Pathogenic potential of a Costa Rican strain of 'Candidatus Rickettsia amblyommii' in guinea pigs (Cavia porcellus) and protective immunity against Rickettsia rickettsii

Surveillance of ticks (Acari: Ixodidae) and tick-borne pathogens in Eastern Central Alabama

Similar to other states in the southeastern United States, human cases of tick-borne diseases in Alabama have risen steadily over the last 2 decades. Nevertheless, limited data have been published on ticks or tick-borne pathogen (TBP) distributions since the 1990s. To better understand the risk of tick and TBP exposure in eastern central Alabama, ticks were sampled repeatedly across 8 sites associated with recreational use during May and June of 2015 to characterize tick density and diversity. Although habitats were similar across sites, tick density varied among locations. Seven species were collected, but 97.7% of 1,310 samples were the lone star tick, Amblyomma americanum (L.), the primary vector of ehrlichial agents and the tick species most commonly linked to alpha-gal syndrome and southern tick-associated rash illness. To investigate pathogen prevalence among sites, we tested A. americanum by a multiplex qPCR assay for 5 bacterial species, including 3 Ehrlichia spp. and 2 Rickettsia spp. None of the specimens tested positive for Panola Mountain Ehrlichia or Rickettsia parkeri. However, causative agents of human ehrlichiosis, Ehrlichia chaffeensis and Ehrlichia ewingii, occurred at half of the locations with, respectively, 0.27% and 0.45% of A. americanum infected on average. In contrast, Rickettsia amblyommatis, a tick endosymbiont suspected to be nonpathogenic, was found in 54.5% of the 1119 A. americanum tested. Despite low infection rates of Ehrlichia spp. in A. americanum, high encounter rates with this species in recreational deciduous woodlands suggest a moderate risk of tick bite and a low-to-moderate risk of TBP exposure in late spring.

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.

Molecular screening of tick-borne microorganisms in ticks from rural areas of Panama, with the first record of Ehrlichia minasensis in Rhipicephalus microplus from Central America

During a molecular screening of rickettsial, borrelial and protozoal agents in ticks from rural areas of Panama, we detected DNA of Rickettsia amblyommatis in four Amblyomma mixtum collected from horses in a locality in Los Santos province. Ehrlichia minasensis and Anaplasma marginale were identified from three and two Rhipicephalus microplus, respectively, collected on cows from Chiriqui province. No DNA from other tick-borne agents was found. These results increase the information of R. amblyommatis and A. marginale in Panama, and also mark the first record of E. minasensis in Central America.

Optimization of artificial membrane feeding system for lone star ticks, Amblyomma americanum (Acari: Ixodidae), and experimental infection with Rickettsia amblyommatis (Rickettsiales: Rickettsiaceae)

With the introduction of siliconized artificial membranes, various artificial feeding systems (AFS) for hard ticks (Ixodidae) have been developed over the last decades. Most AFS utilize similar core components but employ diverse approaches, materials, and experimental conditions. Published work describes different combinations of the core components without experimental optimizations for the artificial feeding of different tick species. Amblyomma americanum L., (Acari: Ixodidae) (lone star tick) is a known vector and reservoir for diverse tick-borne pathogens, such as Rickettsia amblyommatis and Ehrlichia chaffeensis. Ongoing environmental changes have supported the expansion of A. americanum into new habitats, contributing to increased tick-borne diseases in endemic areas. However, a significant knowledge gap exists in understanding the underlying mechanisms involved in A. americanum interactions with tick-borne pathogens. Here, we performed a systematic analysis and developed an optimized AFS for nymphal lone star ticks. Our results demonstrate that Goldbeater's membranes, rabbit hair, hair extract, and adult lone star ticks significantly improved the attachment rate of nymphal ticks, whereas tick frass and frass extract did not. With the optimized conditions, we achieved an attachment rate of 46 ± 3% and a success rate of 100% (i.e., one or more attached ticks) in each feeding experiment for nymphal lone star ticks. When fed on sheep blood spiked with R. amblyommatis, both nymphal and adult lone star ticks acquired and maintained R. amblyommatis, demonstrating the feasibility of studying A. americanum-pathogen interactions using AFS. Our study can serve as a roadmap to optimize and improve AFS for other medically relevant tick species.

Distribution of different Rickettsia species in countries of the WHO Eastern Mediterranean (WHO-EMRO) region: An overview

SUBJECT

Rickettsia is a zoonotic bacterial pathogen transmitted by vectors and has extensive reservoirs in animal and human populations. Rickettsiosis is a public health problem all over the world. However, comprehensive information on the geographical distribution of different Rickettsia species, infection status of reservoirs, vectors, and human cases is lacking in most parts of the world. Therefore, this study aimed to investigate the geographical distribution of different Rickettsia species and their vectors in countries of the WHO-EMRO region.

METHODS

In this review study, a search was conducted for reports and published studies on Rickettsia species from WHO-EMRO region countries in various databases from 1995 to 2022. Finally, the reported status of human cases, reservoirs, and vectors associated with each species in different countries was documented.

RESULTS

Reports of infections related to the detection of Rickettsia species were only available for 15 out of 22 WHO-EMRO member countries. A total of twenty-four Rickettsia species, including R. sibrica, R. lusitaniae, R. africae, R. prowazekii, R. felis, R. typhi, R. rickettsii, R. aeschlimannii, R. conorii, R. massiliae, R. helvetica, R. monacensis, R. rhipicephali, R. bellii, R. asembonensis, R. hoogstraalii, R. andeanae, R. raoultii, R. asiatica, R. slovaca, R. australis, R. barbariae, Candidatus R. amblyommii, and Candidatus R. goldwasserii, were reported from WHO-EMRO member countries. Furthermore, human cases infected with six different Rickettsia species, including R. sibrica, R. prowazekii, R. felis, R. typhi, R. rickettsii, R. aeschlimannii, R. conorii, R. massiliae, and R. helvetica, were reported from these countries.

CONCLUSION

The vast diversity of Rickettsia vectors has contributed to the ongoing discovery of new Rickettsia species. Therefore, further research on the reservoir hosts of Rickettsia infections in the understudied WHO-EMRO region is crucial. This research sheds light on Rickettsia disease's epidemiology and transmission dynamics in this region.

Tick-Borne Co-Infections: Challenges in Molecular and Serologic Diagnoses

Co-infections are a poorly understood aspect of tick-borne diseases. In the United States alone, nineteen different tick-borne pathogens have been identified. The majority of these agents are transmitted by only two tick species, Ixodes scapularis and Amblyomma americanum. Surveillance studies have demonstrated the presence of multiple pathogens in individual ticks suggesting a risk of polymicrobial transmission to humans. However, relatively few studies have explored this relationship and its impact on human disease. One of the key factors for this deficiency are the intrinsic limitations associated with molecular and serologic assays employed for the diagnosis of tick-borne diseases. Limitations in the sensitivity, specificity and most importantly, the capacity for inclusion of multiple agents within a single assay represent the primary challenges for the accurate detection of polymicrobial tick-borne infections. This review will focus on outlining these limitations and discuss potential solutions for the enhanced diagnosis of tick-borne co-infections.

