Low exposure of dogs to ticks and Rickettsia spp. in the vicinity of the largest inland Atlantic rainforest remnant in Southern Brazil

Dogs accessing natural areas in Brazil are exposed to tick species typically associated with wild carnivores, some of which are vectors of pathogenic Rickettsia. Infested dogs may transport ticks into households and act as amplifying hosts for these agents. Iguaçu National Park (INP), a major inland Atlantic Forest reserve in Brazil, harbors at least nine tick species and five Rickettsia species. This study evaluated tick infestation in 116 rural dogs from properties along most of the 420 km perimeter of INP and 22 urban dogs from forest-adjacent areas in Foz do Iguaçu. Sera from 39 dogs were tested against five Rickettsia antigens using an indirect immunofluorescence assay. A total of 169 ticks were collected, including Rhipicephalus linnaei (n=87), Amblyomma ovale (n=62), Amblyomma coelebs (n=5), and Rhipicephalus microplus (n=3), with an overall infestation prevalence of 28.3%. Seroprevalence against Rickettsia spp. was 42.9% in rural dogs and 18.1% in urban dogs. The highest titers were 1:512 in rural dogs (against R. parkeri, R. amblyommatis, and R. rhipicephali) and 1:256 in urban dogs (against R. rickettsii), while median titers were zero. Both tick infestation and Rickettsia exposure were lower than those reported in dogs from other Atlantic Forest regions. These findings suggest an overall limited exposure of free-ranging dogs to ticks and Rickettsia spp. Further investigation is needed to understand the causes of this low exposure, including the potential influence of the jaguar population and other wild carnivores in INP, which may restrict dog access to forested areas.