Anti-Rickettsia rickettsii antibodies in capybaras (Hydrochoerus hydrochaeris Linnaeus, 1766) from an agricultural landscape in Araras, São Paulo, Brazil

Spotted fever is a typically endemic infectious disease caused by rickettsiae from the spotted fever group, of which Rickettsia rickettsii is the main etiologic agent. It presents high mortality rates in Brazil, with transmission to humans or animals through the bite of infected ticks. The capybara (Hydrochoerus hydrochaeris) is an important reservoir for Rickettsia spp.; these bacteria can circulate in an infected animal presenting only fever as a clinical sign of the disease, as demonstrated by experimental infection. Considering the high zoonotic potential and the damage caused to human, animal, and environmental health, this study searched for anti-Rickettsia rickettsii antibodies in capybaras from an agricultural landscape in the city of Araras, State of São Paulo, Brazil. The indirect immunofluorescence (IFA) technique was used to detect anti-R. rickettsii antibodies. From the 28 serum samples tested using IFA, 18 (64.28%) were considered reactive, with antibody titers ranging from 256 to 2048. Seven (38.88%) samples presented titers of 256, three (16.67%) with titers of 512, five (27.78%) with titers of 1024, and three (16.67%) with titers of 2048. However, it was not possible to significantly associate gender to these serologic results. These results demonstrate that at some point during their lives, the studied capybaras were exposed to the etiologic agent, but it is impossible to know when this occurred. Further studies need to be performed to clarify which serological titers ensure an infection in capybaras, based on clinical and laboratory assessment of rickettsemia, and to establish the relationship between titers and the chronicity of disease. This is necessary owing to the possibility of cross-reactions with other rickettsiae species of the same subgroup, leading to the need for molecular tests to confirm diagnosis.