Rickettsia parkeri in Argentina

Sigmodontinae rodents as potential reservoirs for Borrelia burgdorferi sensu lato in the Delta and Paraná Islands ecoregion, Argentina

The Borrelia burgdorferi sensu lato (s.l.) complex includes a group of spirochete bacteria that are involved in transmission cycles with vertebrates and the ticks associated with them. Rodents play an essential role in the ecoepidemiology of Borrelia, acting as reservoirs for the bacteria and hosts for ticks. To identify potential reservoir vertebrate hosts of Borrelia spirochetes in Argentina, we conducted molecular analyses on tissues obtained from a population of Sigmodontinae rodents inhabiting the Delta and Parana Islands ecoregion. We report the presence of B. burgdorferi s.l. complex genotypes infecting Akodon azarae and Oxymycterus rufus in this ecoregion. Phylogenetic analysis revealed at least three flaB haplotypes related to 'Candidatus Borrelia paulista' and Borrelia sp. strain Pampa from Brazil and to several Borrelia haplotypes from Uruguay. Additionally, we identified different alleles of the plasmid-borne gene ospC in B. burgdorferi s.l. infecting A. azarae and Ox. rufus. The ospC allele present in Borrelia from Ox. rufus was also detected in Borrelia from Oligoryzomys mattogrossae, indicating the ability of Borrelia harbouring this ospC allele to infect multiple Sigmodontinae species, whereas the ospC allele from Borrelia infecting A. azarae represents a novel variant. Further research is needed to determine host specificity of ospC alleles present in South America.

Natural infection of free-ranging capybaras (Hydrochoerus hydrochaeris) with Anaplasmataecea and Rickettsiaceae bacteria in the Iberá wetlands ecoregion, Argentina

The current work assessed the infection with Ehrlichia and Anaplasma species, and exposure to Rickettsia spp. in free-ranging capybaras in the Iberá wetlands ecoregion in Argentina. By indirect immunofluorescence assay, 37 out of 51 (73%) capybara sera were seropositive to Rickettsia spp., with 23.5% and 4% samples considered homologous to Rickettsia parkeri and Rickettsia bellii, respectively (or very closely related serotypes). Anaplasmataceae DNA was found to be highly prevalent in capybaras, with 33 out of 62 samples positive for Anaplasma sp. with Ct values of 28.64 ± 0.35 (average ± standard error), and 12 samples positive for Ehrlichia sp. with Ct values of 31.74 ± 0.87. Anaplasma sp. from capybaras was closely related to Anaplasma sp. reported to infect Amblyomma dubitatum in Iberá wetlands and to Anaplasma odocoilei, while the detected Ehrlichia sp. was closely related to "Candidatus Ehrlichia hydrochoerus" previously reported to infect capybaras in Brazil and A. dubitatum in Iberá wetlands. Structures compatible with Anaplasma morulae were observed in the cytoplasm of platelets from Anaplasma-positive capybaras. Our findings show that capybaras from the Iberá wetlands were exposed to Rickettsia species related to R. bellii and to the pathogen R. parkeri, and were infected with "Ca. Ehrlichia hydrochoerus" and a novel Anaplasma species, herein named "Candidatus Anaplasma capybara".

Detection of Rickettsia tamurae-like and other spotted fever group rickettsiae in ticks (Acari: Ixodidae) associated with wild birds in the Western Amazon, Brazil

Ticks are vectors for several pathogens, including bacteria belonging to the Rickettsia genus, such as Rickettsia rickettsii and Rickettsia parkeri, the causative agents of spotted fever. The aim of the present study was to investigate the tick species richness and rickettsial agents associated with wild birds captured in the Humaita Forest Reserve, Acre, in the Western Amazon region. Wild birds were captured with ornithological nets for visual inspection with the purpose of collecting ticks, which were identified through morphological analyses and molecular tests for several genes (12S rDNA, 16S rDNA, gltA, ompA, and sca4). A total of 607 wild birds were captured, 12% of which were parasitized by 268 ticks of the Amblyomma genus, with new host-parasite associations reported for Amblyomma calcaratum, Amblyomma geayi, Amblyomma longirostre, Amblyomma naponense, Amblyomma nodosum, and Amblyomma varium. Of the total ticks collected, 113 were tested for the presence of rickettsial DNA fragments, with 19 testing positive for R. parkeri in A. geayi, Rickettsia tamurae-like in Amblyomma sp., and Rickettsia amblyommatis in A. geayi, A. longirostre, and Amblyomma sp. We detected R. tamurae-like in Amblyomma larvae for the first time in the Western Brazilian Amazon biome, and registered spotted fever group rickettsiae, although the relevance of the detected species in a public health context should be further explored in South America, as well as new host-parasite interactions in this underexplored region.

‘Candidatus Rickettsia andeanae’ and Probable Exclusion of Rickettsia parkeri in Ticks from Dogs in a Natural Area of the Pampa Biome in Brazil

Spotted fever illness caused by the tick-borne pathogen Rickettsia parkeri has emerged in the Pampa biome in southern Brazil, where the tick Amblyomma tigrinum is implicated as the main vector. Because domestic dogs are commonly parasitized by A. tigrinum, this canid is also a suitable sentinel for R. parkeri-associated spotted fever. Herein, we investigate rickettsial infection in ticks, domestic dogs and small mammals in a natural reserve of the Pampa biome in southern Brazil. The ticks A. tigrinum, Amblyomma aureolatum and Rhipicephalus sanguineus were collected from dogs. Molecular analyses of ticks did not detect R. parkeri; however, at least 34% (21/61) of the A. tigrinum ticks were infected by the non-pathogenic agent ‘Candidatus Rickettsia andeanae’. Serological analyses revealed that only 14% and 3% of 36 dogs and 34 small mammals, respectively, were exposed to rickettsial antigens. These results indicate that the study area is not endemic for R. parkeri rickettsiosis. We tabulated 10 studies that reported rickettsial infection in A. tigrinum populations from South America. There was a strong negative correlation between the infection rates by R. parkeri and ‘Candidatus R. andeanae’ in A. tigrinum populations. We propose that high infection rates by ‘Candidatus R. andeanae’ might promote the exclusion of R. parkeri from A. tigrinum populations. The mechanisms for such exclusion are yet to be elucidated.

Rickettsia spp., Ehrlichia sp. and Candidatus Midichloria sp. associated to ticks from a protected urban area in Buenos Aires City (Argentina)

The aim of this study was to determine the infection with Rickettsiales in ticks and birds from the main protected urban area of Buenos Aires City (Argentina). One Amblyomma aureolatum (0.2%) and one Ixodes auritulus (0.1%) were positive by PCR targeting Rickettsia 23S-5S rRNA intergenic spacer. Phylogenetic analysis shows to findings in A. aureolatum are closely to Rickettsia bellii and for I. auritulus are related to 'Candidatus Rickettsia mendelii'. One I. auritulus (0.1%) and three A. aureolatum (0.6%) were positive by PCR for a fragment of the 16S rRNA gene of the Anaplasmataceae family. The sequences obtained from A. aureolatum were phylogenetically related to Midichloriaceae endosymbionts. The sequence from I. auritulus s.l. had 100% identity with Ehrlichia sp. Magellanica from Chile and two genotypes of Ehrlichia sp. from Uruguay. The results of our study show that Rickettsia and Ehrlichia are present in ticks in the main protected urban area of Buenos Aires City.

