficient for adult ticks, especially A. parvum. These data indicate that one method alone is incapable of providing a representative sample of the tick fauna in a particular area and that multiple techniques should be used for tick population studies.

Environmental infestation and rickettsial infection in ticks in an area endemic for Brazilian spotted fever

Brazilian spotted fever (BSF), caused by Rickettsia rickettsii, is endemic in the municipality of Americana, southeastern Brazil, where the disease is transmitted by the tick Amblyomma cajennense. This study evaluated the tick fauna and rickettsial infection in free-living ticks that were captured monthly using dry ice traps in areas endemic for BSF in Americana, from July 2009 to June 2010. Two tick species were captured: A. cajennense (6,122 larvae; 4,265 nymphs; 2,355 adults) and Amblyomma dubitatum (7,814 larvae; 3,364 nymphs; 1,193 adults). The immature stages of A. cajennense and A. dubitatum had similar distribution through the 12-month period, with larvae of both species collected in highest numbers between April and July, and nymphs between June and October. The highest numbers of A. cajennense adults were collected between October and December, whereas A. dubitatum adults were collected in relatively similar numbers throughout the 12-month period. Rickettsial infection was evaluated by means of PCR in 1,157 A. cajennense and 1,040 A. dubitatum ticks; only 41 (3.9%) A. dubitatum were found to be infected by Rickettsia bellii. The present study showed that the areas of Americana that are endemic for BSF are characterized by high environmental burdens of A. cajennense and A. dubitatum.

Ecology, biology and distribution of spotted-fever tick vectors in Brazil

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.

Host-Parasite Relationship of Ticks (Acari: Ixodidae and Argasidae) and Feral Pigs (Sus scrofa) in the Nhecolândia Region of the Pantanal Wetlands in Mato Grosso do Sul

Feral pigs (S. scrofa) were introduced to the Pantanal region around 200 years ago and the population appears to be in expansion. Its eradication is considered to be impossible. The population of feral pigs in the Pantanal wetlands is currently estimated at one million. Two scientific excursions were organized. The first was conducted during the dry season, when 21 feral pigs were captured and the second was during the wet season, when 23 feral pigs were captured. Ticks were collected and the oviposition and hatching process were studied to confirm the biological success of each tick species. Three tick species were found to be feeding on feral pigs: Amblyomma cajennense, A. parvum, and Ornithodoros rostratus. During the dry season, 178 adult A. cajennense were collected, contrasting with 127 A. cajennense specimens in the wet season. This suggests that the seasonality of these ticks in the Brazilian Pantanal wetlands could be different from other regions. The results indicate that A. parvum and A. cajennense are biologically successful parasites in relation to feral pigs. A. cajennense appears to have adapted to this tick-host relationship, as well as the areas where feral pigs are abundant, and could play a role in the amplification of this tick population.

Meteorological indicators for Amblyomma cajennense and population dynamics in the Tamaulipan Biotic Province in Texas

We studied the population dynamics of free-living ticks in the Tamaulipan Biotic Province in south Texas from March, 2005 to November, 2008. We collected 70,873 ticks using carbon dioxide traps. Amblyomma cajennense represented 93.6% of the ticks identified. A. cajennense is distributed from northern Argentina to south Texas in the Tamaulipan Biotic Province. Emergence of larval A. cajennense ticks was observed two to five weeks after significant rain events (p<0.0001) and had a strong negative correlation with temperature (p<0.0001). More larvae were observed under humid conditions (p<0.05). Fewer larvae were observed during windy and warmer conditions (p<0.05). This observation indicates high sensitivity of larvae to desiccating conditions. Peaks in nymphal activity were observed after peaks of larval emergence. Activity of nymphs was negatively correlated with temperature (p<0.05). Adult activity was negatively correlated with humidity (p<0.05) and negatively correlated with total rain from three to six weeks prior to observation (p<0.05). Adult A. cajennense are particularly tolerant to drier conditions relative to other closely related ticks. Adult female activity was positively correlated with temperature (p<0.05). Peaks in rain activity and a summer behavioral diapause appear to be the dominant factors controlling emergence of larvae, and by extension, the life cycle of A. cajennense in the Tamaulipan Biotic Province.

