Molecular identification and morphological variations of Amblyomma lepidum imported to Egypt, with notes about its potential distribution under climate change.

The tick Amblyomma lepidum is an ectoparasite of veterinary importance due to its role in transmitting livestock diseases in Africa, including heartwater. This study was conducted in 2023 to monitor Amblyomma spp. infestation in dromedary camels imported from Somalia, Ethiopia, and Sudan to Egypt. This study inspected 200 camels at the Giza governorate's camel market that had been imported from Somalia, 200 from Ethiopia, and 200 from Sudan for tick infestation. Specimens were identified using morphological characteristics and phylogenetic analyses of the 12S and 16S rRNA genes. Clusters were calculated using an unweighted pair-group method with arithmetic averages (UPGMA) dendrogram to group the specimens according to their morphometric characteristics. The morphometric analysis compared the body shape of ticks collected from different countries by analyzing dorsal features. Principal component analysis (PCA) and canonical variate analysis (CVA) were performed to obtain body shape variation among specimens from different countries. Results indicated that camels were infested by 57 males Amblyomma lepidum, and no female specimens were observed; among these specimens, one may have a morphological abnormality. The results suggest that A. lepidum specimens collected from camels imported to Egypt from African countries exhibit locally adapted morphology with variations among specimens, particularly variations in body size. This adaptation suggests minimal potential for genetic divergence. Ecological niche modeling was used to predict the areas in Africa with suitable climates for A. lepidum. The study confirmed that East African countries might have the most favorable climatic conditions for A. lepidum to thrive. Interestingly, the amount of rain during the wettest quarter (Bio16) had the strongest influence on the tick's potential distribution, with suitability decreasing sharply as rainfall increased. Future predictions indicate that the climatic habitat suitability for A. lepidum will decrease under changing climate conditions. However, historical, current, and future predictions indicate no suitable climatic habitats for A. lepidum in Egypt. These findings demand continuous surveillance of A. lepidum in camel populations and the development of targeted strategies to manage tick infestations and prevent the spread of heartwater disease.

Phenology of five tick species in the central Great Plains.

The states of Kansas and Oklahoma, in the central Great Plains, lie at the western periphery of the geographic distributions of several tick species. As the focus of most research on ticks and tick-borne diseases has been on Lyme disease which commonly occurs in areas to the north and east, the ticks of this region have seen little research attention. Here, we report on the phenology and activity patterns shown by tick species observed at 10 sites across the two states and explore factors associated with abundance of all and life specific individuals of the dominant species. Ticks were collected in 2020-2022 using dragging, flagging and carbon-dioxide trapping techniques, designed to detect questing ticks. The dominant species was A. americanum (24098, 97%) followed by Dermacentor variabilis (370, 2%), D. albipictus (271, 1%), Ixodes scapularis (91, <1%) and A. maculatum (38, <1%). Amblyomma americanum, A. maculatum and D. variabilis were active in Spring and Summer, while D. albipictus and I. scapularis were active in Fall and Winter. Factors associated with numbers of individuals of A. americanum included day of year, habitat, and latitude. Similar associations were observed when abundance was examined by life-stage. Overall, the picture is one of broadly distributed tick species that shows seasonal limitations in the timing of their questing activity.

The first record of an established population of Amblyomma maculatum (Acari: Ixodidae) in New Jersey, USA.

Amblyomma maculatum Koch, the Gulf Coast tick, is expanding northward from its original range in the southeastern United States. In 2013, its most northern collection was in Delaware. Amblyomma maculatum has since been found in Connecticut, Illinois, and New York. It is the vector of the human pathogen Rickettsia parkeri, the causative agent of R. parkeri rickettsiosis. We report the first finding of an established population of A. maculatum in Salem County, NJ, with a R. parkeri infection prevalence rate of 23.8%. Our finding of A. maculatum is consistent with other recent findings in the northeastern United States in that specimens were found in open areas devoid of tree canopy. This discovery demonstrates the importance of tick surveillance in order to identify expanding tick populations and the pathogens they may transmit.

Effects of Piper aduncum (Piperales: Piperaceae) Essential Oil and Its Main Component Dillapiole on Detoxifying Enzymes and Acetylcholinesterase Activity of Amblyomma sculptum (Acari: Ixodidae).