Diversity of rickettsiae in ticks (Acari: Ixodidae) collected from wild vertebrates in part of the Amazon, Cerrado, and Pantanal biomes in Brazil

Ticks parasitizing 102 wild animals in the states of Mato Grosso and Goiás, Brazil were collected between 2015 and 2018. A total of 2338 ticks (865 males, 541 females, 823 nymphs, and 109 larvae) belonging to four genera (Amblyomma, Dermacentor, Haemaphysalis, and Rhipicephalus) and at least 21 species were identified. DNA extraction and a molecular survey for rickettsial agents were performed on 650 ticks. The results revealed parasitism by the following species: Rickettsia amblyommatis in Amblyomma cajennense s.s., A. cajennense s.l., Amblyomma coelebs, Amblyomma humerale, Amblyomma longirostre, Amblyomma nodosum, Amblyomma scalpturatum, Amblyomma sculptum, and Amblyomma romitii; Rickettsia parkeri in Amblyomma nodosum, Amblyomma ovale, Amblyomma scalpturatum, and Amblyomma triste; Rickettsia rhipicephali in Haemaphysalis juxtakochi; Rickettsia sp. in A. cajennense s.s., A. nodosum, and A. sculptum, and lastly, 'Candidatus Rickettsia andeanae' in Amblyomma parvum and Rhipicephalus microplus. This study expands the body of knowledge about tick parasitism among wild animals, including new data concerning tick-host associations, and provides information about the epidemiology of tick-borne pathogens in the Center-West region of Brazil.

Rickettsia communities and their relationship with tick species within and around the national park of Iguaçu, Brazil

We report Rickettsia species from 2,334 ticks collected from environment (1,939 ticks) and animals (395 ticks) in the largest inland fragment of the Atlantic rainforest of southern Brazil and its fragments. Additionally, the DNA infection rates of Amblyomma ovale tick populations in the Neotropics with Rickettsia bellii and Rickettsia parkeri strain Atlantic rainforest were calculated using data from scientific publications, and their correlation was evaluated. From 11 tick species Rickettsia DNA was detected in seven (Amblyomma brasiliense, Amblyomma coelebs, Amblyomma incisum, Amblyomma longirostre, A. ovale, Haemaphysalis juxtakochi, Ixodes fuscipes) and was not detected in four species (Amblyomma dubitatum, Ixodes loricatus, Rhipicephalus microplus and Rhipicephalus sanguineus sensu lato). DNA of five Rickettsia species was detected (R. bellii, Rickettsia amblyommatis, Rickettsia rhipicephali, Rickettsia felis and Rickettsia sp. Aragaoi). To determine the prevalence of Rickettsia DNA positivity according to vector species, ticks were processed individually or in pools of 2-10 individuals (samples). The most prevalent Rickettsia species was R. bellii, found in 112 samples, followed by R. amblyommatis, R. rhipicephali, R. felis and Rickettsia sp. Aragaoi, found in 16, five, two and one sample, respectively. Rickettsia bellii DNA was found in five tick species with the highest infection rate in A. ovale and A. brasiliense. Absence of R. parkeri strain Atlantic rainforest in A. ovale ticks was an unexpected result. Furthermore, a negative correlation was identified between the infection rates (DNA) of R. bellii and/or R. parkeri strain Atlantic rainforest within A. ovale tick populations in the Neotropics. Putting together current knowledge, it can be proposed that, within natural settings, the diversity of rickettsiae and ticks creates a buffering effect on the overgrowth of rickettsiae and episodes of bacteremia in the hosts.

First isolation of Rickettsia amblyommatis from Amblyomma mixtum in Colombia

BACKGROUND

Rickettsiae are obligate intracellular Gram-negative bacteria that are the causative agent of rickettsioses and are spread to vertebrate hosts by arthropods. There are no previous reports of isolation of Rickettsia amblyommatis for Colombia.

METHODS

A convenience sampling was executed in three departments in Colombia for direct collection of adult ticks on domestic animals or over vegetation. Ticks were screened for the presence of Rickettsia spp. by real-time polymerase chain reaction (qPCR) amplifying the citrate synthase gene (gltA), and the positive sample was processed for isolation and further molecular characterization by conventional PCR. The absolute and relative frequencies were calculated for several tick species variables. All products from conventional PCR were further purified and sequenced by the Sanger technique. Representative sequences of 18 Rickettsia species were downloaded from GenBank. Consensus phylogenetic trees were constructed for the gltA, ompB, ompA, and htrA genes with 1000 replicates, calculating bootstrap values through the maximum likelihood method and the generalized time reversible substitution model in the MEGA 7.0 software program.

RESULTS

One female Amblyomma mixtum collected on vegetation was amplified by qPCR (gltA), indicating a frequency of 1.6% (1/61) for Rickettsia spp.

INFECTION

Sequence analysis of a rickettsial isolate from this tick in BLASTn showed 100% identity with gltA (340 base pairs [bp]), 99.87% for ompB (782 bp), 98.99% for htrA (497 bp), and 100% for ompA (488 bp) to R. amblyommatis. Concatenated phylogenetic analysis confirmed these findings indicating that the isolate is grouped with other sequences of Amblyomma cajennense complex from Panama and Brazil within the R. amblyommatis clade.

CONCLUSIONS

This paper describes the isolation and early molecular identification of a R. amblyommatis strain from A. mixtum in Colombia.

Rickettsia amblyommatis in Ticks: A Review of Distribution, Pathogenicity, and Diversity

Rickettsia amblyommatis is a potentially pathogenic species of Rickettsia within the spotted fever group vectored by ticks. While many studies have been published on this species, there is debate over its pathogenicity and the inhibitory role it plays in diagnosing illnesses caused by other spotted fever group Rickettsia species. Many publications have recorded the high infection prevalence of R. amblyommatis in tick populations at a global scale. While this species is rather ubiquitous, questions remain over the epidemiological importance of this possible human pathogen. With tick-borne diseases on the rise, understanding the exact role that R. amblyommatis plays as a pathogen and inhibitor of infection relative to other tick-borne pathogens will help public health efforts. The goal of this review was to compile the known literature on R. amblyommatis, review what we know about its geographic distribution, tick vectors, and pathogenicity, assess relatedness between various international strains from ticks by phylogenetic analysis and draw conclusions regarding future research needed.

Evaluating the Clinical and Immune Responses to Spotted Fever Rickettsioses in the Guinea Pig-Tick-Rickettsia System

The guinea pig was the original animal model developed for investigating spotted fever rickettsiosis (SFR). This model system has persisted on account of the guinea pig's conduciveness to tick transmission of SFR agents and ability to recapitulate SFR in humans through clinical signs that include fever, unthriftiness, and in some cases the development of an eschar. The guinea pig is the smallest animal model for SFR that allows the collection of multiple blood and skin samples antemortem for longitudinal studies. This unit provides the basic protocols necessary to establish, maintain, and utilize a guinea pig-tick-Rickettsia model for monitoring the course of infection and immune response to an infection by spotted fever group Rickettsia (SFGR) that can be studied at biosafety level 2 (BSL-2) and arthropod containment level 2 (ACL-2); adaptations must be made for BSL-3 agents. The protocols cover methods for tick feeding and colony development, laboratory infection of ticks, tick transmission of Rickettsia to guinea pigs, and monitoring of the course of infection through clinical signs, rickettsial burden, and immune response. It should be feasible to adapt these methods to study other tick-borne pathogens. © 2022 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Tick transmission of SFGR to guinea pigs Support Protocol 1: Laboratory infection of ticks by injection Alternate Protocol 1: Needle inoculation of SFGR to guinea pigs Basic Protocol 2: Monitoring the course of guinea pig rickettsial infection: clinical signs Basic Protocol 3: Monitoring the course of guinea pig rickettsial infection: collection of biological specimens Support Protocol 2: Guinea pig anesthesia Basic Protocol 4: Monitoring rickettsial burden in guinea pigs by multiplex qPCR Basic Protocol 5: Monitoring guinea pig immune response to infection: blood leukocytes by flow cytometry Basic Protocol 6: Monitoring immune response to guinea pig rickettsial infection: leukocyte infiltration of skin at the tick bite site by flow cytometry Basic Protocol 7: Monitoring the immune response to guinea pig rickettsial infection: antibody titer by ELISA Support Protocol 4: Coating ELISA Plates Alternate Protocol 2: Monitoring immune response to guinea pig rickettsial infection: antibody titer by immunofluorescence assay.

