Detection of Rickettsia rickettsii in saliva, hemolymph and triturated tissues of infected Dermacentor andersoni ticks by polymerase chain reaction.

The technique of polymerase chain reaction (PCR) is potentially superior to existing methods for detecting rickettsial infections in ticks. For this reason, we developed assays for identifying rickettsial infections in ticks by PCR. Our assays amplified a 500 bp fragment from the gene encoding the rOmp B protein of Rickettsia rickettsii. The selected primers amplified fragments of the predicted size from all spotted fever group rickettsiae (R. rickettsii, R. parkeri, R. conorii, R. sibirica) tested. No amplified products were detected when typhus group rickettsiae (R. canada, R. prowazekii, R. typhi) were assayed. Using techniques described in this study, we reliably amplified the predicted product from hemolymph, saliva and ground leg tissue samples from live, partially fed, infected ticks. Samples derived from infected ticks preserved in 70% ethanol also were suitable for amplification by PCR. Similar assays performed with infected ticks preserved in 5% buffered formalin seldom gave positive results.