Rickettsia spp. in Five Tick Species Collected in Central California

Tick-borne disease surveillance in North America has long focused on Lyme disease, though there is currently a significant shift towards comprehensive pathogen surveillance in ticks. Central California has often been overlooked in regular tick-borne pathogen surveillance despite the presence of numerous medically important tick species. The bacterial genus Rickettsia contains tick-borne species that are known pathogens, such as those in the spotted fever group; nonpathogenic endosymbionts; and many species with unknown pathogenic potential. Five common tick species (Ixodes pacificus Cooley and Kohls [Acari: Ixodidae], Dermacentor occidentalis Marx [Acari: Ixodidae], D. variabilis Say, Rhipicephalus sanguineus Latreille [Acari: Ixodidae], and Ornithodoros parkeri Cooley [Acari: Argasidae]) of California were collected by both traditional and modern techniques, and subsequently screened for Rickettsia spp. Many individuals from all five tick species were PCR positive for Rickettsia spp., and a combination of species-specific primers, a restriction fragment length polymorphism assay, and DNA sequencing was used to further characterize the species composition in these ticks. Probable Rickettsia philipii (Rickettsia 364D) was detected in one (1.56%) D. occidentalis collected in Fresno County; R. rhipicephali was detected in 23.4% of D. occidentalis from Fresno Co.; R. bellii was detected in 88.2% of D. variabilis, 7.8% of D. occidentalis, and in one R. rhipicephalus (1.1%) from Fresno Co.; R. monacensis str. Humboldt was detected in three (100%) of I. pacificus collected in both Fresno and Madera Co.; and an uncharacterized Rickettsia was detected in (26.4%) of O. parkeri collected in both Fresno and Madera Co. The findings in this study highlight the need for ongoing surveillance in this region of California.

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