Reliability of International Normalized Ratio Results in the CoaguChek Pro II System in a Clinical Setting.

The National Institute of Cardiology has previously used the CoaguChek® XS Plus system (Roche Diagnostics International Ltd), comparing capillary blood prothrombin time/international normalized ratio (PT/INR) results with those obtained using BCS-XP/Thromborel (Siemens). We assessed the reliability of PT/INR results using the third-generation CoaguChek Pro II system, the CoaguChek XS Plus system, and cobas® t 411 for citrated plasma analysis. Venous and capillary PT/INR were measured (N = 204). Spearman's correlation, Bland-Altman, and concordance analysis between methods were conducted. Spearman's correlation coefficients between venous/capillary INR were high for CoaguChek Pro II versus CoaguChek XS Plus (r = 0.994), CoaguChek Pro II versus cobas t 411 (r = 0.967), and CoaguChek XS Plus versus cobas t 411 (r = 0.968). Good concordance was observed among capillary methods (concordance coefficient [κ] = 0.888) and remaining relationships (P < .001 for all): cobas t 411 versus CoaguChek XS Plus (κ = 0.696) and cobas t 411 versus CoaguChek Pro II (κ = 0.684). In conclusion, good agreement was observed between CoaguChek Pro II, CoaguChek XS Plus, and cobas t 411.

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.

Rickettsioses in Colombia during the 20th century: A historical review.

Rickettsioses are vector-borne zoonotic diseases whose etiological agents are bacteria of the genera Rickettsia and Orientia. In Colombia, literature published on rickettsioses during the 20th century is limited and disperse; to date, there are no detailed publications that compile the affected regions or the involved Rickettsia species in each outbreak. Since early works of Luis Patiño-Camargo, the study of rickettsioses gained major importance with the subsequent description of significant outbreaks in some departments of the country. During the 1940s, many articles were published reporting outbreaks probably caused by Rickettsia rickettsii, Rickettsia typhi, and Rickettsia prowazekii, as well as studies on their diagnosis, vaccination, and prophylaxis. One of the most notorious works was published by Patiño-Camargo where he named the R. rickettsii rickettsiosis as "Tobia fever". However, in the subsequent decades, these entities entered a prolonged period of neglected research and surveillance, and just gained importance until the 21st century, when new fatal cases began to be reported in the country; thus, many questions remained unanswered during this overlooked period. The present work reviewed online databases, repositories, and libraries to compile literature related to rickettsioses in Colombia published during the 20th century. Gathered data show that typhus group rickettsioses (including infections by R. typhi and R. prowazekii) were broadly distributed in departments from the Andean and Caribbean regions, and that spotted fever group rickettsioses cases (including infections by R. rickettsii) were registered in other locations different from Tobia (Cundinamarca), like Atlántico, Bolivar, and Santander departments. These findings contribute to the knowledge of these diseases, their historical distribution, public health burden, and set new horizons for rickettsioses research in different Colombian locations.

Molecular detection of tick-borne rickettsial pathogens in ticks collected from domestic animals from Cauca, Colombia.

Some hard ticks' species can act as vectors of a wide variety of pathogens of human and animal importance such as Anaplasma, Ehrlichia and Rickettsia spp. In Colombia, a total of forty-six tick species have been described, and some of them have been implicated as vectors of some infectious agents. The department of Cauca is one of the thirty-two departments of Colombia. Most of its population lives in rural areas and depends on agriculture as the main economic activity, favoring exposure to ticks and tick-borne pathogens. Thus, the present study aimed to determine the tick species and tick-borne pathogens circulating in this region. From August to November 2017, ticks were collected from dogs, horses and cattle from eight rural areas of four municipalities in the department of Cauca. All collected ticks were classified according to taxonomic keys and organized in pools. DNA was extracted from all tick pools for molecular confirmation of tick species and detection of Anaplasma, Ehrlichia and Rickettsia spp. A total of 2809 ticks were collected which were grouped in 602 pools. Ticks were morphologically identified as Amblyomma cajennense sensu lato, Dermacentor nitens, Rhipicephalus microplus and Rhipicephalus sanguineus sensu lato. The molecular identity of A. cajennense s.l. was confirmed as Amblyomma patinoi. A total of 95% of the pools scored positive for members of the Anaplasmataceae family, of which, 7.8% and 7.3% were positive to Anaplasma and Ehrlichia spp., respectively, being identified as Anaplasma marginale, Ehrlichia minasensis and Ehrlichia canis; and 16.1% were positive for Rickettsia spp. with high identity for Rickettsia asembonensis, Rickettsia felis and Candidatus Rickettsia senegalensis. This is the first report describing the natural infection of ticks with rickettsial pathogens and the occurrence of A. patinoi ticks in Cauca department, Colombia.

