Rickettsial infection in Amblyomma cajennense ticks and capybaras (Hydrochoerus hydrochaeris) in a Brazilian spotted fever-endemic area

Abstract

BackgroundBrazilian spotted fever (BSF), caused by the bacterium Rickettsia rickettsii, is the deadliest spotted fever of the world. In most of the BSF-endemic areas, capybaras (Hydrochoerus hydrochaeris) are the principal host for the tick Amblyomma cajennense, which is the main vector of BSF.MethodsIn 2012, a BSF case was confirmed in a child that was bitten by ticks in a residential park area inhabited by A. cajennense-infested capybaras in Itú municipality, southeastern Brazil. Host questing A. cajennense adult ticks were collected in the residential park and brought alive to the laboratory, where they were macerated and intraperitoneally inoculated into guinea pigs. A tick-inoculated guinea pig that presented high fever was euthanized and its internal organs were macerated and inoculated into additional guinea pigs (guinea pig passage). Tissue samples from guinea pig passages were also used to inoculate Vero cells through the shell vial technique. Infected cells were used for molecular characterization of the rickettsial isolate through PCR and DNA sequencing of fragments of three rickettsial genes (gltA, ompA, and ompB). Blood serum samples were collected from 172 capybaras that inhabited the residential park. Sera were tested through the immunofluorescence assay using R. rickettsii antigen.ResultsA tick-inoculated guinea pig presented high fever accompanied by scrotal reactions (edema and marked redness). These signs were reproduced by consecutive guinea pig passages. Rickettsia was successfully isolated in Vero cells that were inoculated with brain homogenate derived from a 3rd passage-febrile guinea pig. Molecular characterization of this rickettsial isolate (designated as strain ITU) yielded DNA sequences that were all 100% identical to corresponding sequences of R. rickettsii in Genbank. A total of 83 (48.3%) out of 172 capybaras were seroreactive to R. rickettsii, with endpoint titers ranging from 64 to 8192.ConclusionsA viable isolate of R. rickettsii was obtained from the tick A. cajennense, comprising the first viable R. rickettsi isolate from this tick species during the last 60 years. Nearly half of the capybara population of the residential park was seroreactive to R. rickettsii, corroborating the findings that the local A. cajennense population was infected by R. rickettsii.

Risk factors associated with the transmissionof Brazilian spotted fever in the Piracicaba river basin, State of São Paulo, Brazil

“…Rickettsia rickettsii was recently isolated in Amblyomma sculptum ticks collected in capybaras in a residential condominium in an endemic area of São Paulo, thus confi rming the aforementioned assumptions (27) . The association of confi rmed cases in the presence of capybaras in this study is consistent because the investigation of all suspected cases of BSF occurred in situations with clinical evidence and an epidemiological history of disease, including contact with hazardous environments and the presence of host species.…”

Ticks (Acari: Ixodidae) as ectoparasites of Brazilian wild birds and their association with rickettsial diseases

“…sculptum is a very aggressive tick to humans and the main vector of R. rickettsii to humans causing the lethal disease known as Brazilian spotted fever (SZABÓ et al, 2013a;KRAWCZAK et al, 2014).…”

Seroprevalence of rickettsia spp. and a study of the tick fauna in dogs from the municipality of Seropédica, State of Rio de Janeiro

“…It is currently considered a disease for which notification is compulsory, and Amblyomma sculptum (previously referred to as Amblyomma cajennense) and Amblyomma aureolatum ticks are the main transmission vectors (PINTER; LABRUNA, 2006;KRAWCZAK et al, 2014). Dogs are frequently parasitized by these tick species and are therefore important sentinels for disease surveillance (PAROLA et al, 2013).…”