Detection and Identification of Spotted Fever Group Rickettsiae in Dermacentor Species from Southern California

Abstract

Dermacentor occidentalis Marx and Dermacentor variabilis (Say) commonly bite humans in California. These Dermacentor species may play a role in transmitting spotted fever group (SFG) rickettsiae to humans in many parts of the state where Dermacentor andersoni Stiles, a known vector for the etiologic agent of Rocky Mountain spotted fever, Rickettsia rickettsii, is absent. However, the specic rickettsial agents present in these ticks and their current prevalence are poorly understood. In total, 365 D. occidentalis and 10 D. variabilis were collected by agging vegetation at 16 sites in ve counties of southern California. The presence of SFG rickettsial DNA in these ticks was detected with rOmpA and GltA gene polymerase chain reaction (PCR) assays. The rickettsial species were identied by sequencing PCR amplicons. Of 365 D. occidentalis, 90 (24.7%) contained R. rhipicephali DNA, 28 (7.7%) contained DNA of unclassied genotype 364D, two (0.55%) contained R. bellii DNA, and one (0.3%) contained R. rickettsii DNA. Of 10 D. variabilis, four (40%) contained only R. rhipicephali. Four new genotypes of R. rhipicephali were discovered. For the rst time, we detected R. rickettsii in D. occidentalis. Our study provides the rst molecular data on the prevalence and species identication of SFG rickettsiae circulating in populations of these California ticks. Because neither D. variabilis nor R. rickettsii were abundant, 364D should be evaluated further as a potential cause of human SFG rickettsioses in southern California.