Laboratory life cycle of Ornithodoros puertoricensis (Ixodida: Argasidae) collected in the Colombian Caribbean.

Three studies on the biology of Ornithodoros puertoricensis are available in the literature, using different hosts and incubation temperatures. In a previous study, we identified O. puertoricensis in the Colombian Caribbean. The aim of the present work was to analyze life cycle data along one generation from these specimens under laboratory conditions. Eggs of O. puertoricensis were collected in between fragments of bahareque material in a rural dwelling in the municipality of Planeta Rica (Córdoba Department, Colombia), and transported to the laboratory. All post-egg stages (i.e., larvae, nymphs, and adults) were incubated at 27 °C and 85% RH and fed on laboratory mice (Mus musculus). Sixteen engorged larvae were obtained to start a laboratory colony. Average feeding period for larvae was 4.6 days (4-5). The first nymphal instar (N1) did not require feeding and the subsequent nymphal stages (N2, N3, and N4) and adults had feeding periods ranging from 55 to 75 min. Average pre-molting period in nymphs was 15 days (10-21). Most of the N3 molted to males and all N4 molted to females. Two gonotrophic cycles were recorded: the first had a preoviposition period of 12 days (7-18) and produced 190 eggs (171-223), the second lasted 6.6 days (6-7) and produced 146 eggs (104-201). The mean life cycle duration (from parental eggs to F1 eggs) was 70.7 days (58.7-82.7) without fasting periods. The collected data agree with previous studies even with differences in hosts and maintenance conditions.

Long-term persistence of anti-Rickettsia rickettsii antibodies in capybaras, with passive transfer to offspring.

The bacterium Rickettsia rickettsii is the etiological agent of Brazilian spotted fever (BSF), and its most important vector to humans in Brazil is the tick Amblyomma sculptum. Capybaras are the main hosts of A. sculptum in many BSF-endemic areas and are considered valuable sentinels for BSF surveillance. This study aimed to assess the persistence of anti-R. rickettsii antibodies for long periods in capybaras and their passive transfer to offspring. For this purpose, three adult capybaras previously exposed to multiple infections with R. rickettsii were followed up until 3.1 years after their last exposure. During the study, one female delivered five cubs, of which three survived. Blood samples were collected monthly from adults and infants, and serum samples were titrated by indirect immunofluorescence assay (IFA) to determine endpoint titers of anti-R. rickettsii antibodies. All three adults remained seroreactive to R. rickettsii with high endpoint titers until the end of the study. All infants were seroreactive to R. rickettsii after birth and remained seroreactive for one to four months. This study showed that exposure of capybaras to R. rickettsii-infected A. sculptum ticks elicits a persistent antibody response. In addition, there was evidence of passive transfer of R. rickettsii-reactive antibodies to offspring.

Emerging Tickborne Bacteria in Cattle from Colombia.

Ehrlichia minasensis is a new pathogenic bacterial species that infects cattle, and Borrelia theileri causes bovine borreliosis. We detected E. minasensis and B. theileri DNA in cattle from southwestern Colombia by using PCR. E. minasensis and B. theileri should be considered potential etiologies of febrile syndrome in cattle from Colombia.