Ticks (Acari: Ixodidae) within various phytophysiognomies of a Cerrado reserve in Uberlândia, Minas Gerais, Brazil

Cerrado biome, the South American savannah, covers about 2 million km(2) and is very rich in endemic species but threatened by agriculture. In this report free-living tick species are presented, and their seasonal and relative distribution within the various phytophysiognomies in a small Cerrado reserve in Minas Gerais State, Brazil. Overall 2,694 free-living ticks were found during a 2 years sampling period with CO(2) traps and cloth dragging. Of these, 73.5% were Amblyomma cajennense and 0.6% Amblyomma dubitatum. All other ticks (25.9%) were retained as Amblyomma spp. Adults of A. cajennense peaked in spring, the nymphs in winter of both years. Amblyomma larval clusters were found in autumn and winter. Adult ticks (46.7%) and nymphs (39.5%) were most often found in woodlands, whereas most larval clusters were found in valley-side marshes (39%). Amblyomma cajennense, Anocentor nitens, Rhipicephalus (Boophilus) microplusand Rhipicephalus sanguineus ticks were found on domestic animals from neighboring properties. Search for Rickettsia in the hemolymph of 497 A. cajennense and one A. dubitatum ticks yielded negative results. Results confirmed earlier reports on the overwhelming prevalence of A. cajennense ticks in the Cerrado biome of Brazil and added information to habitat preferences of this tick species, a major vector in Brazil of the Rocky Mountain spotted fever.

Notes on population dynamics of Amblyomma ticks (Acari: Ixodidae) in Brazil

Previous population dynamics data, generated for Amblyomma parvum Aragão and Amblyomma cajennense (Fabricius) in Argentina and southeastern Brazil, have indicated that these ticks complete 1 generation per year, with larvae predominating in autumn, nymphs in winter, and mostly adults during spring and summer. The present study reports population dynamics data for free-living Amblyomma spp. ticks in northern Brazil (Amazon forest, latitude 10 degrees S, 63 degrees W), and for Amblyomma spp. ticks collected on birds in southeastern Brazil (latitude 23 degrees S, 45 degrees W). In northern Brazil, adult ticks predominated from mid-spring to mid-autumn, larvae predominated in early winter, and nymphs from mid-winter to mid-spring. Seven Amblyomma spp. were identified, although A. cajennense predominated in 1 of the 2 sites sampled. In southeastern Brazil, larval infestations on birds peaked in autumn, followed by a nymphal infestation peak in late winter. At least 32% and 75% of these larvae and nymphs, respectively, were identified as Amblyomma longirostre (Koch). Similar to previous work, the present study showed that Amblyomma spp. larvae and nymphs predominated during autumn-winter months, and mostly adults during spring-summer months, a pattern compatible with 1 generation/yr, even at latitude 10 degrees S in northern Brazil.

Influence of photoperiod and temperature on the larval behavioral diapause of Amblyomma cajennense (Acari: Ixodidae)