Phylogenetic Differentiation of Rickettsia parkeri Reveals Broad Dispersal and Distinct Clustering within North American Strains

The tick-borne pathogen Rickettsia parkeri causes a mild rickettsiosis, with cases reported from several countries to its known distribution in the Americas. Molecular analyses have identified a clear distinction between strains of R. parkeri sensu stricto (s. s.) and R. parkeri sensu lato (s. l.) as well as separation between North American and South American R. parkeri s. s. strains. To expand on this previous work, we developed a multilocus sequence typing analysis with two aims: first, to investigate the genetic diversity within strains of North American R. parkeri s. s., and second, to further the understanding of the genetic relationships between R. parkeri s. s. and R. parkeri s. l. Sixty-four R. parkeri isolates and 12 R. parkeri-positive tick lysates were analyzed using a novel typing scheme consisting of four coding regions and two intergenic regions. A concatenated Bayesian phylogeny that identified eight clades was constructed: three represent the R. parkeri s. l. strains, and five represent the R. parkeri s. s. strains. The clades appear to be generally phylogeographically organized and associated with specific tick vectors. However, while one of the four R. parkeri s. s. North American clades appears to be limited to the southwestern United States, the other North American clades exhibit broad dispersal, most notably seen in the largest group, which includes representative samples extending from northern Mexico to Delaware. This work highlights the increasingly recognized geographic range of R. parkeri in the Americas and suggests a potential public health risk for these areas.

IMPORTANCE Since 1937, when Rickettsia parkeri was originally identified in Amblyomma maculatum group ticks, the recognized range and associated vectors for this pathogen have expanded significantly. In recent years, R. parkeri has been identified in 12 tick species from seven countries in the Americas. Herein, we provide evidence that the greatest genetic diversity within R. parkeri exists in North America, where one R. parkeri sensu lato and four R. parkeri sensu stricto genotypes are present. While one distinct R. parkeri sensu stricto genotype exists only in the southwestern United States, three genotypes are broadly distributed in the eastern United States, with the largest of these found across the known range of R. parkeri in North America. In contrast, the South American R. parkeri sensu stricto samples represent a single genotype and are completely clonal at the loci analyzed, irrespective of their country of origin.

Ticks (Acari: Ixodidae) on marsh deer (Blastocerus dichotomus) at a conservation center: infestation and Rickettsia parkeri infection dynamics along nine years

The objective of this work was to evaluate the relationship between the populations of the ticks Amblyomma triste Koch, 1844, Rhipicephalus microplus (Canestrini, 1888), Amblyomma sculptum Berlese, 1888, the pathogenic bacteria Rickettsia parkeri and a marsh deer (Blastocerus dichotomus) population after its removal from a pristine environment. For this purpose, ticks were collected from the cervical region of deer at the Marsh Deer Conservation Center in Promissão, São Paulo State, Brazil for nine consecutive years (2000 - 2008). Deer in captivity at the Center were kept in 2,000 m² paddocks surrounded by two-meter-high fences in the Tiete-river marsh. In total, 1,012 ticks of 26 deer were collected. Prevalence of the species A. triste among tick-infested hosts was the highest in the first triennium but decreased to the second and further to the third triennium. In contrast, the R. microplus prevalence amidst infested host population, increased from the first to the third triennium and was the species that attained the highest infestation intensity. Amblyomma sculptum was the tick with the lowest infestation prevalence and intensity throughout the period. The change in the proportion between the two most prevalent species was attributed to the new environment, specifically its restricted size and within it a dry area more suitable for R. microplus. DNA of 424 ticks processed in 276 pools was tested for Rickettsia genetic material by polymerase chain reactions (PCR). Twenty samples of the study were positive for the rickettsial gltA gene. Of these, 18 were from A. triste ticks and revealed the presence of the ompA spotted fever group gene as well. Eleven samples were sequenced and showed 100% identity with R. parkeri sensu stricto. Two samples from R. microplus did not amplify ompA gene neither yielded product in a PCR specific for Rickettsia bellii. Sequencing of the gltA gene in the DNA of these two ticks was also 100% identical with R. parkeri s.s. In conclusion, the changes in the deer environment modified the tick populations but maintained, at least temporary, R. parkeri bacteria in A. triste ticks. Rhipicephalus microplus was refractory to the R. parkeri infection and bacterial DNA in this tick species indicated DNA spill over from other tick species. It was demonstrated that captive marsh deer may sustain cattle tick populations on its own. This would hardly occur under pristine conditions because of the inadequacy the marsh deer´s naturally humid habitat for the cattle tick. However, deer transportations of R. microplus ticks from one farm to another may occur whenever habitat loss pushes this wild animal towards farms.

Tick fauna in non-anthropogenic areas in Mato Grosso do Sul, Brazil, with the presence of the Rickettsia parkeri strain Atlantic rainforest in Amblyomma ovale

The aim of this study was to evaluate tick fauna and identify the possible presence of Rickettsia spp. in ticks of the genus Amblyomma from two environmental preservation areas in different regions of Mato Grosso do Sul state, Brazil. CO₂ traps, visual observation and cloth dragging were used to capture ticks. Three hundred ticks were submitted to the hemolymph test, and samples that showed organisms morphologically compatible with Rickettsia were used for rickettsial DNA detection by PCR. DNA was extracted using guanidine-phenol isothiocyanate, and the primers CS78 and CS323 were used for PCR, which amplified a 401-base pair fragment of the citrate synthase (gltA) gene. If positive, the DNA sample was tested by primers Rr190.70p and Rr190.602n that produce a 530 bp amplicon of the ompA gene that is present only in rickettsiae of the spotted fever group. A total of 1,745 adult ticks were collected, including 1,673 specimens of Amblyomma sculptum, 63 of Amblyomma coelebs, five of Amblyomma naponense and four of Amblyomma ovale. Thirteen ticks of the species A. ovale, A. coelebs and A. sculptum showed structures compatible with Rickettsia inside the hemocytes; after DNA extraction, the presence of Rickettsia spp. in a sample of A. ovale was confirmed by PCR in both analyzed fragments. In the sequencing analysis, 100% identity for the Rickettsia parkeri strain Atlantic rainforest was obtained according to GenBank. The two environmental preservation areas showed A. sculptum as the predominant species, as well as the presence of marked seasonality for this species. This paper is the first report of the R. parkeri strain Atlantic rainforest in A. ovale ticks in the state of Mato Grosso do Sul, Brazil.

Clinical, epidemiological, and laboratory features of Rickettsia parkeri rickettsiosis: A systematic review

Rickettsia parkeri rickettsiosis is recognized as the second most prevalent tick-borne disease caused by spotted fever group rickettsiae in the Americas, where two pathogenic strains (R. parkeri sensu stricto and R. parkeri strain Atlantic rainforest) have been related to human infections and transmitted by Amblyomma spp. ticks. We developed a systematic review that evaluated all available evidence in the literature regarding clinical, epidemiological, and laboratory features of R. parkeri rickettsiosis, including confirmed and probable cases. We followed the recommendations made by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guide. We excluded papers that contained missing information of some variables and publications in which it was not possible to separate data for confirmed and probable cases. A total of 77 clinical cases (32 confirmed cases and 45 probable cases) were considered for this review. Overall, our results show that R. parkeri rickettsiosis is more frequent in males in the age group of 18-64 years and that a history of tick exposure was frequent (>90%). Cases were described in the United States, Argentina, Brazil, Uruguay and Colombia. Clinically, more than 60% of the cases had fever (mean of 93%), eschar (mean of 87%), and rash (mean of 68%). Headache and myalgia were predominant nonspecific symptoms (mean of 67% and 61%, respectively). Our results show that at least 60% of R. parkeri cases had altered laboratory parameters, most often showing an increase in transaminases and leukopenia. Tetracyclines-class antibiotics were used in most (>85%) of the patients. Overall, only 9% of cases required hospitalization and there was a 100% rate of clinical recovery in all of cases.