Experimental Rickettsia typhi Infection in Monodelphis domestica: Implications for Opossums as an Amplifying Host in the Suburban Cycle of Murine Typhus.

Murine typhus is an acute undifferentiated febrile illness caused by Rickettsia typhi. In the United States, its reemergence appears to be driven by a shift from the classic rat-rat flea cycle of transmission to one involving opossums (Didelphis virginiana) and cat fleas. Little is known of the ability of opossums to act as a reservoir and amplifying host for R. typhi. Here, we use Monodelphis domestica (the laboratory opossum) as a surrogate for D. virginiana. Opossums were inoculated via the intraperitoneal (IP) or intradermal (ID) route with 1 × 106 viable R. typhi. Blood and tissues were collected on days 6, 13, 20, and 27 or if moribund. Although one ID-infected opossum died, the remainder did not appear ill, whereas half of the IP-inoculated animals succumbed to infection. Rickettsemia was demonstrated in all animals through week 2 of infection and sporadically in weeks 3 and 4. Rickettsia typhi DNA was detected in all tissues, with most animals demonstrating the presence of bacteria into weeks 3 and 4. Histopathology and immunohistochemistry demonstrated typical findings of rickettsial infection. Akin to infection in rats, the demonstration of disseminated infection, typical inflammation, and prolonged rickettsemia with relatively few clinical effects (especially in the more natural route of ID inoculation) supports the potential of opossums to act as a competent mammalian reservoir and component of the zoonotic maintenance cycle of R. typhi. Understanding the dynamics of infection within opossums may have implications for the prevention and control of murine typhus.

Historical overview and update on relapsing fever group Borrelia in Latin America.

Relapsing fever group Borrelia (RFGB) are motile spirochetes transmitted to mammalian or avian hosts through the bite of hematophagous arthropods, such as soft ticks (Argasidae), hard ticks (Ixodidae) and the human clothing lice. RFGB can infect pets such as dogs and cats, as well as birds, cattle and humans. Borrelia recurrentis, B. anserina and B. theileri are considered to have worldwide distribution, affecting humans, domestic birds and ruminants, respectively. Borrelia spp. associated with soft ticks are transmitted mainly by Ornithodoros ticks and thrive in endemic foci in tropical and subtropical latitudes. Nowadays, human cases of soft tick-borne relapsing fever remain neglected diseases in several countries, and the impact these spirochetes have on the health of wild and domestic animals is largely understudied. Human infection with RFGB is difficult to diagnose, given the lack of distinguishing clinical features (undifferentiated febrile illness). Clinically, soft tick or louse-borne relapsing fever is often confused with other etiologies, such as malaria, typhoid or dengue. In Latin America, during the first half of the twentieth century historical documents elaborated by enlightened physicians were seminal, and resulted in the identification of RFGB and their associated vectors in countries such as Mexico, Panama, Colombia, Venezuela, Peru and Argentina. Almost 80 years later, research on relapsing fever spirochetes is emerging once again in Latin America, with molecular characterizations and isolations of novel RFGB members in Panama, Bolivia, Brazil and Chile. In this review we summarize historical aspects of RFGB in Latin America and provide an update on the current scenario regarding these pathogens in the region. To accomplish this, we conducted an exhaustive search of all the published literature for the region, including old medical theses deposited in libraries of medical academies. RFGB were once common pathogens in Latin America, and although unnoticed for many years, they are currently the focus of interest among the scientific community. A One Health perspective should be adopted to tackle the diseases caused by RFGB, since these spirochetes have never disappeared and the maladies they cause may be confused with etiologies with similar symptoms that prevail in the region.

Extension of the distribution of Amblyomma triste Koch, 1844: Morphological and molecular confirmation of Morphotype I in Colombia.