Amblyomma sculptum is a species of tick in the family Ixodidae, with equids and capybaras among its preferred hosts. In this study, the acaricidal activity of the essential oil (EO) from Piper aduncum and its main component, Dillapiole, were evaluated against larvae of A. sculptum to establish lethal concentration values and assess the effects of these compounds on tick enzymes. Dillapiole exhibited slightly greater activity (LC50 = 3.38 mg/mL; 95% CI = 3.24 to 3.54) than P. aduncum EO (LC50 = 3.49 mg/mL; 95% CI = 3.36 to 3.62) against ticks. The activities of α-esterase (α-EST), ß-esterase (ß-EST), and glutathione-S-transferase (GST) enzymes in A. sculptum larvae treated with Dillapiole showed a significant increase compared to the control at all concentrations (LC5, LC25, LC50 and LC75), similar results were obtained with P. aduncum EO, except for α-EST, which did not differ from the control at the highest concentration (LC75). The results of the acetylcholinesterase (AChE) activity show an increase in enzyme activity at the two lower concentrations (LC5 and LC25) and a reduction in activity at the two higher, lethal concentrations (LC50 and LC75) compared to the control. These results suggest potential mechanisms of action for these natural acaricides and can provide guidance for the future development of potential plant-derived formulations.

Don't go chasing waterfalls: the phenology of Amblyomma americanum and increased collection of medically relevant ticks further away from hiking trails in the Piedmont of North Carolina, USA.

Hiking is a popular recreational activity in North Carolina that may expose people to ticks and tick-borne pathogens. However, there is a lack of knowledge on how ticks are distributed on and near trails. Our study tested the hypothesis that ticks are more likely to be encountered when moving further away from trails by measuring differences in relative abundance at various distances. We tested 4 distances (middle of trail, edge of trail, 5 m, 20 m), as well as an on-trail and off-trail grouping. We collected significantly more ticks and ticks were more likely to be collected at our 20 m and 5 m sampling distances rather than directly on or adjacent to trails, and significantly more were collected during off-trail collections than on-trails. When looking only at Amblyomma americanum, post hoc comparisons revealed that significantly more juvenile stages were collected at 5 m and 20 m distances, but not for adults. Our monthly sampling also allowed us to describe the phenology of A. americanum in North Carolina, which is consistent with the phenology of this species in the southeastern United States with adults peaking May-Jun, nymphs Jun-Jul, and larvae in Jul-Aug. These results generally demonstrate the importance of utilizing established trails when hiking to decrease tick-borne disease risk and should be communicated to the public as a recommendation for reducing tick-encounter risk.

New hard tick (Acari: Ixodidae) reports and detection of Rickettsia in ticks from Sierra Nevada de Santa Marta, Colombia.

The Sierra Nevada de Santa Marta (SNSM), located in northern Colombia, is considered a geographical island with high levels of biodiversity and endemism. However, little is known about tick species and their associated microorganisms at the SNSM. In this study we sampled host-seeking ticks in areas of the town of Minca within the SNSM. We collected 47 ticks identified as Amblyomma pacae, Amblyomma longirostre, Amblyomma ovale, Amblyomma mixtum, Haemaphysalis juxtakochi, Ixodes sp. cf. Ixodes affinis and Ixodes sp. Of these ticks, we tested for Rickettsia spp. by amplifying the gltA, SCA1, and 16S rRNA genes via PCR. Rickettsia amblyommatis was detected in one pool of 3 larvae and in a female of A. pacae. Additonally, we isolated Rickettsia sp. belonging to the group of spotted fevers in larvae of A. longirostre. This study reports new findings of six species of ticks and two species of Rickettsia within the SNSM.

Survey of Rickettsia spp. in ticks (Acari: Ixodidae) infesting opossums (Didelphis albiventris) and capybaras (Hydrochoerus hydrochaeris) from an urban park in southeastern Brazil.

Ticks are hematophagous arthropods and, during feeding, may transmit pathogens to vertebrate hosts, including humans. This study aimed to investigate the presence of Rickettsia spp. in ticks collected between 2010 and 2013 from free-ranging capybaras (Hydrochoerus hydrochaeris) and opossums (Didelphis albiventris) that inhabit Sabiá Park in Uberlândia, Brazil. Overall, 1,860 ticks were collected: 1,272 (68.4%) from capybaras (487 of the species Amblyomma sculptum, 475 adults and 12 nymphs; 778 Amblyomma dubitatum, 727 adults and 51 nymphs; and seven larva clusters of the genus Amblyomma); and 588 (31.6%) from opossums (21 A. sculptum, one adult and 20 nymphs; 79 A. dubitatum, all nymphs; 15 Ixodes loricatus, 12 adults and three nymphs; 457 Amblyomma sp. larva clusters; 15 Ixodes sp. larva clusters; and one Argasidae larva cluster). Out of 201 DNA samples tested for the presence of Rickettsia spp. DNA using polymerase chain reaction (PCR) 12 showed amplification of a gtlA gene segment that was specific to Rickettsia bellii, a bacterium non-pathogenic to humans. As there has been a report showing serological evidence of infections caused by Rickettsia species of the spotted fever group (SFG) in capybaras and opossums in the park, including Rickettsia rickettsii, the etiological agent of Brazilian spotted fever, and considering the presence of A. sculptum ticks, which are aggressive to humans, as well as these vertebrate hosts, which are amplifiers of R. rickettsii, it is important to monitor the presence of SFG rickettsiae in the Sabiá Park, which is visited daily by thousands of people.