Rickettsia-Host-Tick Interactions: Knowledge Advances and Gaps

Ticks are hematophagous ectoparasites capable of transmitting multiple human pathogens. Environmental changes have supported the expansion of ticks into new geographical areas that have become the epicenters of tick-borne diseases (TBDs). The spotted fever group (SFG) of Rickettsia frequently infects ticks and causes tick-transmitted rickettsioses in areas of endemicity where ixodid ticks support host transmission during blood feeding. Ticks also serve as a reservoir for SFG Rickettsia. Among the members of SFG Rickettsia, R. rickettsii causes Rocky Mountain spotted fever (RMSF), the most lethal TBD in the United States. Cases of RMSF have been reported for over a century in association with several species of ticks in the United States. However, the isolation of R. rickettsii from ticks has decreased, and recent serological and epidemiological studies suggest that novel species of SFG Rickettsia are responsible for the increased number of cases of RMSF-like rickettsioses in the United States. Recent analyses of rickettsial genomes and advances in genetic and molecular studies of Rickettsia provided insights into the biology of Rickettsia with the identification of conserved and unique putative virulence genes involved in the rickettsial life cycle. Thus, understanding Rickettsia-host-tick interactions mediating successful disease transmission and pathogenesis for SFG rickettsiae remains an active area of research. This review summarizes recent advances in understanding how SFG Rickettsia species coopt and manipulate ticks and mammalian hosts to cause rickettsioses, with a particular emphasis on newly described or emerging SFG Rickettsia species.

Brown Dog Tick (Rhipicephalus sanguineus Sensu Lato) Infection with Endosymbiont and Human Pathogenic Rickettsia spp., in Northeastern México

Of the documented tick-borne diseases infecting humans in México, Rocky Mountain spotted fever (RMSF), caused by the Gram-negative bacterium Rickettsia rickettsii, is responsible for most fatalities. Given recent evidence of brown dog tick, Rhipicephalus sanguineus s.l., as an emerging vector of human RMSF, we aimed to evaluate dogs and their ticks for rickettsiae infections as an initial step in assessing the establishment of this pathosystem in a poorly studied region of northeastern México while evaluating the use of dogs as sentinels for transmission/human disease risk. We sampled owned dogs living in six disadvantaged neighborhoods of Reynosa, northeastern México to collect whole blood and ticks. Of 168 dogs assessed, tick infestation prevalence was 53%, composed of exclusively Rh. sanguineus s. l. (n = 2170 ticks). Using PCR and sequencing, we identified an overall rickettsiae infection prevalence of 4.1% (n = 12/292) in ticks, in which eight dogs harbored at least one infected tick. Rickettsiae infections included Rickettsia amblyommatis and Rickettsia parkeri, both of which are emerging human pathogens, as well as Candidatus Rickettsia andeanae. This is the first documentation of pathogenic Rickettsia species in Rh. sanguineus s.l. collected from dogs from northeastern México. Domestic dog infestation with Rickettsia-infected ticks indicates ongoing transmission; thus, humans are at risk for exposure, and this underscores the importance of public and veterinary health surveillance for these pathogens.

Association between Growth Rate and Pathogenicity of Spotted Fever Group Rickettsia

Rickettsia parkeri and Rickettsia amblyommatis are spotted fever group Rickettsia (SFGR) associated with Amblyomma ticks. R. parkeri is a recognized human pathogen that causes an eschar-associated febrile illness, while R. amblyommatis has not been confirmed as a causative agent of human disease. We hypothesized that the rate of replication is one of the factors contributing to rickettsial pathogenicity. In this study, growth and infectivity of R. parkeri and R. amblyommatis in mammalian (Vero E6) and tick-derived (ISE6) cell lines were assessed and compared over a 96-hour time course of infection using quantitative real-time polymerase chain reaction and microscopy. The pathogenic R. parkeri displayed a significantly higher level of infection in both Vero E6 and ISE6 cells than R. amblyommatis at 72 hours post-inoculation (hpi). Distinct growth profiles between rickettsial species with known and uncertain pathogenicity were identified. R. parkeri burdens were significantly greater than those of R. amblyommatis from 24 to 96 hpi. The relative fold changes of load were significantly higher in the pathogenic agent than in R. amblyommatis from 48 hpi onward and reached the maximum fold increase of ~2002- and ~296-fold in Vero E6 cells and ~1363- and ~161-fold in ISE6 cells, respectively, at 96 hpi. The results from the present study demonstrate that growth rate is associated with the pathogenicity of rickettsiae. Understanding SFGR growth characteristics in mammalian and tick cells will provide insight into rickettsial biology and pathogenesis.

Molecular detection of Rickettsia amblyommatis and Rickettsia parkeri in ticks collected from wild pigs in Campeche, Mexico

Tick-borne rickettsioses are caused at least by 15 species of Rickettsia of the Spotted fever group, which represent a major emerging and re-emerging public health problem worldwide. Some of these microorganisms have complex cycles involving the interaction of multiple species of ticks and wild and domestic mammals. Rickettsia infection was investigated in ticks collected from wild pigs at six localities in southeastern Mexico. We collected and tested 196 ticks belonging to four species, including Amblyomma maculatum, Amblyomma mixtum, Amblyomma ovale and Riphicephalus microplus, from 13 of 20 (65%) wild pigs sampled. Overall, Rickettsia DNA was detected in 13.8% of ticks tested (10 ♂ and 17 ♀). Of the 27 Rickettsia-positive ticks, six were A. maculatum, and 21 A. mixtum. Sequencing and phylogenetic analysis of the gltA and ompB genes revealed the presence of Rickettsia parkeri sensu stricto in one female A. maculatum and Rickettsia amblyommatis in five A. maculatum (2 ♂, 3 ♀) and 21 A. mixtum ticks (8 ♂, 13 ♀). The finding of two rickettsial agents in ticks collected from a wild pig population that is regularly captured and kept in captivity or hunted as a source of food raises concern about potential disease transmission to humans and domestic animals. However, more investigations are needed to further understand the ecology of Rickettsia species in free-ranging animals and their implications for human health.

Presence of two species of the Amblyomma cajennense complex (Acari: Ixodidae) and probable zones of sympatry in northwestern Colombia

The A. cajennense tick complex has been thought to be the main vector of Rickettsia rickettsii in Central and South America. Studies in Colombia have determined the presence of species A. patinoi and A. mixtum of the A. cajennense complex, but it is unknown which species of this complex exist in northwestern Colombia. Our aim was to identify the species of the A. cajennense complex that are present in northwestern Colombia. We sampled ticks of A. cajennense sensu lato infesting equids. Females identified according to the morphology of their genital pore were selected for genetic confirmation. Specimens from each locality were selected to perform molecular and genetic analysis. Specimens were analyzed from five departments (Antioquia, Bolívar, Córdoba, Magdalena, and Sucre). Morphologically 65 specimens were identified as A. patinoi and 5 as A. mixtum. Molecular analysis allowed to confirm the morphological identification of 27 specimens. In this study A. patinoi was widely distributed in the departments of Antioquia, Bolívar, and Córdoba with allopatric and sympatric distribution in some places. These two species in the region could have unexpected effects on the epidemiology of rickettsiosis.