Ticks of the Amblyomma maculatum (Acari: Ixodidae) group are represented by three species: Amblyomma maculatum, Amblyomma tigrinum, and Amblyomma triste. This group is widely distributed throughout the Nearctic and Neotropical regions, from the United States of America (USA) to Argentina. They parasitize several vertebrates, including domestic mammals and humans. Nonetheless, the identification and distribution of the species within the group have been controversial but can be solved with integrative studies on their taxonomy and ecology. In Colombia, a Neotropical country from which up to 58 tick species have been reported, only Amblyomma maculatum Koch, 1844 (sensu stricto - s.s.) - morphotype II - has been molecularly confirmed. Here, specimens of the A. maculatum group from three departments of Colombia were examined by morphological and molecular analyses. The results confirmed the wide distribution of A. maculatum s.s. in Colombia. Furthermore, the presence of A. triste s.s. - morphotype I was confirmed for the first time at the molecular level, which broadens the distribution of this species in the American continent. Considering that both taxa are vectors of pathogens such as Rickettsia parkeri s.s., additional taxonomic, reproductive compatibility and niche distribution studies are needed, as well as the application of new molecular markers due to the controversial taxonomy. This will allow us to explore cryptic diversity within the recently established putative groups.

Domestic dogs as amplifying hosts of Rickettsia rickettsii for Amblyomma aureolatum ticks.

Brazilian spotted fever (BSF) is an acute infectious disease caused by the bacterium Rickettsia rickettsii, which is transmitted by different tick species. Due to deleterious effects caused on ticks, the horizontal transmission of R. rickettsii through amplifying hosts is crucial for its maintenance in tick populations among BSF-endemic areas. The tick Amblyomma aureolatum is the main vector of R. rickettsii in the São Paulo metropolitan area; nevertheless, it is not known which vertebrate could act as an amplifying host for this tick species. Herein, we evaluated the potential of domestic dogs - primary hosts for A. aureolatum adults in BSF-endemic areas - to act as amplifying hosts. For this purpose, A. aureolatum non-infected adults were allowed to feed on two groups of dogs: the control group (G1), composed of one dog not exposed to R. rickettsii; and, the infected group (G2), composed of three dogs infected with R. rickettsii via tick parasitism. All G2-dogs became ill, seroconverted to R. rickettsii, and rickettsial DNA was detected in 87% of the engorged females that fed on them. Transovarial transmission rate was estimated to be 25% and infected larvae successfully transmitted R. rickettsii to guinea-pigs, confirming transovarial transmission and vector competence. No rickettsial DNA was detected in individual samples of eggs or larvae, which precluded the estimation of filial infection rate, but implies that it was low. Our results suggest that domestic dogs act as amplifying hosts of R. rickettsii for A. aureolatum ticks in BSF-endemic areas in Brazil.

Ornithodoros puertoricensis (Ixodida: Argasidae) Associated With Domestic Fowl in Rural Dwellings From Córdoba Department, Caribbean Colombia.

Ticks of genus Ornithodoros are nidicolous parasites associated with a wide array of vertebrates. In humans, their bites cause hypersensitivity reactions and are capable to transmit pathogens of health concern. In the department of Córdoba, Caribbean region of Colombia, the first report of an Ornithodoros soft tick was made in 1980 by Betancourt, who described the collection of Ornithodoros talaje in human dwellings. Nevertheless, current the records of O. talaje made in South America have been questioned and likely correspond to misidentifications with morphologically similar species. Between October and December of 2020, we visited rural areas of four localities from three municipalities within the department of Córdoba: Cuero Curtido and Severá (municipality of Cereté), El Espanto (municipality of Planeta Rica), and Arroyo Negro (municipality of San Carlos). Search for soft ticks was performed in 46 human domiciles and peridomiciliary areas. We searched in areas frequented by domestic animals, inspecting cracks in the walls and fowl nests. Infestation by soft ticks was found in 13% (6/46) of visited houses. Overall, 215 ticks were collected (26 larvae, 144 nymphs and 45 adults) from nests of domestic birds or in the adjacent walls. Larvae, nymphs and adults were morphologically identified as Ornithodoros puertoricensis. Molecular identification of ticks was confirmed by sequencing the tick mitochondrial 16S gene of adults, pools of nymphs and larvae. Pairwise comparisons showed a 99% of identity with O. puertoricensis from Panama. This study reports for the first time O. puertoricensis associated with domestic fowl in rural dwellings in Colombia, and expands the geographical distribution of this tick species toward the Córdoba department. Importantly, local people described exposure to tick bites while sleeping in infested houses; therefore, the transmission of soft tick-borne pathogens is now of concern in the region.

