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

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

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

Molecular Detection of Candidatus Rickettsia andeanae and Ehrlichia sp. in Amblyomma pseudoconcolor Aragão, 1908 (Acari: Ixodidae) from the Argentinian Patagonia

This study presents the molecular detection of Candidatus Rickettsia andeanae and Ehrlichia sp. in Amblyomma pseudoconcolor Aragão, 1908 (Acari: Ixodidae) collected on a large hairy armadillo (Chaetophractus villosus (Desmarest, 1804)). On 12 October 2020, a specimen of C. villosus was found dead on the road in Río Negro province, Argentina. Molecular detection of Rickettsia and Ehrlichia agents was performed amplifying the gltA and 16S rRNA gene, respectively. One tick, determined morphologically and genetically as A. pseudoconcolor, was collected on C. villosus. The rickettsial agent detected in A. pseudoconcolor was identified as Candidatus Rickettsia andeanae. The Ehrlichia sp. strain showed high sequence similarity to different uncultured Ehrlichia sp. detected in horses, capybaras and Ixodes ornithorhynchi from Nicaragua, Brazil and Australia, respectively. The results of this study and previous findings suggest that A. pseudoconcolor may be a potential vector of some Rickettsia and Ehrlichia bacteria of unknown pathogenicity.

Occurrence of tick-borne pathogens in dogs in a coastal region of the state of Ceará, northeastern Brazil

The aim of this study was to determine the occurrence of tick-borne pathogens (Ehrlichia canis, Babesia vogeli, Hepatozoon spp. and Rickettsia spp.) in dogs in Vila de Jericoacoara, coastal region of Ceará, Brazil. Blood samples were collected from 153 animals and analyzed using molecular and serological methods. Sixty animals were found to be infected or exposed to at least one of the pathogens studied. Babesia vogeli was the most prevalent pathogen (15%), followed by E. canis (13.7%) and Hepatozoon spp. (11.8%), which was identified as Hepatozoon canis through sequencing. Twenty dogs (13%) were seroreactive to Rickettsia spp. Rhipicephalus sanguineus sensu lato was observed on 11.8% of the animals. There were associations between age (< 3 years old) and positivity for B. vogeli, and between habitation (stray dogs) and positivity for H. canis. There were also associations between anemia and infection with H. canis, and between leukopenia and exposure to Rickettsia spp. No association was detected between clinical alterations and infection with or exposure to the pathogens studied. The results confirmed that pathogens of veterinary importance are circulating in northeastern Brazil and showed that dogs are exposed to Rickettsia species with zoonotic potential, thus indicating a need for vector control measures.

Rickettsial infection in free-ranging capybaras (Hydrochoerus hydrochaeris) and their ticks (Acari, Ixodidae) in the Caatinga and Atlantic forest biomes, Northeastern Brazil

Caatinga and Atlantic Forest are Brazilian biomes threatened by anthropogenic disturbances, which are a serious threat to biodiversity and favor the emergence of zoonotic pathogens. Capybara populations are increasingly present in urban and rural areas due to the loss of their natural habitats. There are no studies on the rickettsial infection in these rodents in Northeastern Brazil, although there are case records of Brazilian Spotted Fever (BSF) in this region. In this context, we evaluated rickettsial infection in capybaras and their ticks in four areas of the Atlantic Forest and Caatinga biomes in Northeastern Brazil. Blood sera from 21 capybaras were tested by indirect immunofluorescence assay (IFA) using Rickettsia rickettsii, R. parkeri, and R. amblyommatis antigens. Blood samples and ticks (Amblyomma sp., Amblyomma dubitatum and Amblyomma sculptum) were tested by PCR, targeting a fragment of the rickettsial gltA gene and R. bellii primers. Overall, 15 out of 21 capybaras (71.4%) reacted positively (titer ≥64) to at least one of the three Rickettsia antigens tested, with final titers ranging from 64 to 1024. No rickettsial DNA was found in capybara blood samples. Rickettsial DNA was detected in 22 of 31 adult tick pools using gltA gene, being all nine pools of A. sculptum and 16 of the 19 of A. dubitatum, but all samples were negative to R. bellii specific primers. All attempts to sequence the amplicon were unsuccessful, indicating a possible low rickettsial load in the tick samples. The present study reports for the first time the serological evidence of Rickettsia spp. infection in free-ranging capybaras and suggest the rickettsial infection in A. sculptum and A. dubitatum in the Caatinga and Atlantic Forest biomes in Northeastern Brazil.