Molecular detection and identification of spotted fever group rickettsiae in ticks collected from horses in Cuba

Spotted fever group (SFG) rickettsiae are obligatory intracellular bacteria that cause disease in humans and other animals. Ixodid ticks are the principal vectors of SFG rickettsiae. The present study aimed to determine the prevalence and species identity of SFG rickettsiae in ticks and horses from urban and rural areas of western Cuba using PCR assays. Tick samples, collected from 79 horses, consisted of 14 Amblyomma mixtum adults, 111 Dermacentor nitens adults and 19 pools of D. nitens nymphs (2-5 individuals/pool). The PCR results revealed the presence of Rickettsia spp. in 64% of the A. mixtum adults, 16% of the D. nitens adults, and 11% of the pooled samples of D. nitens nymphs. In contrast, Rickettsia spp. was not detected in any of the 200 horse blood samples included in this study. DNA sequence data of the rickettsial 17 kDa antigen gene showed that Rickettsia amblyommatis was present in A. mixtum; and Rickettsia felis in D. nitens. This is the first report of R. felis in D. nitens in Cuba. The present study extends our knowledge of the potential vector spectrum and distribution of SFG rickettsiae pathogens in western Cuba.

Virulence potential of Rickettsia amblyommatis for spotted fever pathogenesis in mice

Rickettsia amblyommatis belongs to the spotted fever group of Rickettsia and infects Amblyomma americanum (Lone Star ticks) for transmission to offspring and mammals. Historically, the geographic range of A. americanum was restricted to the southeastern USA. However, recent tick surveys identified the progressive northward invasion of A. americanum, contributing to the increased number of patients with febrile illnesses of unknown etiology after a tick bite in the northeastern USA. While serological evidence strongly suggests that patients are infected with R. amblyommatis, the virulence potential of R. amblyommatis is not well established. Here, we performed a bioinformatic analysis of three genome sequences of R. amblyommatis and identified the presence of multiple putative virulence genes whose products are implicated for spotted fever pathogenesis. Similar to other pathogenic spotted fever rickettsiae, R. amblyommatis replicated intracellularly within the cytoplasm of tissue culture cells. Interestingly, R. amblyommatis displayed defective attachment to microvascular endothelial cells. The attachment defect and slow growth rate of R. amblyommatis required relatively high intravenous infectious doses to produce dose-dependent morbidity and mortality in C3H mice. In summary, our results corroborate clinical evidence that R. amblyommatis can cause mild disease manifestation in some patients.

Diversity of Rickettsia in ticks collected from wild animals in Panama

This paper presents new data about Rickettsia species detected in ticks collected from wild animals, using 16S rRNA, gltA and ompA. Rickettsia DNA was found in 66 of 101 ticks. Using EZ BioCloud libraries were produced reads that identified Rickettsia aeschlimannii, and Illumina BaseSpace produced reads of Rickettsia rickettsii group, Rickettsia bellii group, and unclassified Rickettsia. Using gltA and ompA gene-specific primers, R. aeschlimannii could not be confirmed, but detection of Rickettsia amblyommatis was achieved in Amblyomma auricularium, Amblyomma geayi, Amblyomma mixtum, and Amblyomma pacae; R. bellii from Amblyomma dissimile, "Candidatus Rickettsia colombianensi" from A. dissimile, Rickettsia spp. closely related to R. raoultii from A. geayi, Rickettsia tamurae from A. dissimile, and Rickettsia endosymbionts of Ixodes from Ixodes affinis. There were no databases available specifically for 16S rRNA of Neotropical Rickettsia, highlighting the need to use species primers over only 16S rRNA primers to achieve more accurate interpretations and identifications. These findings increase the number of Rickettsia species detected in Panama and highlight the need to establish isolates to further characterize the nature of Rickettsia in the area.

Assessment of the Pathogenicity of Rickettsia amblyommatis, Rickettsia bellii, and Rickettsia montanensis in a Guinea Pig Model

Members of the genus Rickettsia range from nonpathogenic endosymbionts to virulent pathogens such as Rickettsia rickettsii, the causative agent of Rocky Mountain spotted fever. Many rickettsiae are considered nonpathogenic because they have been isolated from ticks but not vertebrate hosts. We assessed the ability of three presumed endosymbionts: Rickettsia amblyommatis, Rickettsia bellii, and Rickettsia montanensis, to infect a guinea pig animal model. These species were chosen because of their high prevalence in respective tick vectors or published reports suggestive of human or animal pathogenicity. Following intraperitoneal (IP) inoculation of cell culture suspensions of R. rickettsii, R. amblyommatis, R. bellii, or R. montanensis into guinea pigs, animals were monitored for signs of clinical illness for 13 days. Ear biopsies and blood samples were taken at 2- to 3-day intervals for detection of rickettsial DNA by PCR. Animals were necropsied and internal organ samples were also tested using PCR assays. Among the six guinea pigs inoculated with R. amblyommatis, fever, orchitis, and dermatitis were observed in one, one, and three animals respectively. In R. bellii-exposed animals, we noted fever in one of six animals, orchitis in one, and dermatitis in two. No PCR-positive tissues were present in either the R. amblyommatis- or R. bellii-exposed groups. In the R. montanensis-exposed group, two of six animals became febrile, two had orchitis, and three developed dermatitis in ears or footpads. R. montanensis DNA was detected in ear skin biopsies collected on multiple days from three animals. Also, a liver specimen from one animal and spleen specimens of two animals were PCR positive. The course and severity of disease in the three experimental groups were significantly milder than that of R. rickettsii. This study suggests that the three rickettsiae considered nonpathogenic can cause either subclinical or mild infections in guinea pigs when introduced via IP inoculation.

Mechanisms Affecting the Acquisition, Persistence and Transmission of Francisella tularensis in Ticks

Over 600,000 vector-borne disease cases were reported in the United States (U.S.) in the past 13 years, of which more than three-quarters were tick-borne diseases. Although Lyme disease accounts for the majority of tick-borne disease cases in the U.S., tularemia cases have been increasing over the past decade, with >220 cases reported yearly. However, when comparing Borrelia burgdorferi (causative agent of Lyme disease) and Francisella tularensis (causative agent of tularemia), the low infectious dose (<10 bacteria), high morbidity and mortality rates, and potential transmission of tularemia by multiple tick vectors have raised national concerns about future tularemia outbreaks. Despite these concerns, little is known about how F. tularensis is acquired by, persists in, or is transmitted by ticks. Moreover, the role of one or more tick vectors in transmitting F. tularensis to humans remains a major question. Finally, virtually no studies have examined how F. tularensis adapts to life in the tick (vs. the mammalian host), how tick endosymbionts affect F. tularensis infections, or whether other factors (e.g., tick immunity) impact the ability of F. tularensis to infect ticks. This review will assess our current understanding of each of these issues and will offer a framework for future studies, which could help us better understand tularemia and other tick-borne diseases.

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.

Detection of Amblyomma mixtum (Acari: Ixodidae) in Germany on a Human Traveler Returning From Cuba

The importation of exotic ticks to Germany on infested humans is rarely reported. Here we describe the detection of an Amblyomma mixtum nymph harboring Rickettsia amblyommatis by a tourist returning from a holiday trip to Cuba. Tick infestation may be neglected by tourists. Therefore, careful anamnesis and diagnosis should be carried out when tourists return from tropical and subtropical countries suffering from nonspecific symptoms, such as fever and malaise.