Manifestations and Management of Flea-Borne Rickettsioses.

Murine typhus and flea-borne spotted fever are undifferentiated febrile illnesses caused by Rickettsia typhi and Rickettsia felis, respectively. These organisms are small obligately intracellular bacteria and are transmitted to humans by fleas. Murine typhus is endemic to coastal areas of the tropics and subtropics (especially port cities), where rats are the primary mammalian host and rat fleas (Xenopsylla cheopis) are the vector. In the United States, a cycle of transmission involving opossums and cat fleas (Ctenocephalides felis) are the presumed reservoir and vector, respectively. The incidence and distribution of murine typhus appear to be increasing in endemic areas of the US. Rickettsia felis has also been reported throughout the world and is found within the ubiquitous cat flea. Flea-borne rickettsioses manifest as an undifferentiated febrile illness. Headache, malaise, and myalgia are frequent symptoms that accompany fever. The incidence of rash is variable, so its absence should not dissuade the clinician to consider a rickettsial illness as part of the differential diagnosis. When present, the rash is usually macular or papular. Although not a feature of murine typhus, eschar has been found in 12% of those with flea-borne spotted fever. Confirmatory laboratory diagnosis is usually obtained by serology; the indirect immunofluorescence assay is the serologic test of choice. Antibodies are seldom present during the first few days of illness. Thus, the diagnosis requires acute- and convalescent-phase specimens to document seroconversion or a four-fold increase in antibody titer. Since laboratory diagnosis is usually retrospective, when a flea-borne rickettsiosis is considered, empiric treatment should be initiated. The treatment of choice for both children and adults is doxycycline, which results in a swift and effective response. The following review is aimed to summarize the key clinical, epidemiological, ecological, diagnostic, and treatment aspects of flea-borne rickettsioses.

Flea-borne Rickettsia species in fleas, Caldas department, Colombia.

INTRODUCTION: Rickettsioses are zoonotic diseases caused by pathogenic bacteria of the genus Rickettsia and transmitted to man by means of arthropod vectors such as ticks, fleas, mites and lice. Historically, Caldas Department has reported a significant number of cases of murine typhus to the Colombian national health surveillance system, and consequent studies of flea-borne rickettsiosis identified the circulation of Rickettsia typhi and Rickettsia felis in multiple municipalities. Our aim was to genotype species of Rickettsia detected in fleas collected from domestic and wild mammals in Caldas. METHODOLOGY: Flea samples were taken by convenience sampling from dogs, cats and wild mammals (rodents and marsupials) in 26 municipalities. Specimens were classified by current taxonomic keys and pooled for DNA extraction and molecular screening for Rickettsia spp. by PCR amplification of gltA, htrA and sca5 genes. Positive samples were genotyped by enzyme digestion (htrA) and sequencing. RESULTS: A total of 1388 flea samples were collected. Rickettsia DNA was amplified in 818 (gltA), 883 (htrA) and 424 (sca5) flea pools. Alignment analysis with available Rickettsia DNA sequences showed greater similarity with R. asembonensis (gltA) and with R. felis (sca5 and htrA). Restriction pattern was compatible with R. felis. R. typhi was not identified. CONCLUSION: The present study confirms the presence and high prevalence of R. asembonensis and R. felis in fleas from domestic and wild animals in different municipalities from Caldas Department.

Amblyomma nodosum Neumann, 1889 on collared anteaters (Tamandua tetradactyla) from the Andean region of Colombia.