Recent advances in understanding tick and rickettsiae interactions

Ticks are haematophagous arthropods with unique molecular mechanisms for digesting host blood meal while acting as vectors for various pathogens of public health significance. The tick's pharmacologically active saliva plays a fundamental role in modulating the host's immune system for several days to weeks, depending on the tick species. The vector tick has also developed sophisticated molecular mechanisms to serve as a competent vector for pathogens, including the spotted fever group (SFG) rickettsiae. Evidence is still inadequate concerning tick-rickettsiae-host interactions and saliva-assisted transmission of the pathogen to the mammalian host. Rickettsia parkeri, of the SFG rickettsia, can cause a milder version of Rocky Mountain spotted fever known as American Boutonneuse fever. The Gulf Coast tick (Amblyomma maculatum) often transmits this pathogenic rickettsia in the USA. This review discusses the knowledge gap concerning tick-rickettsiae-host interactions by highlighting the SFG rickettsia and the Am maculatum model system. Filling this knowledge gap will provide a better understanding of the tick-rickettsiae-host interactions in disease causation, which will be crucial for developing effective methods for preventing tick-borne diseases.

Housing Conditions Linked to Tick (Ixodida: Ixodidae) Infestation in Rural Areas of Colombia: A Potential Risk for Rickettsial Transmission

This cross-sectional study explores the different conditions related to the infestation of ticks in households and the potential risks for rickettsial transmission in Urabá, Colombia. The main outcome of interest was villagers' perception of tick infestation. The data were analyzed using a clog-log mixed regression model. Ticks were collected from infested humans to diagnose infection by spotted fever group rickettsiae (SFGR). In addition, a thematic analysis of qualitative data from key informants concerning knowledge about ticks was conducted. The prevalence of infestation of ticks in households was estimated at 60.99% (95% CI: 51.58-93.51). The multivariate model suggested that households with palm leaf roofs (PR = 1.95; 95% CI: 1.19-2.95), canines (PR = 1.76; 95% CI: 1.21-2.46), rats (PR = 2.19; 95% CI: 1.45-3.08), and with the presence of opossums in areas surrounding the households (PR = 1.51; 95% CI: 1.05-2.10) had a higher prevalence of tick infestation. Two samples of the tick species Amblyomma patinoi were found infected with Rickettsia amblyommatis and Candidatus Rickettsia colombianensi. A thematic analysis provided the names that local community members give to ticks, areas where ticks are common, and the individuals at risk of infestation. The presence of domestic, synanthropic, and wild animals suggests a high risk of the dissemination of ticks inside dwellings and close to them in these rural areas.

Reproductive incompatibility between Amblyomma maculatum (Acari: Ixodidae) group ticks from two disjunct geographical regions within the USA

The Amblyomma maculatum Koch group of ixodid ticks consists of three species: A. maculatum, A. triste, and A. tigrinum. However, since Koch described this group in 1844, the systematics of its members has been the subject of ongoing debate. This is especially true of A. maculatum and A. triste; recent molecular analyses reveal insufficient genetic divergence to separate these as distinct species. Further confounding this issue is the discovery in 2014 of A. maculatum group ticks in southern Arizona (AZ), USA, that share morphological characteristics with both A. triste and A. maculatum. To biologically evaluate the identity of A. maculatum group ticks from southern Arizona, we analyzed the reproductive compatibility between specimens of A. maculatum group ticks collected from Georgia (GA), USA, and southern Arizona. Female ticks from both Arizona and Georgia were mated with males from both the Georgia and Arizona Amblyomma populations, creating two homologous and two heterologous F1 cohorts of ticks: GA ♀/GA ♂, AZ ♀/AZ ♂, GA ♀/AZ ♂, and AZ ♀/GA ♂. Each cohort was maintained separately into the F2 generation with F1 females mating only with F1 males from their same cohort. Survival and fecundity parameters were measured for all developmental stages. The observed survival parameters for heterologous cohorts were comparable to those of the homologous cohorts through the F1 generation. However, the F1 heterologous females produced F2 egg clutches that did not hatch, thus indicating that the Arizona and Georgia populations of A. maculatum group ticks tested here represent different biological species.

Molecular detection of rickettsial bacteria in ticks of the genus Ixodes from the Southern Cone of America

To obtain information about rickettsial bacteria in ticks of the genus Ixodes from Argentina and Uruguay, specimens of I. fuscipes (previously named as I. aragaoi), Ixodes pararicinus, Ixodes sp. cf. I. affinis, and Ixodes sp. were tested targeting the rickettsial gltA and ompA genes. Rickettsial bacteria was detected in all of these species. Rickettsia found in Ixodes sp. is closely related to Ca. Rickettsia mendelii, which was previously detected in I. ricinus of the Czech Republic and later in I. brunneus from the USA. Phylogenetic analyses of the Rickettsia strains found in I. fuscipes, I. pararicinus, and Ixodes sp. cf. I. affinis showed that these strains form a clade together with R. buchneri detected in I. scapularis from the USA, which is closely related to R. monacensis from Europe. Rickettsia buchneri, R. cooleyi and the Rickettsia detected in I. fuscipes, I. pararicinus, and Ixodes sp. cf. I. affinis clustered together in a clade well supported, which suggest that they are different strains of R. buchneri. The phylogenetic analysis shows that Ixodes ticks that are closely related in evolutionary terms (i.e. Ixodes species from the I. ricinus complex, I. brunneus-Ixodes sp.) share closely related rickettsial strains. The results of this study show that rickettsial bacteria are present in Ixodes ticks from Argentina and describe the first detection of Ca. R. mendelii in South America.

Multi-locus phylogenetic analysis groups the New World bacterium Rickettsia sp. strain ApPR with the Old World species R. africae; proposal of "Candidatus Rickettsia paranaensis"

Rickettsia parkeri sensu stricto (s.s.) is an emerging human pathogen in the Americas. Comprehension of the etiology of R. parkeri infections in South America is complicated by the existence of genetic variants (Atlantic rainforest, NOD and Parvitarsum) of this species that are associated with specific groups of Amblyomma ticks. The rickettsial bacterium strain ApPR was first reported in Amblyomma parkeri ticks in Southern Brazil in 2012 and was considered, based on sequencing of fragments of the gltA, htrA, ompA and ompB genes, to represent yet another genetic variant of R. parkeri. In the current work, a multi-locus phylogenetic analysis employing additional genes and intragenic regions was performed using DNA extracted from (a) larvae of A. parkeri and Amblyomma species haplotype Nazaré ticks collected from wild birds, (b) a nymph of Amblyomma sp. haplotype Nazaré recovered from a monkey (Callicebus nigrifons), representing the first report of that tick parasitizing a non-human primate and (c) from a cultured isolate of ApPR, isolated from colony-reared adults of Amblyomma geayi. Phylogenetic inference performed using Maximum-likelihood (ML), Maximum Parsimony (MP) and Bayesian (B) methods, consistently placed strain ApPR outside the New World R. parkeri complex and instead grouped it in proximity to the Old World species Rickettsia africae and Rickettsia sibirica. Estimates of evolutionary divergence provided additional support for the inferred phylogenetic relationship. Given the clear evolutionary distance between strain ApPR and R. parkeri we propose the recognition of "Candidatus Rickettsia paranaensis".