Identification of tick-borne pathogens using metagenomic analyses in H. longicornis feeding on humans in downtown Beijing

On August 14th, 2018, a Beijing resident living in Xicheng District found a female H. longicornis tick attached to the skin at the front of his upper shin. On examination, the patient was afebrile and appeared well. The species of the tick was identified through morphological characteristics and phylogenetic analysis based on cytochrome C oxidase subunit I. This H. longicornis tick was screened for tick-borne pathogens such as viruses, bacteria and parasites. RNA pathogens were screened by PCR and sequencing, while DNA pathogens were screened by metagenomic analyses. It was found that the tick was positive for the DNA sequences of zoonotic and animal pathogens such as A. phagocytophilum, Ehrlichia minasensis and C. burnetii. Considering the good health condition of the patient, we hypothesized that the pathogens originated from the tick specimen itself rather than host blood meal. For the first time, our study reveals the possible risk of transmission of tick-borne pathogens to human beings through tick bit in downtown Beijing. Further research is needed to screen for tick-borne pathogens among unfed ticks collected from central Beijing.

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

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

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

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

Phenology of Amblyomma sculptum in a degraded area of Atlantic rainforest in north-eastern Brazil

Amblyomma sculptum is the principal vector of Rickettsia rickettsii, the main agent of spotted fever rickettsiosis in Brazil. Little information is available regarding the population dynamics of this tick in some regions, including north-eastern Brazil, where cases of spotted fever rickettsioses are increasingly reported. Herein, we studied the phenology of A. sculptum in a rural area in north-eastern Brazil. Ticks were collected from the environment, using dry ice-baited traps, monthly for two consecutive years. In total, 1500 ticks were collected: 94 females (6.3%), 74 males (4.9%), 468 nymphs (31.2%), and 864 larvae (57.6%). All nymphs and females were identified as A. sculptum. Males were tentatively identified as A. sculptum and larvae as Amblyomma spp. Ticks were more numerous during spring and summer, followed by autumn and winter. Peaks of larvae and nymphs were recorded during summer and spring, respectively, whereas adults were more frequently collected in spring. A total of 380 ticks were tested by PCR for the gltA gene of Rickettsia spp., but none of them were positive. While our results revealed a seasonal pattern for A. sculptum in north-eastern Brazil that is distinct from the seasonal pattern in south-eastern Brazil, we caution that the observed pattern could have been biased by the relatively low number of ticks collected. Finally, the absence of Rickettsia-infected ticks does not rule out the possibility that rickettsial organisms are circulating in the study area and further long-term studies are warranted.

Detection of Rickettsia spp. in ticks associated to wild mammals in Northeastern Brazil, with notes on an undetermined Ornithodoros sp. collected from marsupials

We report tick infestations and rickettsial detection in ticks infesting free-living wild mammals (Monodelphis domestica, Tolypeutes tricinctus, Thrichomys inermis and Kerodon rupestris) captured in the Caatinga ecoregion of Bahia state, northeastern Brazil, during September to December 2016. Overall, 117 ticks (61 larvae, 25 nymphs, 25 males, 6 females) belonging to two genera, and at least three species were collected: Amblyomma auricularium, Amblyomma parvum, Amblyomma sp., Ornithodoros rietcorreai and an unidentified Ornithodoros sp. We provide new host records to the rodent T. inermis parasitized by larva and nymphs of A. auricularium and to the marsupial M. domestica infested by larvae of A. auricularium. Furthermore, we describe new tick-host association for larvae of O. rietcorreai on the rodents K. rupestris and T. inermis. Concerning tick-Rickettsia associations, we detected Rickettsia amblyommatis and an uncharacterized species of Rickettsia belonging to the spotted fever group (SFG) in both A. auricularium and A. parvum. Additionally, 'Candidatus Rickettsia andeanae' was detected in A. parvum as well.

Fatal case of spotted fever in a patient from Northeastern Brazil

Spotted fevers are diseases caused by bacterial agents belonging to the spotted-fever (SF) group of the genus Rickettsia. The first documented case of SF in Pernambuco State, Northeast Brazil, was reported here. Also, it is the first case described of fatal SF in Northeast region of Brazil. The patient was a resident of Arcoverde municipality and the probable site of infection lies in Sertania municipality, both in Pernambuco State, a semi-arid region of Brazil. The patient had not visited other areas where SF is endemic. The patient showed clinical manifestations and epidemiological exposure compatible with SF, and the infection was confirmed by molecular biology techniques.