Absence of Rickettsia rickettsii and Occurrence of Other Spotted Fever Group Rickettsiae in Ticks from Tennessee

Rocky Mountain spotted fever (RMSF) is the most common tick-borne illness in Tennessee Little is known about the occurrence of R. rickettsu the causative agent. in ticks in Tennessee To better understand the prevalence and distribution of rickettsial agents in ticks, we tested 1,265 Amblyomma. Dermacentor. and Ixodes adult and nymphal ticks. Additionally, we tested 231 Amblyomma americanum larvae Ticks were collected from 49 counties from humans, wild animals, domestic canines. and flannel drags. Spotted fever group rickettsiae (SFGR) DNA was detected by polymerase chain reaction (PCR) in 32% of adult and nymphal ticks A total minimum infection rate of 85 63 was found in larval pools tested. Three rickettsia! species. Rickettsia montana. Rickettsia amblyompm, and Rickettsia cooleyi were identified by molecular analysis Rickettsra rick-emu was not detected This study suggests that some RMSF cases reported in Tennessee may be caused by cross-reactivity with other SFGR antigenically related to R rickettsu.