Amblyomma nodosum is a Neotropical tick species distributed from Mexico to Argentina, with adult individuals infesting different mammal species, including anteaters (Pilosa: Myrmecophagidae). Few reports in Colombia have recorded this species in departments such as Meta, Tolima and Valle del Cauca. In this paper we describe this species using taxonomic, morphometric and molecular methods after collecting individuals parasitizing collared anteaters (Tamandua tetradactyla) in the departments of Cundinamarca and Tolima. Adult specimens were identified based on current taxonomic keys and different morphometric variables were documented in nonengorged individuals. Also, DNA was extracted for PCR amplification and sequencing of 16S rDNA, COI and ITS2 genes. Phylogenetic trees were built. One hundred and thirty-four adult ticks were collected and identified as Amblyomma nodosum, based on morphological, morphometric, molecular and phylogenetic analyses. This is the first study to report the presence of this tick species in the department of Cundinamarca, using multiple identification approaches, thus expanding its geographical records in Colombia.

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.

Author Correction: Clinical and serological evaluation of capybaras (Hydrochoerus hydrochaeris) successively exposed to an Amblyomma sculptum-derived strain of Rickettsia rickettsii.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Clinical and serological evaluation of capybaras (Hydrochoerus hydrochaeris) successively exposed to an Amblyomma sculptum-derived strain of Rickettsia rickettsii.

Brazilian spotted fever (BSF), caused by Rickettsia rickettsii, is the most lethal tick-borne disease in the western hemisphere. In Brazil, Amblyomma sculptum ticks are the main vector. Capybaras (Hydrochoerus hydrochaeris), the largest living rodents of the world (adults weighing up to 100 Kg), have been recognized as amplifying hosts of R. rickettsii for A. sculptum in BSF-endemic areas; i.e., once primarily infected, capybaras develop bacteremia for a few days, when feeding ticks acquire rickettsial infection. We conducted experimental infections of five capybaras with an A. sculptum-derived strain of R. rickettsii and performed clinical and bacteremia evaluation during primary and subsequent infections. Bacteremia was detected in all capybaras during primary infection, but not in subsequent infections. All animals seroconverted to R. rickettsii (titres range: 64-32,768), and remained seropositive throughout the study. Primary infection resulted in clinical spotted fever illness in four capybaras, of which two had a fatal outcome. Subsequent infections in seropositive capybaras resulted in no clinical signs. Capybaras developed a sustained immune response that prevented a second bacteremia. This condition may imply a high reproduction rate of capybaras in BSF-endemic areas, in order to continuously generate capybaras susceptible to bacteremia during primary infection.

Comparative survival of the engorged stages of Amblyomma dubitatum and Amblyomma sculptum in the laboratory: Implications for Brazilian spotted fever epidemiology.

Brazilian spotted fever (BSF), caused by the bacterium Rickettsia rickettsii, is transmitted to humans mainly by the tick Amblyomma sculptum in southeastern Brazil. In most BSF-endemic areas A. sculptum populations are sustained chiefly by capybaras (Hydrochoerus hydrochaeris), which are also the host of another tick species, Amblyomma dubitatum, not implicated in R. rickettsii transmission. Herein, we evaluated the effects of relative humidity (RH), temperature, and water immersion on the successful development of the engorged stages of A. dubitatum and compared them with recently published data under the same experimental conditions for A. sculptum. We showed that free-living developmental stages (engorged larvae, nymphs and females, and eggs) of A. dubitatum had higher survival rates when these stages were submerged in water for different periods of times (24-72 h). On the other hand, higher survival rates were observed for A. sculptum when ticks were incubated at lower RH values, 65 or 78 %, regardless of summer or winter mean temperatures. These results suggest that A. dubitatum is more adapted to humid habitats and seasonally flooding soils than A. sculptum, whereas this latter species should be more adapted than A. dubitatum to drier habitats. The implications of these results for the spatial distribution of A. dubitatum and A. sculptum, in relation to BSF epidemiology, are discussed.