High-resolution prediction models for Rhipicephalus microplus and Amblyomma cajennense s.l. ticks affecting cattle and their spatial distribution in continental Ecuador using bioclimatic factors.

In Ecuador, the main tick species affecting cattle are Rhipicephalus microplus and Amblyomma cajennense sensu lato. Understanding their spatial distribution is crucial. To assess their distribution, data from 2895 farms visited between 2012 and 2017 were utilized. Ticks were collected during animal inspections, with each farm's location georeferenced. Bioclimatic variables and vapor pressure deficit data were obtained from Climatologies at High resolution for the Earth´s Land Surface Areas (CHELSA) dataset. They were overlaid to develop predictive maps for each species using Random Forest (RF) models. The cross-validation results for RF prediction models showed high accuracy for both R. microplus and A. cajennense s.l. presence with values of accuracy = 0.97 and 0.98, sensitivity = 0.96 and 0.99, and specificity = 0.96 and 0.93, respectively. A carefully selected subset of bioclimatic variables was used to describe the presence of each tick species. Higher levels of precipitation had positive effect on the presence of R. microplus but a negative effect on A. cajennense s.l. In contrast, isothermality (BIO3) was more important for the presence of A. cajennense s.l. compared to R. microplus. As a result, R. microplus had a broader distribution across the country, while A. cajennense s.l. was mainly found in coastal areas with evident seasonality. The coexistence of both species in some regions could be attributed to transitional zones, whereas high altitudes limited tick presence. This information can aid in developing appropriate tick management plans, particularly considering A. cajennense s.l.'s broad host range species and R. microplus's specificity for cattle. Moreover, the predictive models can identify areas at risk of associated challenging hemoparasite, requiring special attention and mitigation measures.

Effective control of the motile stages of Amblyomma americanum and reduced Ehrlichia spp. prevalence in adults via permethrin treatment of white-tailed deer in coastal Connecticut, USA.

The lone star tick, Amblyomma americanum, is a common human-biting species whose range has been largely restricted to the southeastern United States, until recent detections of established populations on Long Island, New York and throughout coastal southern New England. We evaluated the effectiveness of topical treatment of 10 % permethrin delivered via 4-poster devices to white-tailed deer, Odocoileus virginianus, in the management of a newly discovered A. americanum population in Norwalk, Connecticut. Using a high-density deployment of one 4-poster device/12.7 ha, we were successful in significantly reducing densities of host-seeking adults (93 % reduction), nymphs (92 %), and larvae (96 %) from 2018 to 2020. We also documented a significant reduction (87 %) in parasitizing adults and nymphs on white-tailed deer from 2018 to 2019. The prevalence of Ehrlichia chaffeensis and Ehrlichia ewingii combined in host-seeking adults declined significantly from 47 % at the time the A. americanum population was discovered in 2017 to 7% in 2020. However, the prevalence in nymphs remained static (∼9%) throughout the study period. These data demonstrate that, when properly deployed in a density-dependent manner in terms of deer abundance, 4-poster devices can effectively manage parasitizing and host-seeking A. americanum populations and reduce the prevalence of two ehrlichial species of public health importance.

Established Population of the Gulf Coast Tick, Amblyomma maculatum (Acari: Ixodidae), Infected with Rickettsia parkeri (Rickettsiales: Rickettsiaceae), in Connecticut.

We identified an established population of the Gulf Coast tick (Amblyomma maculatum Koch) infected with Rickettsia parkeri in Connecticut, representing the northernmost range limit of this medically relevant tick species. Our finding highlights the importance of tick surveillance and public health challenges posed by geographic expansion of tick vectors and their pathogens.