Novel PCR exclusion assay to detect spotted fever group rickettsiae in the lone star tick (Amblyomma americanum)

The lone star tick (Amblyomma americanum) is the most common and abundant human-biting tick in the southeastern United States where spotted fever rickettsioses frequently occur. However, the role of this tick in transmitting and maintaining pathogenic and non-pathogenic spotted fever group rickettsiae (SFGR) remains poorly defined. This is partially due to the high prevalence and abundance of Rickettsia amblyommatis in most populations of A. americanum. Many molecular assays commonly employed to detect rickettsiae use PCR primers that target highly conserved regions in the SFGR so low abundance rickettsia may not be detected when R. amblyommatis is present. It is costly and inefficient to test for low abundance rickettsial agents with multiple individual specific assays even when they are multiplexed, as most samples will be negative. Real time PCR assays may also be hampered by inadequate limits of detection (LODs) for low abundance agents. We exploited the absence of an otherwise relatively SFGR-conserved genome region in R. amblyommatis to design a hemi-nested PCR-assay which has a sensitivity of 10 copies in detecting the presence of most SFGR, but not R. amblyommatis in DNA of infected lone star ticks. This deletion is conserved in 21 isolates of R. amblyommatis obtained from multiple states. We demonstrated the assay's utility by detecting a pathogenic SFGR, Rickettsia parkeri, in 15/50 (30 %) of field collected A. americanum ticks that were previously screened with conventional assays and found to be positive for R. amblyommatis. These co-infected ticks included 1 questing female, 6 questing nymphs, and 8 attached males. The high prevalence of R. parkeri among host-attached ticks may be due to several variables and does not necessarily reflect the risk of disease transmission from attached ticks to vertebrate hosts. This novel assay can provide accurate estimates of the prevalence of less common SFGR in A. americanum and thus improve our understanding of the role of this tick in the maintenance and transmission of the SFGR commonly responsible for human rickettsioses.

Exposure of dogs to Rickettsia spp. in Costa Rica: Risk factors for PCR-positive ectoparasites and seropositivity

Infection of dogs with Rickettsia spp. can result in inapparent, mild, or severe disease. Moreover, common dog ticks and fleas are able to transmit rickettsiae to nearby humans. In this study, the seroprevalence of spotted fever group (SFG) rickettsiae was determined in dogs of Costa Rica, as well as possible risk factors associated with exposure. An interview of owners and clinical examinations were performed in a country-wide sample of 441 dogs. IgG antibodies were determined in 399 dogs by indirect immunofluorescence assay (IFA) using antigens of Rickettsia rickettsii, R. amblyommatis, and R. felis. The presence of Rickettsia spp. gltA gene was evaluated by PCR in ticks and fleas. Poisson regression was performed to assess possible risk factors associated with seropositivity, as well as with having PCR-positive ticks and fleas. The overall seroprevalence to SFG rickettsiae was 10.0% (end titers 64 to 256). Rhipicephalus sanguineus s.l. (116/441; 26.3%) and Ctenocephalides felis (153/441; 34.7%) were the most common ectoparasites. Rickettsia DNA was detected in 30% (39/130) and 32.3% (56/173) of tick and flea pools, respectively. Seropositivity was significantly associated with mean age of 2 to 7 years, scrotal edema, walking problems, large size, and tick and flea infestation. Being a purebred dog was a possible protective factor. The presence of Rickettsia PCR-positive ticks was associated with being a purebred dog, while flea treatment was protective. Having PCR-positive fleas was associated with being purebred and the number of people in the dog's environment; protective factors were free roaming and being an outdoor dog. Results confirm that dogs in Costa Rica are exposed to different species of SFG rickettsiae. This may represent a risk to human health and underscores the need for accurate diagnosis in dogs and humans. Surveillance of rickettsial infection in canines may provide useful indicators to understand the epidemiology of these zoonoses.

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10% of dogs were exposed to different species of SFG rickettsiae in Costa Rica.

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Risk factors included age, large size, and tick and flea infestation.

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Rickettsiae were detected in approximately 30% of flea and tick pools.

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Flea treatment and free roaming were protective against infected ticks and fleas.

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Surveillance and accurate diagnosis are required in dogs and humans.

Strain diversity of Rickettsia amblyommatis in ticks infesting birds in the North Huetar conservation area of Costa Rica

Although the presence of rickettsial agents in ticks infesting wild birds in Costa Rica has been recently reported, information on strain diversity is limited to selected rickettsial species. In order to mine deeper into rickettsial agents of ticks infesting Costa Rica wild birds a total of 399 birds from the North Huetar Conservation Area of Costa Rica were captured, and 134 immature ticks (76 larvae and 58 nymphs) were recovered from 61 birds. Ticks were tested for the presence of Rickettsia spp. by conventional PCR and sequencing of the gltA, ompA, ompB, 17 kDa, and groEL genes. Six (11.3%) Amblyomma longirostre and Amblyomma geayi ticks collected from passeriform birds, yielded amplicons of the expected size. Amplicons were sequenced, and BLAST results collectively showed that all sequences had 99-100% nucleotide identity with Rickettsia amblyommatis (formerly, 'Candidatus Rickettsia amblyommii'). Three different R. amblyommatis strains were identified. Four new tick species-host associations and the first detection of R. amblyommatis in A. geayi in Costa Rica are also reported.

Spotted Fever Group Rickettsia Infection and Transmission Dynamics in Amblyomma maculatum

Tick vectors are capable of transmitting several rickettsial species to vertebrate hosts, resulting in various levels of disease. Studies have demonstrated the transmissibility of both rickettsial pathogens and novel Rickettsia species or strains with unknown pathogenicity to vertebrate hosts during tick blood meal acquisition; however, the quantitative nature of transmission remains unknown.

Tick vectors are capable of transmitting several rickettsial species to vertebrate hosts, resulting in various levels of disease. Studies have demonstrated the transmissibility of both rickettsial pathogens and novel Rickettsia species or strains with unknown pathogenicity to vertebrate hosts during tick blood meal acquisition; however, the quantitative nature of transmission remains unknown. We tested the hypothesis that if infection severity is a function of the rickettsial load delivered during tick transmission, then a more virulent spotted fever group (SFG) Rickettsia species is transmitted at higher levels during tick feeding. Using Amblyomma maculatum cohorts infected with Rickettsia parkeri or “Candidatus Rickettsia andeanae,” a quantitative PCR (qPCR) assay was employed to quantify rickettsiae in tick salivary glands and saliva, as well as in the vertebrate hosts at the tick attachment site over the duration of tick feeding. Significantly greater numbers of R. parkeri than of “Ca. Rickettsia andeanae” rickettsiae were present in tick saliva and salivary glands and in the vertebrate hosts at the feeding site during tick feeding. Microscopy demonstrated the presence of both rickettsial species in tick salivary glands, and immunohistochemical analysis of the attachment site identified localized R. parkeri, but not “Ca. Rickettsia andeanae,” in the vertebrate host. Lesions were also distinct and more severe in vertebrate hosts exposed to R. parkeri than in those exposed to “Ca. Rickettsia andeanae.” The specific factors that contribute to the generation of a sustained rickettsial infection and subsequent disease have yet to be elucidated, but the results of this study suggest that the rickettsial load in ticks and during transmission may be an important element.

Effects of Rickettsia amblyommatis Infection on the Vector Competence of Amblyomma americanum Ticks for Rickettsia rickettsii

Although Dermacentor spp. ticks are considered the primary vectors of Rickettsia rickettsii in the United States, other North American tick species are also capable of transmitting the agent, including the lone star tick-Amblyomma americanum. The lone star tick is an aggressive human-biting tick abundant in the South, Central, and Mid-Atlantic United States, which has been shown to be a competent vector of R. rickettsii in laboratory studies. However in nature, A. americanum frequently carry Rickettsia amblyommatis-another member of the spotted fever group-with the prevalence of infection reaching 84% in some populations. It has been postulated that the presence of an endosymbiotic Rickettsia in a significant proportion of a vector population would diminish or even block transmission of pathogenic Rickettsia in ticks from generation to generation due to transovarial interference. We measured the ability of R. amblyommatis-infected A. americanum to acquire R. rickettsii from an infected host with a bloodmeal, and transmit it transstadially, horizontally (to a susceptible host), and vertically to the next generation. Larvae from both the R. amblyommatis-infected and R. amblyommatis-free cohorts acquired R. rickettsii from infected guinea pigs, but the presence of the symbiont diminished the ability of coinfected engorged larvae to transmit R. rickettsii transstadially. Conversely, acquisition of R. rickettsii by cofeeding was unaffected in R. amblyommatis-infected nymphs and adults; prevalence of R. rickettsii in engorged adults reached 97% in both R. amblyommatis-infected and R. amblyommatis-free cohorts. In guinea pigs exposed to dually infected nymphs, R. rickettsii infection was milder than in those fed upon nymphs infected with R. rickettsii only. The frequency of transovarial transmission of R. rickettsii in the R. amblyommatis-infected cohort (31%) appeared lower than that in the R. amblyommatis-free cohort (48%), but the difference was not statistically significant. Larval progenies of dually infected A. americanum females transmitted R. rickettsii to naïve guinea pigs confirming viability of the pathogen. Thus, the vector competence of A. americanum for R. rickettsii was not significantly affected by R. amblyommatis.