[Spotted fever in Argentina. Description of two clinical cases]

Rickettsioses are zoonotic tick-borne diseases. In Argentina, there are two epidemiological scenarios: jungle of Salta and Jujuy, involving vectors from the "Amblyomma cajennense Complex" (A. sculptum, and A. toneliae) and Rickettsia rickettsii as the main etiological agent; and the second scene to Delta del Rio Paraná and Samborombón Bay, where Amblyomma triste acts as a vector; and the provinces of Córdoba, La Rioja, San Luis and La Pampa where Amblyomma tigrinum is the vector. In this second scenario, Rickettsia parkeri is the causal agent. The spotted fever (SF) due to R. rickettsii is responsible for a severe cutaneous and systemic disease. Contrarily, R. parkeri produces benign and self-limited clinical manifestation. Here we describe a fatal SF case by R. rickettsii, in El Tunal, Salta and the first SF case due to R. parkeri in San Juan.

A review on the occurrence of companion vector-borne diseases in pet animals in Latin America

Companion vector-borne diseases (CVBDs) are an important threat for pet life, but may also have an impact on human health, due to their often zoonotic character. The importance and awareness of CVBDs continuously increased during the last years. However, information on their occurrence is often limited in several parts of the world, which are often especially affected. Latin America (LATAM), a region with large biodiversity, is one of these regions, where information on CVBDs for pet owners, veterinarians, medical doctors and health workers is often obsolete, limited or non-existent. In the present review, a comprehensive literature search for CVBDs in companion animals (dogs and cats) was performed for several countries in Central America (Belize, Caribbean Islands, Costa Rica, Cuba, Dominican Republic, El Salvador, Guatemala, Honduras, Mexico, Nicaragua, Panama, Puerto Rico) as well as in South America (Argentina, Bolivia, Brazil, Chile, Colombia, Ecuador, French Guiana, Guyana (British Guyana), Paraguay, Peru, Suriname, Uruguay, Venezuela) regarding the occurrence of the following parasitic and bacterial diseases: babesiosis, heartworm disease, subcutaneous dirofilariosis, hepatozoonosis, leishmaniosis, trypanosomosis, anaplasmosis, bartonellosis, borreliosis, ehrlichiosis, mycoplasmosis and rickettsiosis. An overview on the specific diseases, followed by a short summary on their occurrence per country is given. Additionally, a tabular listing on positive or non-reported occurrence is presented. None of the countries is completely free from CVBDs. The data presented in the review confirm a wide distribution of the CVBDs in focus in LATAM. This wide occurrence and the fact that most of the CVBDs can have a quite severe clinical outcome and their diagnostic as well as therapeutic options in the region are often difficult to access and to afford, demands a strong call for the prevention of pathogen transmission by the use of ectoparasiticidal and anti-feeding products as well as by performing behavioural changes.

The Amblyomma maculatum Koch, 1844 (Acari: Ixodidae) group of ticks: phenotypic plasticity or incipient speciation?

BACKGROUND

The goal of this study was to reassess the taxonomic status of A. maculatum, A. triste and A. tigrinum by phylogenetic analysis of five molecular markers [four mitochondrial: 12S rDNA, 16S rDNA, the control region (DL) and cytochrome c oxidase 1 (cox1), and one nuclear: ribosomal intergenic transcribed spacer 2 (ITS2)]. In addition, the phenotypic diversity of adult ticks identified as A. maculatum and A. triste from geographically distinct populations was thoroughly re-examined.

RESULTS

Microscopic examination identified four putative morphotypes distinguishable by disjunct geographical ranges, but very scant fixed characters. Analysis of the separated mitochondrial datasets mostly resulted in conflicting tree topologies. Nuclear gene sequences were almost identical throughout the geographical ranges of the two species, suggesting a very recent, almost explosive radiation of the terminal operational taxonomic units. Analysis of concatenated molecular datasets was more informative and indicated that, although genetically very close to the A. maculatum - A. triste lineage, A. tigrinum was a monophyletic separate entity. Within the A. maculatum - A. triste cluster, three main clades were supported. The two morphotypes, corresponding to the western North American and eastern North American populations, consistently grouped in a single monophyletic clade with many shared mitochondrial sequences among ticks of the two areas. Ticks from the two remaining morphotypes, south-eastern South America and Peruvian, corresponded to two distinct clades.

CONCLUSIONS

Given the paucity of morphological characters, the minimal genetic distance separating morphotypes, and more importantly the fact that two morphotypes are genetically indistinguishable, our data suggest that A. maculatum and A. triste should be synonymized and that morphological differences merely reflect very recent local adaptation to distinct environments in taxa that might be undergoing the first steps of speciation but have yet to complete lineage sorting. Nonetheless, future investigations using more sensitive nuclear markers and/or crossbreeding experiments might reveal the occurrence of very rapid speciation events in this group of taxa. Tentative node dating revealed that the A. tigrinum and A. maculatum - A. triste clades split about 2 Mya, while the A. maculatum - A.triste cluster radiated no earlier than 700,000 years ago.

Vector Tick Transmission Model of Spotted Fever Rickettsiosis

Many aspects of rickettsial infections have been characterized, including pathogenic and immune pathways and mechanisms of rickettsial survival within the vertebrate host and tick vector. However, very few studies are focused on the complex pathogen-vector-host interactions during tick feeding. Therefore, our objective was to develop a tick transmission model of the spotted fever group of rickettsial infections to study the initial events in disease development. The most appropriate strain of mouse was identified for evaluation as a transmission model, and the course of infection, bacterial levels, histopathologic changes, and antibody response during tick transmission in mice infested with Amblyomma maculatum ticks carrying the emerging pathogen, Rickettia parkeri, were studied. Results showed distinct clinical signs in C3H/HeN mice infected intravenously, leading to selection of this mouse strain for tick transmission studies. Active infection of animals was observed after tick vector transmission. The bacteria disseminated systemically and spread to several organs at 24 hours after tick attachment, with peak bacterial load at day 6 after tick attachment. Skin, lung, and liver showed the greatest pathologic changes, with inflammatory cellular infiltration and necrosis. These findings indicate the feasibility of using murine infection with R. parkeri by A. maculatum tick transmission as a model to study different aspects of the spotted fever group of rickettsial disease establishment.

Detection of Ehrlichia sp. strain San Luis and Candidatus Rickettsia andeanae in Amblyomma parvum ticks

Owing to the sanitary importance of the tick Amblyomma parvum, this study evaluated the infection by Ehrlichia, Anaplasma and Rickettsia species of questing A. parvum collected in northwestern Argentina. Our results showed that A. parvum ticks in this region are infected with the recently reported Ehrlichia sp. strain San Luis, closely related to Ehrlichia chaffeensis. A high prevalence of Candidatus Rickettsia andeanae was observed. Most of the infected ticks presented rickettsial loads lower than those previously reported for other spotted fever group rickettsiae. The presence of Ehrlichia sp. strain San Luis in A. parvum is a potential risk for public health as the principal hosts of this tick are domestic mammals in rural areas and humans are frequently bitten by this tick species.

