Vector Tick Transmission Model of Spotted Fever Rickettsiosis

Abstract Many aspects of rickettsial infections have been characterized, including pathogenic and immune pathways, as well as mechanisms of rickettsial survival within the vertebrate host and tick vector. However, there is a remarkable paucity of studies focused on the complex pathogen-vector-host interactions during tick feeding. Therefore, our objective was to develop a tick transmission model of spotted fever group rickettsial infection to study the initial events in disease development. The most appropriate strain of mouse was identified to be evaluated as a transmission model, and the course of infection, bacterial levels, histopathologic changes, and antibody response during tick transmission in mice infested with Amblyomma maculatum ticks carrying the emerging pathogen, Rickettia parkeri, were further studied. The results demonstrated distinct clinical signs in C3H/HeN mice infected intravenously, leading to selection of this mouse strain for tick transmission studies. Active infection of animals was observed after tick vector transmission. The bacteria disseminated systemically and had spread to several organs at 24 hours post tick attachment (p.t.a.), with peak bacterial load at day 6 p.t.a. Skin, lung, and liver showed the greatest pathologic changes with inflammatory cellular infiltration and necrosis. These findings indicate the feasibility of using murine infection with R. parkeri by A. maculatum tick transmission as a model to study different aspects of spotted fever group rickettsial disease establishment.