Larval behavioral diapause was shown to be the major factor controlling the 1-yr generation pattern of Amblyomma cajennense (F.) (Acari: Ixodidae) in Brazil. During fieldwork, this behavior was shown to coincide with long daylength (>12 h) and high mean ground temperature (approximately =25 degrees C), which prevail during spring-summer in Brazil. The current study evaluated biological parameters of engorged females, their eggs, and the resultant larvae inside plastic pots planted with the grass Brachiaria decumbens Stapf. held in incubators set with different combinations of temperature and photoperiod. Both the long daylength (photoperiod 14:10 [L:D] h) and high temperature (25 degrees C) during larval hatching induced larval behavioral diapause, characterized by the confinement of hatched larvae on the ground below the vegetation for many weeks. When long daylength was present during hatching, but temperature was low (15 degrees C), larvae did not enter diapause. Similarly, when short daylength (10:14 or 12:12) was present during larval hatching, larvae did not enter diapause regardless whether temperature was high (25 degrees C). Termination of diapause was induced by shifting photoperiod from 14:10 to 12:12 or the temperature from 25 to 15 degrees C. When applied to field conditions, the present results indicate that both high ground mean temperature (approximately =25 degrees C) and long daylength (>12 h) during spring-summer (October-March) are responsible for the induction and maintenance of A. cajennense larval behavioral diapause in the field. Furthermore, both the low ground mean temperature (approximately 20 degrees C) and the short daylength (<12 h) during autumn (April-May) are responsible for termination of larval behavioral diapause in the field.

Tick fauna from two locations in the Brazilian savannah

The Cerrado is Brazil's tropical savannah, which is arguably under greater threat than the Amazon rainforest. The Cerrado Biome of tropical South America covers about 2 million km(2) and is considered a biodiversity hot spot which means that it is especially rich in endemic species and particularly threatened by human activities. The Cerrado is increasingly exposed to agricultural activities which enhance the likelihood of mixing parasites from rural, urban and wildlife areas. Information about ticks from the Cerrado biome is scarce. In this report tick species free-living, on domestic animals and on a few wild animals in two farms in the Cerrado biome (Nova Crixás and Araguapaz municipalities, Goiás State, Brazil) are described. Amblyomma cajennense was the first and Amblyomma parvum the second host-seeking tick species found. Only two other tick species were found free-living: one Amblyomma nodosum and three Amblyomma naponense nymphs. Cattle were infested with Boophilus microplus and A. cajennense. Buffalos were infested with B. microplus and A. parvum. Dogs were infested with A. cajennense, Amblyomma ovale, A. parvum and Rhipicephalus sanguineus ticks. Anocentor nitens, B. microplus, A. cajennense, and A. parvum were found on horses. Amblyomma auricularium were found attached to nine-banded armadillos and Amblyomma rotundatum to red-footed tortoise, cururu toads and a rattlesnake. The latter was also infested with an adult A. cajennense. No tick was found on a goat, a tropical rat snake and a yellow armadillo. Among the observations the infestation of several domestic animals with A. parvum seems be the main feature. It suggests that this species might become a pest. However, the life cycle of A. parvum in nature, as well as its disease vectoring capacity, are largely unknown. It would be important to determine if it is a species expanding its geographic range by adaptation to new hosts or if it has been maintained in high numbers at definite locations by specific and still undetermined conditions. A higher prevalence of A. cajennense in most Brazilian biomes, with the exception of rainforests, was already shown before. Thus this species is favored by deforestation and is an important research target as it is the most common vector associated with the Brazilian spotted fever.

Species diversity and seasonality of free-living ticks (Acari: Ixodidae) in the natural habitat of wild Marsh deer (Blastocerus dichotomus) in Southeastern Brazil

This study evaluated the presence and seasonal activity of free-living ticks in remaining marsh areas by the Paraná river, in Brazil. Eight field trips (once per season) for collection of ticks were performed during 2 years. Using CO2 traps, dragging, and visual inspection of vegetation, five free-living tick species were collected, in the following order of abundance: Amblyomma cajennense, Amblyomma dubitatum, Amblyomma triste, Amblyomma coelebs, and Amblyomma nodosum. The seasonal pattern of A. cajennense was characterized by the highest peaks for adult ticks in the summer/spring months, for nymphs in the winter and for larvae in the autumn and winter. A. dubitatum and A. triste presented similar seasonal patterns characterized by peaks of adult ticks in the autumn. Nymphs of A. dubitatum peaked in the winter of the first year and in the winter/spring of the second year. A. triste was the only species to be collected in significantly higher numbers in the marsh than in surrounding drier areas such as forest patches. Among domestic animals living close the marsh areas, horses were infested by Anocentor nitens, A. cajennense, and Boophilus microplus, bovines were infested solely by B. microplus, and dogs were infested by Rhipicephalus sanguineus. Adults of A. triste showed to be well adapted to the marsh environment. This result, at least partially, explains local previous observations on the association of A. triste with marsh deer, as this vertebrate host inhabits mainly the marsh area.