Molecular survey of Rickettsia spp. in the Neotropical deer tick Haemaphysalis juxtakochi from Brazilian Pampa

Spotted fever (SF) is a tick-borne disease associated with Rickettsia spp.. In the Pampa biome, Southern Brazil, cases of SF seem to be strongly linked with the practice of hunting wild animals. An investigation of rickettsiae in tick species found on wild animals could provide more information regarding the rickettsiosis enzootic cycle. The aim of this study is to describe the results of a molecular survey of Rickettsia spp. in the Neotropical deer tick, Haemaphysalis juxtakochi Cooley, 1946 (Acari: Ixodidae), from the Brazilian Pampa. Ticks were obtained from 14 road-killed gray brocket deer, Mazama gouazoubira (Artiodactyla: Cervidae), found in nine different municipalities of Rio Grande do Sul state, Southern Brazil. Ticks were processed individually to obtain genomic DNA, and then Rickettsia spp. was investigated using a set of PCR reactions that amplified the rickettsial fragments of the gltA, ompA, and htrA genes. Of the 24 tick samples tested, DNA of Rickettsia parkeri sensu stricto (s.s.) was found in 11 H. juxtakochi specimens collected in two different areas of the Brazilian Pampa. This is the first report of R. parkeri s.s. (the main agent associated with SF in the Uruguayan, Argentinian, and Brazilian Pampa) in H. juxtakochi ticks. These findings indicate that R. parkeri s.s. may be much more common and widely distributed in the Pampa biome than previously assumed. Moreover, H. juxtakochi ticks and gray brocket deer could participate in the potential spillover of R. parkeri s.s. from endemic to non-endemic areas in the South American Pampa.

Phylogenetic Evidence for the Existence of Multiple Strains of Rickettsia parkeri in the New World

The bacterium Rickettsia parkeri has been reported to infect ticks of the "Amblyomma maculatum species complex" in the New World, where it causes spotted fever illness in humans. In South America, three additional rickettsial strains, namely, Atlantic rainforest, NOD, and Parvitarsum, have been isolated from the ticks Amblyomma ovale, Amblyomma nodosum, and Amblyomma parvitarsum, respectively. These three strains are phylogenetically closely related to R. parkeri, Rickettsia africae, and Rickettsia sibirica Herein, we performed a robust phylogenetic analysis encompassing 5 genes (gltA, ompA, virB4, dnaA, and dnaK) and 3 intergenic spacers (mppE-pur, rrl-rrf-ITS, and rpmE-tRNA^fMet) from 41 rickettsial isolates, including different isolates of R. parkeri, R. africae, R. sibirica, Rickettsia conorii, and strains Atlantic rainforest, NOD, and Parvitarsum. In our phylogenetic analyses, all New World isolates grouped in a major clade distinct from the Old World Rickettsia species (R. conorii, R. sibirica, and R. africae). This New World clade was subdivided into the following 4 clades: the R. parkerisensu stricto clade, comprising the type strain Maculatum 20 and all other isolates of R. parkeri from North and South America, associated with ticks of the A. maculatum species complex; the strain NOD clade, comprising two South American isolates from A. nodosum ticks; the Parvitarsum clade, comprising two South American isolates from A. parvitarsum ticks; and the strain Atlantic rainforest clade, comprising six South American isolates from the A. ovale species complex (A. ovale or Amblyomma aureolatum). Under such evidences, we propose that strains Atlantic rainforest, NOD, and Parvitarsum are South American strains of R. parkeriIMPORTANCE Since the description of Rickettsia parkeri infecting ticks of the "Amblyomma maculatum species complex" and humans in the New World, three novel phylogenetic close-related rickettsial isolates were reported in South America. Herein, we provide genetic evidence that these novel isolates, namely, strains Atlantic rainforest, NOD, and Parvitarsum, are South American strains of R. parkeri. Interestingly, each of these R. parkeri strains seems to be primarily associated with a tick species group, namely, R. parkerisensu stricto with the "Amblyomma maculatum species group," R. parkeri strain NOD with Amblyomma nodosum, R. parkeri strain Parvitarsum with Amblyomma parvitarsum, and R. parkeri strain Atlantic rainforest with the "Amblyomma ovale species group." Such rickettsial strain-tick species specificity suggests a coevolution of each tick-strain association. Finally, because R. parkerisensu stricto and R. parkeri strain Atlantic rainforest are human pathogens, the potential of R. parkeri strains NOD and Parvitarsum to be human pathogens cannot be discarded.

Rickettsia parkeri (Rickettsiales: Rickettsiaceae) Detected in Ticks of the Amblyomma maculatum (Acari: Ixodidae) Group Collected from Multiple Locations in Southern Arizona

Rickettsia parkeri is an emerging human pathogen transmitted by Amblyomma ticks in predominately tropical and subtropical regions of the western hemisphere. In 2014 and 2015, one confirmed case and one probable case of R. parkeri rickettsiosis were reported from the Pajarita Wilderness Area, a semi-arid mountainous region in southern Arizona. To examine more closely the potential public health risk of R. parkeri in this region, a study was initiated to investigate the pervasiveness of Amblyomma maculatum Koch group ticks in mountainous areas of southern Arizona and to ascertain the infection frequencies of R. parkeri in these ticks. During July 2016, a total of 182 adult ticks were collected and evaluated from the Pajarita Wilderness Area in Santa Cruz County and two additional sites in Cochise and Santa Cruz counties in southern Arizona. DNA of R. parkeri was detected in a total of 44 (24%) of these ticks. DNA of "Candidatus Rickettsia andeanae" and Rickettsia rhipicephali was detected in three (2%) and one (0.5%) of the samples, respectively. These observations corroborate previous collection records and indicate that established populations of A. maculatum group ticks exist in multiple foci in southern Arizona. The high frequency of R. parkeri in these tick populations suggests a public health risk as well as the need to increase education of R. parkeri rickettsiosis for those residing, working in, or visiting this area.

Comparative analysis of germ cells and DNA of the genus Amblyomma: adding new data on Amblyomma maculatum and Amblyomma ovale species (Acari: Ixodidae)

Among tick species, members of the subfamily Amblyomminae have received special attention, since they serve as vectors for pathogens such as Rickettsia spp. and display cryptic species complexes that make their taxonomical classification challenging. Amblyomma ovale, Amblyomma maculatum, and other species of the genus Amblyomma have shown a long history of taxonomic controversies. Spermiotaxonomy has proved to be a valuable tool in the solution of systematic conflicts in Metazoa that can aid molecular and external morphological analyses in ticks and, overall, provide more robust analyses and results. With this in mind, this study included histological analyses of the reproductive system of the species A. ovale and A. maculatum, as well as the description of morphohistological characters of the male reproductive system of ticks of the genus Amblyomma, in order to evaluate these characters within the current clustering proposals. In addition, 16S rDNA and COI (mitochondrial) molecular markers were used to study the genetic relationships of the species. The results show that the tick male reproductive system and its germ cells contain useful candidate characters for taxonomical analyses of Ixodida.