Detection of Rickettsia monacensis and Rickettsia amblyommatis in ticks collected from dogs in Costa Rica and Nicaragua

The neotropical climate of Central America provides ideal conditions for ticks, which may transmit several human pathogens, including spotted-fever group Rickettsia. Dogs may act as sentinels or reservoirs for human tick-borne diseases due to shared tick species. Here, ticks were collected from 680 client-owned dogs in Nicaragua and Costa Rica, and a total of 316 tick pools were investigated for Rickettsia infection by quantitative real-time PCR (qPCR) targeting the gltA gene. Subsequently, up to six further genomic targets (16S rDNA, gltA, sca4, ompA, ompB and the 23S-5S intergenic spacer) were investigated for Rickettsia species determination. The predominant tick species was Rhipicephalus sanguineus sensu lato (s.l.) (19.9% of dogs infested in Costa Rica, 48.0% in Nicaragua), followed by Ixodes boliviensis (3.1% in Costa Rica / none in Nicaragua) and Amblyomma ovale (4.8% in Costa Rica, 0.9% in Nicaragua). In total, 22 of 316 tick pools containing 60 of 1023 individual ticks were Rickettsia-positive as determined by qPCR, resulting in a minimum infection rate (MIR) of 2.2%. In detail, MIR in Rh. sanguineus s.l. was 0.7% (7/281 pools), in I. boliviensis 33.3% (12/13 pools) and in A. ovale 9.7% (3/22 pools). For 11 of 12 positive I. boliviensis pools and one of six positive Rh. sanguineus s.l. pools, the species could be determined as R. monacensis. R. amblyommatis was identified in one Rh. sanguineus s.l. pool from Costa Rica and one A. ovale pool from Nicaragua. Nine of 12 R. monacensis-positive tick pools were collected in San Rafael de Heredia, Costa Rica, indicating a high local occurrence in this area. This study supports recent evidence that R. monacensis is present on the American continent. Its high local occurrence among dog-associated I. boliviensis, which may also parasitize humans, in Costa Rica gives cause for concern, as R. monacensis is also pathogenic to humans.

A review of the genus Rickettsia in Central America

In this paper, we present a historical review of rickettsiosis in Central America and also the most recent findings of Rickettsia in ectoparasites. All countries of Central America have records of rickettsiosis. Regarding the typhus group rickettsioses, there is clinical or serological evidence of Rickettsia prowazekii in Guatemala, Rickettsia typhi in Panama, Guatemala, and Costa Rica and unidentified species of the typhus group in El Salvador. Concerning spotted fever group rickettsiosis, there is serological evidence of infection by Rickettsia akari in Costa Rica and confirmed cases involving Rickettsia rickettsii in Panama and Costa Rica. There are also reports of spotted fever group rickettsiosis in acute patients from Guatemala, Honduras, and Nicaragua. Serological studies in Central America show reactivity of Rickettsia ambyommatis, Rickettsia bellii, Rickettsia felis, Rickettsia rhipicephali, and R. rickettsii in domestic and wild mammals. Eight species of Rickettsia have been detected in ectoparasites from Central America: R. africae (or very similar), R. amblyommatis, R. asembonensis, R. bellii, R. felis, R. parkeri, R. rhipicephali, and R. rickettsii, in addition to undescribed strains such as Atlantic Rainforest, Colombianensi, IbR/CRC, Barva, Aragaoi, and Candidatus "Rickettsia nicoyana;" the latter being the only one associated with Argasidae (Ornithodoros knoxjonesi). R. amblyommatis is the most common species in Central America, seeing as it has been reported in 10 species of ticks and one of fleas in five of the seven countries of the region. In this study, we demonstrate that the genus Rickettsia is widely distributed in Central America and that rickettsiosis could be an underestimated problem in the absence of greater diagnostic efforts in undetermined febrile cases.

Rickettsia amblyommatis infecting Amblyomma pseudoconcolor in area of new focus of spotted fever in northeast Brazil

In Brazil, active infections of Rickettsia spp. is confirmed in all regions, involving various species of ticks. During investigation of a new focus of Spotted Fever (SF) incidence in the state of Pernambuco, northeastern Brazil, tick species Rhipicephalus sanguineus sensu lato (Latreille), and Amblyomma pseudoconcolor were collected from one Canis familiaris and four Euphractus sexcinctus, respectively, and analized for the presence of rickettsial genes. Ten A. pseudoconcolor ticks (90.9%) were found to be infected with Rickettsia, whereas no evidence of Rickettsia spp. was found in R. sanguineus s. l. Genetic analysis based of five rickettsial genes showed that the detected strain is most closely related to Rickettsia amblyommatis (formerly Candidatus Rickettsia amblyommii). R. amblyommatis was, for the first time, detected in Amblyomma pseudoconcolor and the results pointed to this tick like a potential vector in the enzootic cycle of R. amblyommatis in a typical semiarid Brazilian savannah region. In conclusion, despite the need for further studies to confirm if R. amblyommatis was responsible for the observed case in the state of Pernambuco, the presence of this bacterium during an SF focussed investigation should be a major concern in terms of public health due the capacity of SF for rapid and extensive dispersion within Brazilian territory.

Isolation of Rickettsia amblyommatis in HUVEC line

Rickettsia amblyommatis, formerly named Rickettsia amblyommii and ‘Candidatus Rickettsia amblyommii’ is an intracellular bacterium belonging to the spotted fever group Rickettsia. It is highly prevalent in Amblyomma americanum and in other Amblyomma spp. throughout the Western Hemisphere. R. amblyommatis has been cultivated in chicken fibroblast, primary embryonated chicken eggs, Vero cells and arthropod-derived cells. Because of the affinity of rickettsiae to invade vascular endothelial cells, we tried to isolate R. amblyommatis from a nymph of Amblyomma cajennense s.l. collected in Saltillo (Coahulia, Mexico) using human umbilical vein endothelial cells (HUVEC). One tick half was analysed by ompA PCR and was found to be positive for R. amblyommatis. The other half was selected for in vitro culture of Rickettsia spp. It was triturated in 1 mL of endothelial cell growth medium with 1% antibiotic–antimycotic solution, and the homogenate was inoculated into a HUVEC line. Culture was maintained at 33°C in endothelial cell growth medium plus 2 mM l-glutamine and 2% fetal calf serum, with 5% CO_2. The medium was changed weekly. Culture was checked by Gimenez stain for Rickettsia-like intracellular organisms. After 48 days of incubation, Rickettsia-like organisms were observed in HUVEC. PCR assays and sequencing of ompA gene in the culture suspension showed 100% identity with R. amblyommatis. This isolate was successfully established in HUVEC, and it has been deposited in the collection of the Center of Rickettsioses and Arthropod-Borne Diseases, Infectious Diseases Department, Hospital San Pedro–Center of Biomedical Research from La Rioja, Logroño, Spain. The HUVEC line is a useful tool for the isolation of R. amblyommatis.