Relationship between glutathione S-transferase, catalase, oxygen consumption, lipid peroxidation and oxidative stress in eggs and larvae of Boophilus microplus (Acarina: Ixodidae)

Glutathione S-transferases (GSTs) are enzymes that act in excretion of physiologic and xenobiotic substances, protecting cells against chemical toxicity and stress. In this work, we characterized the enzymatic activity of GST in eggs and larvae of cattle tick Boophilus microplus, on different days after oviposition and eclosion. The results showed that the GST activity varied depending on the time elapsed after oviposition and eclosion. Molecules involved in mechanism of protection from oxidative stress are correlated with the increase in GST activity. The oxygen consumption kinetics showed a positive correlation with the increase in GST activity during embryogenesis. A high content of thiobarbituric acid reactive substances were observed in egg and larva extracts, indicating that ticks face high oxidative stress during embryogenesis and aging. In eggs and larvae, GST activity can be correlated to kinetic parameters of oxidative stress such as catalase and glutathione. In addition, GST activity showed strong positive correlation with lipid peroxidation, an indication that it plays a role in oxidant defences in eggs.

Study of the seasonal dynamics, life cycle, and host specificity of Amblyomma aureolatum (Acari: Ixodidae)

In the first part of this study, monthly infestation by ticks was evaluated on dogs from December 2000 to November 2002 in the rural area of Taiaçupeba, São Paulo. Adults of Amblyomma aureolatum (Pallas) were found on dogs in all months, with a mean prevalence per month of 46.9 +/- 15.7% (range, 25-80%). The mean tick relative abundance per month was 2.4 +/- 2.7 ticks (range, 0.5-14 ticks), and the mean tick mean intensity per month was 4.7 +/- 4.2 ticks (range, 1.5-23.3 ticks). No A. aureolatum immature ticks were found on dogs. In the second part of this study, we studied the life cycle of A. aureolatum in the laboratory. We tested the suitability of six host species for the immature stages and dogs for the adult stage. Tick developmental periods were observed at different temperatures (23, 25, or 27 degrees C), always with RH >95%, which were satisfactory for all free-living developmental stages of the tick life cycle. Chickens and guinea pigs were the most suitable hosts for larvae and nymphs (recovery rates, 18.4-52.2%). Dogs were highly suitable for adult ticks (all females exposed to them were recovered and laid eggs) but were unsuitable for the immature ticks (recovery rates, 0-10%). Based on published host records for A. aureolatum, our results indicate that dogs and birds are primary hosts for adult and immature stages, respectively, of A. aureolatum in nature. In addition, wild guinea pigs are indicated as another potential primary host for immature ticks.

Seasonal dynamics of the Cayenne tick, Amblyomma cajennense on horses in Brazil

The population dynamics of all stages of the Cayenne tick, Amblyomma cajennense (Fabricius) (Acari: Ixodidae) on horses was evaluated over a period of 2 years in the district of Pedro Leopoldo, State of Minas Gerais, Brazil. Every 14 days, the left side of 20 horses was brushed for collection of immature stages; counts of adults were also undertaken. Infestation by larvae was detected from April to August, whereas nymphs were observed from June to October. Infestation by adults was detected throughout the year, and the highest population density occurred from September to March. The number of males was always higher than the number of females, but with considerable reduction in the male : female ratio between April and July. It was observed that 25% of the horses carried 41% of the infesting ticks, and 20% carried only 10% of the ticks during the entire period of the study.