Seroprevalence and risk factors for Rickettsia felis exposure in dogs from Southeast Queensland and the Northern Territory, Australia

Background: The recent detection of Rickettsia felis DNA in dogs in Australia suggests that dogs are potential mammalian reservoir hosts for this emerging rickettsia. To date, there is no published report addressing the seroprevalence of R. felis in dogs in Australia. Methods: Antigens for R. felis were produced by inoculating confluent XTC-2 monolayer cell cultures with three pools of cat flea (Ctenocephalides felis) homogenates. Infection was confirmed by real-time (qPCR), conventional or nested PCRs targeting the ompB, gltA, 17 kDa and ompA genes. Two hundred and ninety-two dogs from Southeast Queensland and the Northern Territory were tested for the presence of R. felis antibodies using a microimmunofluorescence (IF) test and the seroprevalence and associated risk factors for exposure were determined using both uni- and multi-variate analyses. Results: Rickettsia felis was successfully isolated in cell culture from all three cat-flea pools. One hundred and forty-eight dogs (50.7%) showed seropositivity with titres >= 64 and 54 (18.5%) with titres >= 128. At antibody titres >= 64, dogs with active ectoparasite control were less likely to be seropositive to R. felis (OR: 2.60; 95% CI: 1.20 - 5.56). Conclusions: This first reported isolation of R. felis in cell culture in Australia allowed for the production of antigen for serological testing of dogs. Results of this serological testing reflects the ubiquitous exposure of dogs to R. felis and advocate for owner vigilance with regards to ectoparasite control on domestic pets.