Transcriptome analysis of Ehrlichia ruminantium in the ruminant host at the tick bite site and in the tick vector salivary glands.

Heartwater is a non-contagious tick-borne disease of domestic and wild ruminants. Data regarding the complex processes involved during pathogen-vector-host interaction during Ehrlichia ruminantium infection is lacking and could be improved with knowledge associated with gene expression changes in both the pathogen and the host. Thus, in the current study, we aimed to identify E. ruminantium genes that are up-regulated when the pathogen enters the host and before the disease is established. Identification of such genes/proteins may aid in future vaccine development strategies against heartwater. RNA-sequencing was used to identify E. ruminantium genes that were exclusively expressed at the tick bite site in sheep skin biopsies (SB) and in adult tick salivary glands (SG). RNA was extracted from pooled samples of the SB or SG collected at different time points during tick attachment and prior to disease manifestation. Ribosomal RNA (rRNA) was removed and the samples were sequenced. Several E. ruminantium genes were highly expressed in all the samples while others were exclusively expressed in each. It was concluded that E. ruminantium genes that were exclusively expressed in the SB or both SB and SG when compared to the transcriptome datasets from bovine elementary bodies (BovEBs) from cell culture may be considered as early antigenic targets of host immunity. In silico immunogenic epitope prediction analysis and preliminary characterization of selected genes in vitro using ELIspot assay showed that they could possibly be ideal targets for future vaccine development against heartwater, however, further epitope characterization is still required.

Validating Species Distribution Models With Standardized Surveys for Ixodid Ticks in Mainland Florida.

Tick-borne pathogens are of growing concern. The U.S. Centers for Disease Control and Prevention (CDC) developed guidelines standardizing surveys of tick vectors to better monitor the changes in their occurrences. Unbiased surveillance data, from standardized surveys, are presumed critical to generate valid species distribution models (SDMs). We tested previously generated SDMs from standardized protocols for three medically important ticks [Amblyomma americanum (Linnaeus, Ixodida, Ixodidae), Ixodes scapularis (Say, Ixodida, Ixodidae), and Dermacentor variabilis (Say, Ixodida, Ixodidae)]. These previous models ruled out a quarter to half of the state as having these species, with consensus occurrence in about a quarter of the state. New surveys performed throughout 2019 on 250 transects at 43 sites indicated the rule-out functions were 100% accurate for I. scapularis and D. variabilis and 91.9% for A. americanum. As SDM concordance increased, the proportion of transects yielding ticks increased. Independent surveys of SDMs provide external validation-an aspect missing from many SDM studies.

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.

Rickettsia amblyommatis isolated from Amblyomma mixtum (Acari: Ixodida) from two sites in Panama.

Rickettsia amblyommatis is widely distributed in the Americas, and has been reported to infect different species of ticks within its distribution. In Panama, R. amblyommatis is the most common Rickettsia and its presence was molecularly detected in nine species of ticks and one flea species. This work described the isolation of R. amblyommatis in Vero cells by shell vial technique, from Amblyomma mixtum ticks collected from a captive tapir from Gamboa (Colon province), and a horse from El Valle de Antón (Cocle province). These represent the first isolations of R. amblyommatis in Panama.

Low Abundance of Three Tick Species in the Piedmont of North Carolina.

Multiple species of ticks, including Ixodes scapularis (Say, Ixodida:Ixodidae), Amblyomma americanum (L., Ixodida:Ixodidae), and Dermacentor variabilis (Say, Ixodida:Ixodidae), occur in high and increasing abundance in both the northeast and southeast United States. North Carolina is at the nexus of spread of these species, with high occurrence and abundance of I. scapularis to the north and A. americanum to the south. Despite this, there are few records of these species in the Piedmont of North Carolina, including the greater Charlotte metropolitan area. Here, we update the known occurrence and abundance of these species in the North Carolina Piedmont. We surveyed for ticks using cloth drags, CO2 traps, and leaf litter samples at a total of 79 sites within five locations: Mecklenburg County, South Mountains State Park, Stone Mountain State Park, Duke Forest, and Morrow Mountain State Park, all in North Carolina, during the late spring, summer, and fall seasons of 2019. From these surveys, we had only 20 tick captures, illuminating the surprisingly low abundance of ticks in this region of North Carolina. Our results indicate the possibility of underlying habitat and host factors limiting tick distribution and abundance in the North Carolina Piedmont.

Rickettsia spp. and Ehrlichia spp. in Amblyomma ticks parasitizing wild amphibious sea kraits and yellow-margined box turtles in Okinawa, Japan.

