Development and characterization of a murine model of Rickettsia parkeri rickettsiosis

Abstract

Rickettsia parkeri, a member of the spotted fever group of Rickettsia, is the agent of an emerging rickettsiosis in the southeastern United States and South America. Despite increased recognition of human cases, limited information is available regarding infection of invertebrate and vertebrate hosts for this emerging tick-borne disease. Towards development of a viable transmission model and to further characterize the pathology associated with R. parkeri infection, inbred mouse strains (A/J, Balb/C, C3H/HeJ, and C3H/HeN) were intravenously and intradermally inoculated with R. parkeri. The C3H/HeJ strain of mice were identified as the most susceptible to R. parkeri infection and were found to develop eschar-like lesion at the site of intradermal inoculation in the tail. These mice were further utilized to test the effect of tick feeding on the proliferation of R. parkeri at the intradermal inoculation site. Ticks were allowed to feed over the site of intradermal inoculation of R. parkeri at the nape of the neck. Rickettsial proliferation was significantly increased by tick feeding, suggesting a role for ticks as more than just fomites. Finally, the natural ecology of R. parkeri was investigated by screening domestic dogs in temporary housing situations for the presence of Rickettsia using PCR for the genus specific 17 kDa antigen gene. The more specific primers for rompA were utilized for PCR on the 12 positive samples identified by the screening PCR. After sequencing, the rompA amplicons were identified as R. parkeri, indicating a role for dogs in the ecology of R. parkeri and as a potential risk factor for development of human disease. Continued study into the pathogenesis of R. parkeri rickettsiosis in the murine model, the influence of tick saliva on rickettsial proliferation, and the role of dogs in the natural ecology of R. parkeri will lead to a better understanding of this emerging tick-borne rickettsiosis.