Amblyomma sculptum: genetic diversity and rickettsias in the Brazilian Cerrado biome

Amblyomma sculptum (Ixodida: Ixodidae) Berlese, 1888 is the most important tick vector in Brazil, transmitting the bioagent of the most severe form of spotted fever (SF) in part of the Cerrado (in the states of Minas Gerais and São Paulo). In another part of the Cerrado (Central-West region of Brazil), a milder form of SF has been recorded. However, neither the rickettsia nor the vector involved have been characterized. The aim of the current study was to analyse genetic variation and the presence of rickettsia in A. sculptum in Cerrado, from silent areas and with the milder form of SF. Samples were subjected to DNA extraction, amplification and sequencing of 12S rDNA, cytochrome oxidase subunit II and D-loop mitochondrial genes (for tick population analyses), and gltA, htrA, ompA and gene D (sca4) genes for rickettsia researches. Exclusive haplotypes with low frequencies, high haplotype diversity and low nucleotide diversity, star-shaped networks and significant results in neutrality tests indicate A. sculptum population expansions in some areas. Rickettsia amblyommatis, Candidatus Rickettsia andeanae and Rickettsia felis were detected. The A. sculptum diversity is not geographically, or biome delimited, pointing to a different potential in vector capacity, possibly associated with differing tick genetic profiles.

Epidemiology of Spotted Fever Group Rickettsioses and Acute Undifferentiated Febrile Illness in Villeta, Colombia

Etiology of acute undifferentiated febrile syndrome (AUFS) is often unknown, leading to inaccurate diagnosis and treatment. Villeta town has been identified as an endemic area for spotted fever group (SFG) rickettsioses but little is known about possible amplifier hosts and other Rickettsia species different from Rickettsia rickettsii. Besides, few studies have approached other AUFS etiologies in the region. We investigated the role of dengue, leptospirosis, rickettsioses, human anaplasmosis, and Q fever as possible causes of AUFS in patients from Villeta. Sera specimens and ticks from animals as well as ticks from vegetation were studied for the presence of different Rickettsia spp. Among 104 sera from patients with AUFS, 16.4%, 24.0%, and 2.9% patients seroconverted to dengue, Leptospira, and SFG Rickettsia, respectively, with a case of probable coinfection or cross-reaction with Anaplasma phagocytophilum. None of the samples were reactive for Coxiella burnetii. Sera samples from 74 horses, 118 dogs, and 62 bovines were collected and showed 33.8%, 14.4%, and 50.0% of seroprevalence for SFG Rickettsia, respectively. A total of 1,287 ixodid ticks were collected from animals/vegetation and processed in pools for polymerase chain reaction. Among them, 1.7% was positive for Rickettsia genes, and Rickettsia amblyommii, R. rickettsii, and Rickettsia spp. were found. These results confirm the circulation of dengue, different SFG Rickettsia species and the relevance of other etiologies like leptospirosis and human anaplasmosis. Further studies must identify different epidemiological variables to establish proper surveillance and control programs.

A study of ticks and tick-borne livestock pathogens in Pakistan

BACKGROUND

As obligate blood-feeding arthropods, ticks transmit pathogens to humans and domestic animals more often than other arthropod vectors. Livestock farming plays a vital role in the rural economy of Pakistan, and tick infestation causes serious problems with it. However, research on tick species diversity and tick-borne pathogens has rarely been conducted in Pakistan. In this study, a systematic investigation of the tick species infesting livestock in different ecological regions of Pakistan was conducted to determine the microbiome and pathobiome diversity in the indigenous ticks.

METHODOLOGY/PRINCIPAL FINDINGS

A total of 3,866 tick specimens were morphologically identified as 19 different tick species representing three important hard ticks, Rhipicephalus, Haemaphysalis and Hyalomma, and two soft ticks, Ornithodorus and Argas. The bacterial diversity across these tick species was assessed by bacterial 16S rRNA gene sequencing using a 454-sequencing platform on 10 of the different tick species infesting livestock. The notable genera detected include Ralstonia, Clostridium, Staphylococcus, Rickettsia, Lactococcus, Lactobacillus, Corynebacterium, Enterobacter, and Enterococcus. A survey of Spotted fever group rickettsia from 514 samples from the 13 different tick species generated rickettsial-specific amplicons in 10% (54) of total ticks tested. Only three tick species Rhipicephalus microplus, Hyalomma anatolicum, and H. dromedarii had evidence of infection with "Candidatus Rickettsia amblyommii" a result further verified using a rompB gene-specific quantitative PCR (qPCR) assay. The Hyalomma ticks also tested positive for the piroplasm, Theileria annulata, using a qPCR assay.

CONCLUSIONS/SIGNIFICANCE

This study provides information about tick diversity in Pakistan, and pathogenic bacteria in different tick species. Our results showed evidence for Candidatus R. amblyommii infection in Rhipicephalus microplus, H. anatolicum, and H. dromedarii ticks, which also carried T. annulata.

'Candidatus Rickettsia nicoyana': A novel Rickettsia species isolated from Ornithodoros knoxjonesi in Costa Rica

Rickettsiae are intracellular bacteria commonly associated with hematophagous arthropods. Most of them have been described in hard ticks, but some have been found in soft ticks. Here we report the detection and isolation of a new Rickettsia from Ornithodoros knoxjonesi larvae collected from Balantiopteryx plicata (Emballonuridae) in Nicoya, Costa Rica. Two ticks were processed to detect Rickettsia spp. genes gltA, ompA, ompB, and htrA by PCR. Part of the macerate was also inoculated into Vero E6 and C6/36 cell lines, and cells were evaluated by Giménez stain, indirect immunofluorescence assay (IFA), and PCR. Both ticks were positive by PCR and rickettsial growth was successful in Vero E6 cells. Amplification and sequencing of near full length rrs, gltA, sca4 genes, and fragments of ompA and ompB showed that the Rickettsia sp. was different from described species. The highest homologies were with 'Candidatus Rickettsia wissemanii' and Rickettsia peacockii: 99.70% (1321/1325) with both sequences for rrs, 99.58% (1172/1177) and 99.76% (1246/1249) for gltA, 99.26% with both sequences (2948/2970 and 2957/2979) for sca4, 98.78% (485/491) and 98.39% (2069/2115) for ompA, and 98.58 (1453/1474) and 98.92% (1459/1475) for ompB; respectively. Bat blood, spleen, liver, and lung samples analyzed for Rickettsia detection were negative. Results demonstrate that the Rickettsia isolated from O. knoxjonesi is probably an undescribed species that belongs to the spotted fever group, for which 'Candidatus Rickettsia nicoyana' is proposed. Considering that B. plicata inhabits areas where contact with humans may occur and that human parasitism by Ornithodoros has been reported in the country, it will be important to continue with the characterization of this species and its pathogenic potential.

The microbiome of neotropical ticks parasitizing on passerine migratory birds

Seasonal migration of passerine birds between temperate North America and tropical Central and South America is an ecological phenomenon. Migration of birds has been associated with the introduction of ectoparasites like ticks or tick-borne pathogens across the avian migration routes. In this study, the microbial diversity was determined in the ticks and bird DNA samples using 454 pyrosequencing of bacterial 16S rRNA gene. Tick DNA samples showed the dominance of genera Lactococcus, Francisella, Raoultella, Wolbachia and Rickettsia across all the ticks, but birds DNA did not share common microbial diversity with ticks. Furthermore, "Candidatus Rickettsia amblyommii" infection in the 91 ticks collected off the songbirds was also quantified by qPCR assay. Interestingly, "Candidatus R. amblyommii" was tested positive in 24 ticks (26% infection), and infection varied from as low as three copies to thousands of copies, but bird blood samples showed no amplification. Our results provide evidence that songbirds serve as transport carrier for immature ticks, and less likely to be a reservoir for "Candidatus R. amblyommii".