Recently, several tick-borne pathogens were detected in reptile-associated ticks. However, studies on the microorganisms in reptile-associated ticks in Japan are limited. This molecular survey thus aimed to identify and characterize tick-borne pathogens (Rickettsiaceae and Anaplasmataceae) in reptile-associated ticks in Japan. In total, 77 Amblyomma nitidum and 104 Amblyomma geoemydae were collected from wild amphibious sea kraits (Laticauda semifasciata, Laticauda colubrina, and Laticauda laticaudata) and from yellow-margined box turtles (Cuora flavomarginata evelynae), respectively. Conventional polymerase chain reaction was performed using the DNA extracted from the ticks to detect the selected pathogens. Sequencing analysis of four Rickettsia genes (gltA, ompA, ompB, and sca4) led to the identification of a putative novel Rickettsia sp. and Rickettsia aeschlimannii-like rickettsia in A. nitidum and A. geoemydae, respectively. Sequencing analysis of gltA and groEL of Anaplasmataceae revealed that the Ehrlichia spp. in these ticks were novel and related to Candidatus Ehrlichia occidentalis. This is the first study on the microorganisms in A. nitidium and the first record of Rickettsia and Ehrlichia in A. geoemydae. Further studies are required to understand their pathogenicity to humans and animals and their life cycle in the wild.

Morphological and molecular characterization supporting Amblyomma mixtum presence in Cuba.

Amblyomma cajennense Fabricius, 1787 (Acari: Ixodidae) is a widely distributed tick taxon. Recent studies have reassessed this taxon as a complex of six species. Amblyomma mixtum Koch, 1844 has been suggested by some authors as the only species of this complex that is present in Cuba. Other authors have pointed a niche overlapping for A. mixtum and A. cajennense s.s. in the country. Detailed taxonomic studies on the Cuban species belonging to this complex are needed in order to evaluate their current distribution according to the recent classification. This study aimed to characterize Cuban populations from the A. cajennense complex by using tick samples obtained from 3 occidental provinces and 1 central province of the country. Morphological identification and measurements of the main relevant taxonomic structures were conducted by using Scanning Electron Microscopy. Phylogenetic analyzes were carried out with 16S ribosomal RNA, internal transcribed spacer 2 and the subunit I of mitochondrial cytochrome c oxidase gene sequences. The results of these studies demonstrated that all samples belonged to the species A. mixtum (Koch, 1844). This study constitutes the first molecular characterization of this Amblyomma species in Cuba. Further studies will be necessary in order to corroborate if A. cajennense s.s. is also present in the island.

Molecular phylogeny of Amblyomma exornatum and Amblyomma transversale, with reinstatement of the genus Africaniella (Acari: Ixodidae) for the latter.

The phylogeny of the hard tick genus Amblyomma Koch, 1844 deserves special attention, because several poorly studied tick species associated with reptiles still bear the name of this genus, although they may not belong to it. This study focuses on the phylogeny of two such species with uncertain taxonomic status, i.e., Amblyomma transversale (Lucas, 1845) and Amblyomma exornatum Koch, 1844, analyzing two mitochondrial (cytochrome c oxidase subunit 1 and 16S rRNA) and two nuclear (18S and 28S rRNA) genes. In the cox1 phylogenetic analysis, both Am. transversale and Am. exornatum were part of a sister group to all other Metastriata, whereas in the 16S rRNA gene analysis, Am. transversale belonged to a sister group to three subfamilies (Amblyomminae Neumann, 1911; Haemaphysalinae Hoogstraal and Aeschlimann, 1982; Bothriocrotoninae Klompen, Dobson and Baker, 2002), and Am. exornatum formed a sister group to other Amblyomminae. However, based on the 18S and 28S rRNA genes, Am. transversale belonged to a sister group of either Bothriocrotoninae alone or of both Bothriocrotoninae and Haemaphysalinae, respectively. In the latter two phylogenetic analyses Am. exornatum always clustered within Amblyomminae. Morphological comparisons revealed that Am. transversale has at least four unique characters and shares a high number of traits with the genera Robertsicus Barker and Burger, 2018 and Archaeocroton Barker and Burger, 2018, as well as with the subgenus Alloceraea Schulze, 1918 (represented by Haemaphysalis inermis Birula, 1895). These results justify that the genus Africaniella Travassos Dias, 1974 should be reinstated, and the species name of Am. transversale should be used as Africaniella transversale (Lucas, 1845).

