Isolation and Identification of<i>Rickettsia massiliae</i>from<i>Rhipicephalus sanguineus</i>Ticks Collected in Arizona

TLDR

The pathogenicity and infectious potential of *Rickettsia massiliae* AZT80 in dogs and humans in the United States remain unknown. Twenty *Rhipicephalus sanguineus* ticks from eastern Arizona were screened by PCR, and one rickettsial isolate was obtained by inoculating triturated tick material into Vero E6 and XTC‑2 cell monolayers for culture and genotypic analysis. Five ticks (25%) tested positive for Rickettsia DNA, and the isolated AZT80 strain matched *R. massiliae* strain Bar29 with >99% gene similarity, was non‑cytotoxic in Vero cells, persisted in XTC‑2 cells, and was susceptible to doxycycline but resistant to rifampin and erythromycin.

Abstract

Twenty Rhipicephalus sanguineus ticks collected in eastern Arizona were tested by PCR assay to establish their infection rate with spotted fever group rickettsiae. With a nested PCR assay which detects a fragment of the Rickettsia genus-specific 17-kDa antigen gene (htrA), five ticks (25%) were found to contain rickettsial DNA. One rickettsial isolate was obtained from these ticks by inoculating a suspension of a triturated tick into monolayers of Vero E6 monkey kidney cells and XTC-2 clawed toad cells, and its cell culture and genotypic characteristics were determined. Fragments of the 16S rRNA, GltA, rOmpA, rOmpB, and Sca4 genes had 100%, 100%, 99%, 99%, and 99%, respectively, nucleotide similarity to Rickettsia massiliae strain Bar29, previously isolated from R. sanguineus in Catalonia, Spain (L. Beati et al., J. Clin. Microbiol. 34:2688-2694, 1996). The new isolate, AZT80, does not elicit cytotoxic effects in Vero cells and causes a persistent infection in XTC-2 cells. The AZT80 strain is susceptible to doxycycline but resistant to rifampin and erythromycin. Whether R. massiliae AZT80 is pathogenic or infectious for dogs and humans or can cause seroconversion to spotted fever group antigens in the United States is unknown.