Rickettsia amblyommatis sp. nov., a spotted fever group Rickettsia associated with multiple species of Amblyomma ticks in North, Central and South America

In 1973, investigators isolated a rickettsial organism, designated strain WB-8-2T, from an adult Amblyomma americanum tick collected at Land Between the Lakes National Recreation Area, TN, USA. This organism is now recognized as highly prevalent in A. americanum, as well as several other Amblyomma species found throughout the Western hemisphere. It has been suggested that cross-reactivity to WB-8-2T and similar strains contributes to the increasing number of spotted fever cases reported in the USA. In 1995, investigators provided preliminary evidence that this strain, as well as another strain from Missouri, represented a distinct taxonomic unit within the genus Rickettsia by evaluating sequences of the 16S rRNA and 17 kDa protein genes. However, the bacterium was never formally named, despite the use of the designation 'Rickettsia amblyommii' and later 'Candidatus Rickettsia amblyommii', for more than 20 years in the scientific literature. Herein, we provide additional molecular evidence to identify strain WB-8-2T as a representative strain of a unique rickettsial species and present a formal description for the species, with the proposed name modified to Rickettsia amblyommatis sp. nov. to conform to the International Code of Nomenclature of Prokaryotes. We also establish a pure culture of strain WB-8-2T and designate it as the type strain for the species. The type strain is WB-8-2T (=CRIRC RAM004T=CSURP2882T).

Detection of rickettsiae in fleas and ticks from areas of Costa Rica with history of spotted fever group rickettsioses

Outbreaks of spotted fevers have been reported in Costa Rica since the 1950s, although vectors responsible for transmission to humans have not been directly identified. In this study, species of Rickettsia were detected in ectoparasites from Costa Rica, mostly from five study sites where cases of spotted fevers have been reported. Ticks and fleas were collected using drag cloths or directly from domestic and wild animals and pooled according to species, host, and location. Pools were analyzed initially by PCR to detect a fragment of Rickettsia spp. specific gltA gene, and those positive were confirmed by detection of htrA and/or ompA gene fragments. Partial sequences of the gltA gene were obtained, as well as at least one ompA and/or ompB partial sequence of each species. Rickettsia spp. were confirmed in 119 of 497 (23.9%) pools of ticks and fleas analyzed. Rickettsia rickettsii was identified in one nymph of Amblyomma mixtum and one nymph of Amblyomma varium. Other rickettsiae present were 'Candidatus Rickettsia amblyommii' in A. mixtum, Amblyomma ovale, Dermacentor nitens, and Rhipicephalus sanguineus s. l.; Rickettsia bellii in Amblyomma sabanerae; Rickettsia felis in Ctenocephalides felis; and Rickettsia sp. similar to 'Candidatus R. asemboensis' in C. felis, Pulex simulans, A. ovale, and Rhipicephalus microplus. Results show the presence of rickettsiae in vectors that may be responsible for transmission to humans in Costa Rica, and evidence suggests exposure to rickettsial organisms in the human environment may be common. This is the first study to report R. rickettsii in A. varium and in A. mixtum in Costa Rica.

High prevalence of "Candidatus Rickettsia amblyommii" in Amblyomma ticks from a Spotted Fever Endemic Region in North Argentina

Ticks from an endemic Spotted Fever region in Argentina were analysed by PCR for Spotted Fever Group Rickettsiae. DNA of "Candidatus Rickettsia amblyommii" was found in 21.3% of Amblyomma hadanii and in 44.0% of A. neumanni. Amblyomma sculptum (formerly A. cajennense) and Haemaphysalis juxtakochi were negative for rickettsial DNA. DNA of Rickettsia rickettsii, the etiological agent of the clinical cases reported within the studied region was not detected in the analysed sample.

Amblyomma mixtum Koch, 1844 (Acari: Ixodidae): First record confirmation in Colombia using morphological and molecular analyses

Up to some years ago, the taxon Amblyomma cajennense represented a single tick species in the New World, from southern United States to northern Argentina. Recent studies, based on genetic, reproductive and morphological data reorganized this taxon into a complex of the following 6 valid species: A. cajennense sensu stricto, Amblyomma mixtum, Amblyomma sculptum, Amblyomma interandinum, Amblyomma tonelliae, and Amblyomma patinoi. According to this classification, the A. cajennense complex is currently represented in Colombia by only one species, A. patinoi. Because the Colombian land is surrounded by confirmed records of A. mixtum in Panama and Ecuador, and by A. cajennense s.s. in Venezuela and the Brazilian Amazon, it is possible that these two species could also occur in Colombia. This study aimed to determine the occurrence of ticks of the A. cajennense complex in the Orinoquía region of Colombia. A total of 246 adult ticks of the Amblyomma genus were collected in three sampled regions: 71 females and 110 males in Arauca (Arauca Department), 27 females and 20 males in Nunchía (Casanare Department), and 10 females and 8 males in Yopal (Casanare Department). Based on morphological and molecular analyses, these ticks were identified as A. mixtum. Molecular analyses consisted of DNA sequences of two molecular markers, the nuclear second internal transcribed spacer (ITS2) and the mitochondrial cytochrome c oxidase subunit I gene (COI). The presence of A. mixtum in Colombia is of medical relevance, since this species is incriminated as a vector of Rickettsia rickettsii in Central America.

Incident Tick-Borne Infections in a Cohort of North Carolina Outdoor Workers

Tick-borne diseases cause substantial morbidity throughout the United States, and North Carolina has a high incidence of spotted fever rickettsioses and ehrlichiosis, with sporadic cases of Lyme disease. The occupational risk of tick-borne infections among outdoor workers is high, particularly those working on publicly managed lands. This study identified incident tick-borne infections and examined seroconversion risk factors among a cohort of North Carolina outdoor workers. Workers from the North Carolina State Divisions of Forestry, Parks and Recreation, and Wildlife (n = 159) were followed for 2 years in a randomized controlled trial evaluating the effectiveness of long-lasting permethrin-impregnated clothing. Antibody titers against Rickettsia parkeri, Rickettsia rickettsii, "Rickettsia amblyommii," and Ehrlichia chaffeensis were measured at baseline (n = 130), after 1 year (n = 82), and after 2 years (n = 73). Titers against Borrelia burgdorferi were measured at baseline and after 2 years (n = 90). Baseline seroprevalence, defined as indirect immunofluorescence antibody titers of 1/128 or greater, was R. parkeri (24%), R. rickettsii (19%), "R. amblyommii" (12%), and E. chaffeensis (4%). Incident infection was defined as a fourfold increase in titer over a 1-year period. There were 40 total seroconversions to at least one pathogen, including R. parkeri (n = 19), "R. amblyommii" (n = 14), R. rickettsii (n = 9), and E. chaffeensis (n = 8). There were no subjects whose sera were reactive to B. burgdorferi C6 antigen. Thirty-eight of the 40 incident infections were subclinical. The overall risk of infection by any pathogen during the study period was 0.26, and the risk among the NC Division of Forest Resources workers was 1.73 times that of workers in other divisions (95% confidence interval [CI]: 1.02, 2.92). The risk of infection was lower in subjects wearing permethrin-impregnated clothing, but not significantly (risk ratio = 0.81; 95% CI: 0.47, 1.39). In summary, outdoor workers in North Carolina are at high risk of incident tick-borne infections, most of which appear to be asymptomatic.