Molecular detection of a Borrelia sp. in nymphs of Amblyomma brasiliense ticks (Acari: Ixodidae) from Iguaçu National Park, Brazil, genetically related to Borrelia from Ethiopia and Côte d'Ivoire.

Gram-negative spirochetes of the genus Borrelia are transmitted to vertebrate hosts through the tick bite during blood intake. Pathogenic Borrelia species may cause relapsing fever or Lyme borreliosis in humans. Our study aimed to molecularly detect and characterize bacteria of this genus in ticks collected in the Iguaçu National Park, located in southern Brazil. Ticks were collected from the environment (free living) and from hosts from May 2015 to July 2017. In total, 829 ticks were tested, being 741 from the environment and 88 from hosts; 128 ticks were larvae, 523 were nymphs, and 178 were adults (80 males and 98 females). The species identified were: Amblyomma brasiliense (42.9 %), Amblyomma coelebs (16.8 %), Amblyomma sp. (15.0 %), Amblyomma incisum (10.3 %), Amblyomma ovale (8.7 %), Haemaphysalis juxtakochi (5.5 %), Rhipicephalus microplus (0.5 %), Amblyomma longirostre (0.2 %), and Rhipicephalus sanguineus sensu lato (0.1 %). DNA extraction was performed with pools of larvae or nymphs, or individually with adults, for a total of 394 samples. The PCR technique used to detect Borrelia DNA was performed with two rounds of amplification reactions targeting a segment of the flagellin B gene (flaB). Amplification occurred in only one DNA sample, which was obtained from nymphs of A. brasiliense collected from the vegetation of a trail. The nucleotide sequence analysis revealed 90.8 % identity to a sequence of Borrelia sp. from Côte d'Ivoire, and 89.1 % identity to a sequence from Ethiopia. Phylogenetic analysis revealed that the Borrelia sequence from A. brasiliense was distinct from the Borrelia species of the groups belonging to Lyme borreliosis, relapsing fever and the one associated with reptile and echidna as hosts. The sequence is likely from a putative new species of Borrelia and was detected for the first time in A. brasiliense ticks.

Capybaras (Hydrochoerus hydrochaeris) as amplifying hosts of Rickettsia rickettsii to Amblyomma sculptum ticks: Evaluation during primary and subsequent exposures to R. rickettsii infection.

Rickettsia rickettsii is the agent of Brazilian spotted fever (BSF), the most lethal tick-borne disease in the western hemisphere. Amblyomma sculptum is the main vector of R. rickettsii in southeastern Brazil. Capybaras act as primary hosts for this tick species, and as amplifying hosts for R. rickettsii, creating new infected lineages of A. sculptum in BSF-endemic areas. In a recent study, we demonstrated that capybaras successively exposed to R. rickettsii-infected A. sculptum ticks developed a mean rickettsemic period of 9.2 days during primary infection, but no rickettsemia during subsequent expositions, when capybaras were immune to R. rickettsii. During the primary and subsequent infections, capybaras were also infested with uninfected A. sculptum ticks. These infestations compose the present study, which aimed to evaluate: (i) if either rickettsemic or non-rickettsemic capybaras could serve as infection sources of R. rickettsii for A. sculptum larvae and nymphs; (ii) the vector competence of the subsequent nymphs and adults (molted from the engorged ticks collected from capybaras); and (iii) if there were R. rickettsii-acquisition by uninfected ticks co-feeding with infected ticks on immune capybaras (without rickettsemia). Through experimental infection of capybaras with R. rickettsii via tick feeding, simulating a natural condition, we demonstrated that primarily infected capybaras developed rickettsemia that resulted in successful acquisition feeding of larvae and nymphs of A. sculptum, since part of these ticks maintained R. rickettsii transstadially, and the resultant molted ticks (either nymphs or adults) successfully transmitted the bacterium by feeding on susceptible rabbits. Contrastingly, all rabbit infestations with ticks derived from acquisition feeding on R. rickettsii-immune capybaras (including when acquisition ticks fed in direct contact with donor ticks) evidenced absence of R. rickettsii transmission due to lack of clinical signs and antibody response in those rabbits. Our results indicate that capybaras could serve as R. rickettsii-amplifying hosts for A. sculptum ticks only during the capybara's primary infection, but not during subsequent infections on immune capybaras. Finally, the probable co-feeding nonsystemic transmission of R. rickettsii seems to be irrelevant in the context of BSF epidemiology, in areas where capybaras are incriminated as main amplifying hosts of R. rickettsii for A. sculptum ticks.