Bacteria of the genera Ehrlichia and Rickettsia in ticks of the family Ixodidae with medical importance in Argentina

The aim of this study was to get an overview about the occurrence of bacteria from the genus Ehrlichia and Rickettsia in ixodid ticks with medical importance in Argentina. Therefore, in 2013 and 2014, free-living ticks were collected in different provinces of northern Argentina. These ticks were determined as Amblyomma sculptum, Amblyomma neumanni, Amblyomma parvum, Amblyomma triste, Amblyomma ovale, Amblyomma tonelliae and Haemaphysalis juxtakochi. All samples were tested to determine the infection with Ehrlichia spp. and Rickettsia spp. by PCR assays. Rickettsial DNA was detected in all tested tick species, with the exception of A. tonelliae. 'Candidatus Rickettsia amblyommii', 'Candidatus Rickettsia andeanae', and Rickettsia parkeri were found in A. neumanni, A. parvum, and A. triste, respectively. Another rickettsial species, Rickettsia bellii, was found in A. sculptum, A. ovale and H. juxtakochi. None of the tested ticks showed infection with Ehrlichia. The results of the study demonstrate that Rickettsia species belonging to the spotted fever group are associated with various species of Amblyomma throughout a wide area of northern Argentina, where cases of Amblyomma ticks biting humans are common.

Rickettsia parkeri Rickettsiosis, Arizona, USA

In the United States, all previously reported cases of Rickettsia parkeri rickettsiosis have been linked to transmission by the Gulf Coast tick (Amblyomma maculatum). Here we describe 1 confirmed and 1 probable case of R. parkeri rickettsiosis acquired in a mountainous region of southern Arizona, well beyond the recognized geographic range of A. maculatum ticks. The likely vector for these 2 infections was identified as the Amblyomma triste tick, a Neotropical species only recently recognized in the United States. Identification of R. parkeri rickettsiosis in southern Arizona demonstrates a need for local ecologic and epidemiologic assessments to better understand geographic distribution and define public health risk. Education and outreach aimed at persons recreating or working in this region of southern Arizona would improve awareness and promote prevention of tickborne rickettsioses.

Dynamics of Exposure to Rickettsia parkeri in Cattle in the Paraná River Delta, Argentina

Several cases of human rickettsiosis caused by Rickettsia parkeri were recently documented in the Paraná River delta of Argentina, where the tick vector is Amblyomma triste Koch. As cattle suffer recurrent A. triste infestations, they are at risk of becoming infected with R. parkeri Herein we investigated the dynamics of R. parkeri and its A. triste vector in a herd of beef cattle. Cattle were followed for 18 mo and samples were analyzed for the presence of antibodies against four Rickettsia species (R. parkeri, Rickettsia bellii, Rickettsia amblyommii, and Rickettsia felis) and also for the presence of rickettsial DNA. Additionally, cattle were examined for attached ticks and questing adult ticks were collected. All ticks were analyzed for the presence of rickettsial DNA. No evidence of rickettsemia was found in any cow, but the high R. parkeri infection rate documented in A. triste both questing in the study area (13.9%) and feeding on cattle (19.8%) and the identification of antibodies against R. parkeri antigen in 90% of cattle are evidence that infection is taking place. Altogether, our data suggest that A. triste ticks are capable of naturally exposing cattle to R. parkeri However, the progress of R. parkeri infection and its impact on bovine health and production remain to be established.

Experimental vertical transmission of Rickettsia parkeri in the Gulf Coast tick, Amblyomma maculatum

Rickettsia parkeri, an obligate intracellular bacterium, is a member of the spotted fever group of rickettsiae (SFGR), and is transmitted to humans and other animals by invertebrate vectors. In the United States, the primary vector of R. parkeri is the Gulf Coast tick, Amblyomma maculatum Koch. This study investigates the vertical transmission dynamics of R. parkeri within a field-derived, naturally infected colony of A. maculatum. Transovarial and transstadial transmission of the pathogen was observed over three generations, with transovarial transmission efficiency averaging 83.7% and transstadial transmission rates approaching 100%. Fitness costs were determined by comparing reproduction values of the R. parkeri-infected A. maculatum colony to values from a R. parkeri-free colony. No significant reproductive fitness costs to the host ticks were detected in the R. parkeri-infected A. maculatum colony. Significantly fewer engorged F1 nymphs and F2 larvae of the R. parkeri-free colony succeeded in molting, suggesting that there may be some advantage to survival conferred by R. parkeri. The results of this study indicate that R. parkeri is maintained in A. maculatum populations efficiently by transovarial and transstadial transmission without any noticeable effects on tick reproduction or survival.

Ecology of the interaction between Ixodes loricatus (Acari: Ixodidae) and Akodon azarae (Rodentia: Criceridae)

The present study explores associations of different factors (i.e. host parameters, presence of other ectoparasites and [mainly biotic] environmental factors) with burdens of Ixodes loricatus immature stages in one of its main hosts in Argentina, the rodent Akodon azarae. For 2 years, rodents were trapped and sampled monthly at 16 points located in four different sites in the Parana River Delta region. Data were analysed with generalized linear mixed models with a negative binomial response (counts of larvae or nymphs). The independent variables assessed were (a) environmental: trapping year, presence of cattle, type of vegetation, rodent abundance; (b) host parameters: body length, sex, body condition, blood cell counts, natural antibody titers and (c) co-infestation with other ectoparasites. Two-way interaction terms deemed a priori as relevant were also included in the analysis. Most of the associations investigated were found significant, but in general, the direction and magnitude of the associations were context-dependent. An exception was the presence of cattle, which was consistently negatively associated with both larvae and nymphs independently of all other variables considered and had the strongest effect on tick burdens. Mites, fleas and Amblyomma triste were also significantly associated (mostly positively) with larval and nymph burdens, and in many cases, they influenced associations with environmental or host factors. Our findings strongly support that raising cattle may have a substantial impact on the dynamics of I. loricatus and that interactions within the ectoparasite community may be an important-but generally ignored-driver of tick dynamics.

Seroepidemiological survey of Rickettsia spp. in dogs from the endemic area of Rickettsia parkeri rickettsiosis in Uruguay

Rickettsia parkeri rickettsiosis is a vector-borne zoonosis that occurs in some countries of the American continent. Following the first description and determination of the pathogenicity to humans in 2004 in USA, this bacterium has been reported in several South American countries. Human cases have been diagnosed in both Uruguay and Argentina in the past years. This study consisted in a serosurvey of 1000 domestic dogs living in the endemic area of rickettsiosis in Uruguay, where Amblyomma triste is the tick vector. Sera were analyzed by Indirect Immunofluorescence Assay (IFA), against antigens of three different rickettsial species: R. rhipicephali, R. felis and R. parkeri. It was determined that 20.3% of the dogs had antibodies that reacted to at least one of the three species tested, taking as cut off ≥64 titers. Furthermore, 140 of the seropositive dogs (14%) had a titer at least 4 times higher to R. parkeri than those of any of the other species, thus, it was considered that the immune response was stimulated by that species in particular. This is the first serological survey in primary hosts for adults of A. triste in Uruguay, and therefore the first prevalence values are reported. Adult A. triste ticks collected from the environment as well as from dogs were analyzed by PCR in order to confirm the current circulation of the agent in the area. In this matter, two out of 28 ticks from dogs, and 3 out of 53 ticks from the environment were positive, and the corresponding sequence analysis revealed 100% similarity with R. parkeri strain maculatum.

