Domestic Dogs (Canis familiaris) as Reservoir Hosts for Rickettsia conorii

Rickettsia conorii is the causative agent of Mediterranean spotted fever (MSF) and Israeli spotted fever (ISF) transmitted by the brown dog tick Rhipicephalus sanguineus. In areas where MSF or ISF are prevalent, dogs have high prevalence of R. conorii-neutralizing antibodies. However, the true role of dogs in the persistence of the R. conorii transmission cycle is unknown, and their reservoir competence for this pathogen has remained untested. We assessed the ability of dogs infected with R. conorii to transmit the pathogen to previously uninfected Rh. sanguineus ticks. Dogs were infected either via needle-inoculation of cultured rickettsiae or naturally via infected tick bite. Dogs were monitored for clinical signs of infection, for rickettsemia by PCR, and for seroconversion and were subjected to infestation with uninfected ticks at different time points. Rh. sanguineus larvae and nymphs successfully acquired the agent from both needle-inoculated and tick-infected dogs and transmitted it transtadially. Tick-infected dogs remained infectious to ticks for at least a month postinfection. The molted ticks were, in turn, infectious to naive dogs. These results demonstrate that dogs are capable of acquiring R. conorii from infected Rh. sanguineus ticks and transmitting infection to cohorts of uninfected ticks, thus confirming for the first time that dogs are indeed competent reservoirs for R. conorii. In addition, dogs with different genetic backgrounds appear to differ in their susceptibility to R. conorii infection.