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Sixty-two questing adult Rhipicephalus sanguineus (Latreille) ticks were collected by direct removal from blades of turfgrass and adjacent concrete walkways at a suburban home in Riverside County, CA, and tested for the presence of Rickettsia, Bartonella, and Ehrlichia DNA. Polymerase chain reaction (PCR) was used to amplify fragments of the 17-kDa antigen gene and the rOmpA gene of the spotted fever group rickettsiae. One male tick contained R. rickettsii DNA; its genotype differed from R. rickettsii isolates found in Montana and Arizona that cause Rocky Mountain spotted fever and from Hlp#2 and 364D serotypes. One male tick and one female tick contained B. henselae DNA. No Ehrlichia platys or Ehrlichia canis DNAs were detected using nested PCR for their 16S rRNA genes. These findings extend the area where Rickettsia rickettsii may be vectored by Rh. sanguineus. Rh. sanguineus also may be infected with Bartonella henselae, a human pathogen that is typically associated with fleas and causes cat scratch disease.

A rickettsial survey of ixodid ticks known to bite man was conducted in 1979 in four coastal counties of California to obtain isolates from tick species that might be involved in the transmission of spotted fever-like illnesses, and to examine serologic characteristics of the rickettsiae relative to defined members of the spotted fever group (SFG). One hundred and seventy (19.4%) of 877 ticks comprising three species were shown by hemolymph test to harbor rickettsia-like organisms. A total of 85 SFG rickettsia isolates was obtained by Vero-cell culture; 82 were from Dermacentor occidentalis, two were from D. variabilis, and one was from Ixodes pacificus. As determined by microimmunofluorescence, the isolates comprised four distinct serotypes. Two serotypes were obtained only from D. occidentalis, and one each only from D. variabilis and I. pacificus, respectively. Most D. occidentalis isolates possessed the serologic characteristics of Rickettsia rhipicephali, but there were similar to yet distinguishable from, R. rickettsii and are members of an unclassified serotype referred to as 364D. The two isolates from D. variabilis resembled the unclassified 369C serotype previously shown to be associated with this species and D. andersoni elsewhere in the United States. The I. pacificus isolate was similar to strains of the unclassified Tillamook serotype isolated from this tick in several localities in western Oregon. Representative strains of the four serotypes could also be distinguished on the basis of pathogenicity for Vero cells, chick embryos, guinea pigs, and/or meadow voles. The significance of these findings relative to occurrence of tick-associated illnesses in western California is briefly discussed.