The Evolving Medical and Veterinary Importance of the Gulf Coast tick (Acari: Ixodidae)

Amblyomma maculatum Koch (the Gulf Coast tick) is a three-host, ixodid tick that is distributed throughout much of the southeastern and south-central United States, as well as several countries throughout Central and South America. A considerable amount of scientific literature followed the original description of A. maculatum in 1844; nonetheless, the Gulf Coast tick was not recognized as a vector of any known pathogen of animals or humans for >150 years. It is now identified as the principal vector of Hepatozoon americanum, the agent responsible for American canine hepatozoonosis, and Rickettsia parkeri, the cause of an emerging, eschar-associated spotted fever group rickettsiosis identified throughout much of the Western Hemisphere. Coincident with these discoveries has been recognition that the geographical distribution of A. maculatum in the United States is far more extensive than described 70 yr ago, supporting the idea that range and abundance of certain tick species, particularly those with diverse host preferences, are not fixed in time or space, and may change over relatively short intervals. Renewed interest in the Gulf Coast tick reinforces the notion that the perceived importance of a particular tick species to human or animal health can be relatively fluid, and may shift dramatically with changes in the distribution and abundance of the arthropod, its vertebrate hosts, or the microbial agents that transit among these organisms.

Rickettsial Infection in Animals, Humans and Ticks in Paulicéia, Brazil

A previous study in Paulicéia Municipality, south-eastern Brazil, reported 9.7% of the Amblyomma triste ticks to be infected by Rickettsia parkeri, a bacterial pathogen that causes spotted fever in humans. These A. triste ticks were shown to be associated with marsh areas, where the marsh deer Blastocerus dichotomus is a primary host for this tick species. During 2008-2009, blood serum samples were collected from 140 horses, 41 dogs, 5 opossums (Didelphis albiventris) and 26 humans in farms from Pauliceia Municipality. Ticks were collected from these animals, from vegetation and from additional wildlife in these farms. Overall, 25% (35/140) of the horses, 7.3% (3/41) of the dogs, 3.8% (1/26) of the humans and 100% (5/5) of the opossums were seroreactive (titre ≥64) to spotted fever group (SFG) Rickettsia spp. Multivariate statistical analysis indicated that horses that were allowed to forage in the marsh were 4.8 times more likely to be seroreactive to spotted fever group (SFG) Rickettsia spp than horses that did not forage in the marsh. In addition, horses that had been living in the farm for more than 8.5 years were 2.8 times more likely to be seroreactive to SFG Rickettsia spp than horses that were living for ≤8.5 years. Ticks collected from domestic animals or from vegetation included Amblyomma cajennense, Amblyomma coelebs, Amblyomma dubitatum, Dermacentor nitens and Rhipicephalus microplus. By PCR analyses, only one pool of A. coelebs ticks from the vegetation was shown to be infected by rickettsiae, for which DNA sequencing revealed to be Rickettsia amblyommii. Ticks (not tested by PCR) collected from wildlife encompassed A. cajennense and Amblyomma rotundatum on lizards (Tupinambis sp), and A. cajennense and A. triste on the bird Laterallus viridis. Our results indicate that the marsh area of Paulicéia offers risks of infection by SFG rickettsiae.

Rickettsia parkeri rickettsiosis in different ecological regions of Argentina and its association with Amblyomma tigrinum as a potential vector

Rickettsia parkeri, a newly recognized tick-borne pathogen of humans in the Americas, is a confirmed cause of spotted fever group rickettsiosis in Argentina. Until recently, almost all cases of R. parkeri rickettsiosis in Argentina have originated from the Paraná River Delta, where entomological surveys have identified populations of R. parkeri-infected Amblyomma triste ticks. In this report, we describe confirmed cases of R. parkeri rickettsiosis from Córdoba and La Rioja provinces, which are located several hundred kilometers inland, and in a more arid ecological region, where A. triste ticks do not occur. Additionally, we identified questing A. tigrinum ticks naturally infected with R. parkeri in Córdoba province. These data provide evidence that another human-biting tick species serves as a potential vector of R. parkeri in Argentina and possibly, other countries of South America.

The sialotranscriptome of Amblyomma triste, Amblyomma parvum and Amblyomma cajennense ticks, uncovered by 454-based RNA-seq

Background

Tick salivary constituents antagonize inflammatory, immune and hemostatic host responses, favoring tick blood feeding and the establishment of tick-borne pathogens in hosts during hematophagy. Amblyomma triste, A. cajennense and A. parvum ticks are very important in veterinary and human health because they are vectors of the etiological agents for several diseases. Insights into the tick salivary components involved in blood feeding are essential to understanding vector-pathogen-host interactions, and transcriptional profiling of salivary glands is a powerful tool to do so. Here, we functionally annotated the sialotranscriptomes of these three Amblyomma species, which allowed comparisons between these and other hematophagous arthropod species.

Methods

mRNA from the salivary glands of A. triste, A. cajennense and A. parvum ticks fed on different host species were pyrosequenced on a 454-Roche platform to generate four A. triste (nymphs fed on guinea pigs and females fed on dogs) libraries, one A. cajennense (females fed on rabbits) library and one was A. parvum (females fed on dogs) library. Bioinformatic analyses used in-house programs with a customized pipeline employing standard assembly and alignment algorithms, protein databases and protein servers.

Results

Each library yielded an average of 100,000 reads, which were assembled to obtain contigs of coding sequences (CDSs). The sialotranscriptome analyses of A. triste, A. cajennense and A. parvum ticks produced 11,240, 4,604 and 3,796 CDSs, respectively. These CDSs were classified into over 100 distinct protein families with a wide range of putative functions involved in physiological and blood feeding processes and were catalogued in annotated, hyperlinked spreadsheets. We highlighted the putative transcripts encoding saliva components with critical roles during parasitism, such as anticoagulants, immunosuppressants and anti-inflammatory molecules. The salivary content underwent changes in the abundance and repertoire of many transcripts, which depended on the tick and host species.

Conclusions

The annotated sialotranscriptomes described herein richly expand the biological knowledge of these three Amblyomma species. These comprehensive databases will be useful for the characterization of salivary proteins and can be applied to control ticks and tick-borne diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/1756-3305-7-430) contains supplementary material, which is available to authorized users.

Taxonomic key to nymphs of the genus Amblyomma (Acari: Ixodidae) in Argentina, with description and redescription of the nymphal stage of four Amblyomma species

In the present study, we provide morphological descriptions of the nymph of Amblyomma parvitarsum, A. tonelliae, and redescriptions of A. argentinae and A. sculptum. A taxonomic key, with relevant morphological characters illustrated by scanning electron micrographs, is provided for nymphs of the 24 species of the genus Amblyomma occurring in Argentina. Species included are A. argentinae, A. aureolatum, A. auricularium, A. boeroi, A. brasiliense, A. calcaratum, A. coelebs, A. dissimile, A. dubitatum, A. incisum, A. longirostre, A. neumanni, A. nodosum, A. ovale, A. parvitarsum, A. parvum, A. pseudoconcolor, A. pseudoparvum, A. rotundatum, A. sculptum, A. tigrinum, A. tonelliae, A. triste and A. varium. Principal morphological characters used for discrimination among species are presence/absence of auriculae, cornua and festoons with tubercles, size and shape of spurs of coxa I, margin and punctations of scutum, shape of basis capituli and length of cervical grooves. The geographical distribution of each tick species included in this work is presented and the importance of an accurate determination to species level of the Amblyomma nymphs to make epidemiological inferences is also discussed.

Epidemiology of Rickettsia sp. strain Atlantic rainforest in a spotted fever-endemic area of southern Brazil

The present study was performed in Vila Itoupava, an area of the state of Santa Catarina, southern Brazil, in which a tick-borne spotted fever illness has been endemic since 2003. Notably, both the etiological agent and the vector of these spotted fever cases remain unknown. During January 2011, humans, domestic dogs, and their ticks were sampled in households that are typically surrounded by highly preserved Atlantic rainforest fragments. Ticks collected from dogs were Amblyomma ovale (34% prevalence), Amblyomma aureolatum (18.9%), and Rhipicephalus sanguineus (3.8%). A total of 7.8% (6/77) A. ovale and 9.3% (4/43) A. aureolatum were infected by Rickettsia sp. strain Atlantic rainforest, a Rickettsia parkeri-like agent recently shown to cause spotted fever illness in southeastern Brazil. Overall, 67.3% (35/52) of the dogs were seroreactive to spotted fever group rickettsiae, mostly with highest endpoint titers to R. parkeri. Among humans, 46.7% (7/15) reacted serologically to rickettsiae at low to moderate endpoint titers. Because canine seroreactivity to R. parkeri was strongly associated with frequent contact with forests (the preferred habitat for A. ovale and A. aureolatum), it is concluded that sampled dogs have been infected by strain Atlantic rainforest through the parasitism of these tick species. The present study provides epidemiological evidence that the spotted fever in the study area has been caused by Rickettsia sp. strain Atlantic rainforest, transmitted to humans by either A. ovale or A. aureolatum. Further studies encompassing direct diagnostic methods on clinical specimens from patients are needed to confirm the above epidemiological evidence.

Amblyomma parvitarsum (Acari: Ixodidae): localities, hosts and host-parasite ecology

Only a few aspects of the biology of Amblyomma parvitarsum Neumann are known. Adults of this hard tick species are parasites of South American camelids in the Andean plateau of Argentina, Bolivia, Peru and Chile and also in the Argentine Patagonia, but they have been also rarely found on other artyodactils and two species of birds. The larva has been collected from reptiles in northern Chile, whereas the hosts for the nymph remain unknown. On nine localities included within Altitude Tropical and Perarid Mediterranean ecoregions in northern Chile, we analyzed 237 reptiles, 285 birds, 624 rodents and 52 camelids for infestation with A. parvitarsum to calculate seasonal prevalence of this tick. We also reviewed the literature of this tick and three entomological collections for obtaining and summarizing all the information to date about this tick. None of the analyzed birds and rodents were parasitized with A. parvitarsum; however, seven over a total of ten reptile species that we caught were infested with the larva. In the camelid species Lama glama and Vicugna pacos we collected adult specimens of this tick. Larval prevalence was higher during fall (75 %) in Liolaemus pleopholis in the Altitude Tropical ecoregion. We also collected adult specimens of A. parvitarsum from camelid manure heaps during summer in Salar de Surire and Llullaillaco localities. Additionally, we also reviewed the literature of this tick and examined specimens in three entomological collections for obtaining and summarizing all the information to date about this tick. By this study, nine localities and seven new hosts are added for A. parvitarsum and we confirm reptiles as specific hosts of this tick larva.

Molecular identification of Rickettsia parkeri infecting Amblyomma triste ticks in an area of Argentina where cases of rickettsiosis were diagnosed

Specimens of the hard tick Amblyomma triste were found infected with Rickettsia parkeri in an area of Argentina (General Lavalle, Buenos Aires Province) where cases of human illness attributed to this microorganism have been reported. Molecular detection of R. parkeri was based on polymerase chain reactions that amplify a ca. 400-bp fragment of the 23S-5S intergenic spacer and a ca. 500-bp fragment of the gene encoding a 190-kDa outer membrane protein. Three (6.97%) of 43 A. triste ticks were determined to be positive for R. parkeri. These results provide strong evidence that A. triste is the vector of R. parkeri in the study area. The findings of this work have epidemiological relevance because human parasitism by A. triste ticks has been frequently recorded in some riparian areas of Argentina and Uruguay and new cases of R. parkeri rickettsiosis might arise in the South American localities where humans are exposed to the bites of this tick species.

A confirmed case of Rickettsia parkeri infection in a traveler from Uruguay

The first confirmed case of Rickettsia parkeri infection in Uruguay is reported. To date, in South America, molecularly confirmed cases of human infection have been found in Argentina and probably, Brazil. Our patient returned to Spain after a 7-day trip to Colonia Suiza (Southwestern Uruguay). He presented fever (39°C), chills, and two eschars (tache noire-like) surrounded by an indurated, erythematous halo on the inner side of the left ankle besides a maculopapular rash on the legs. After treatment with doxycycline for 7 days, he fully recovered. R. parkeri infection was diagnosed by molecular-based detection of the microorganism in a swab specimen of the eschar. Diagnosis was supported by seroconversion between acute- and convalescent-phase sera specimens.

Update on tick-borne rickettsioses around the world: a geographic approach

Tick-borne rickettsioses are caused by obligate intracellular bacteria belonging to the spotted fever group of the genus Rickettsia. These zoonoses are among the oldest known vector-borne diseases. However, in the past 25 years, the scope and importance of the recognized tick-associated rickettsial pathogens have increased dramatically, making this complex of diseases an ideal paradigm for the understanding of emerging and reemerging infections. Several species of tick-borne rickettsiae that were considered nonpathogenic for decades are now associated with human infections, and novel Rickettsia species of undetermined pathogenicity continue to be detected in or isolated from ticks around the world. This remarkable expansion of information has been driven largely by the use of molecular techniques that have facilitated the identification of novel and previously recognized rickettsiae in ticks. New approaches, such as swabbing of eschars to obtain material to be tested by PCR, have emerged in recent years and have played a role in describing emerging tick-borne rickettsioses. Here, we present the current knowledge on tick-borne rickettsiae and rickettsioses using a geographic approach toward the epidemiology of these diseases.

Old and new tick-borne rickettsioses

The field of rickettsiology is rapidly evolving. Rickettsiae are small Gram-negative bacteria that can be transmitted to humans by arthropods. In most cases they are transmitted transovarially in the arthropod; human beings are incidental hosts. In recent years the use of cell culture and molecular biology has profoundly changed our knowledge of rickettsiae and has led to the description of several new species. New rickettsial diseases have been found in three main situations: firstly, in places where no new species have been identified, typical rickettsial symptoms have been observed (Japan, China); secondly, typical rickettsioses have been found to be caused by different organisms - in such cases a new Rickettsia species has been misdiagnosed as a previously identified bacterium (for example, R. parkeri was confused with R. rickettsii); thirdly, atypical clinical symptoms have been found to be caused by rickettsial organisms such as R. slovaca. These findings challenge the old dogma that only one tick-borne rickettsiosis is prevalent in one geographical area. Many Rickettsia spp. have been identified in ticks, but have not yet been implicated in human pathology. These rickettsiae should be considered as potential pathogens. All known or suspected rickettsial diseases should be treated (including in children) with doxycycline.