Exploring rickettsial pathogens in ticks of Northern Arizona
Rickettsia rickettsii is the causative agent of Rocky Mountain spotted fever (RMSF), a vector-borne disease transmitted by the brown dog tick, Rhipicephalus sanguineus. R. rickettsii is maintained in a vector-host cycle between R. sanguineus and dog populations in Arizona. Since the first case of RMSF in Arizona in 2003, there have been cases reported in the state annually, with an increase in recent years. The rise in cases could be attributed to an increase in habitat of R. sanguineus populations due to climate change. In addition to R. rickettsii, ticks contain a variety of endosymbiont non-pathogenic bacteria and can vector other spotted-fever group Rickettsia that cause spotted fever-like disease. We set out to assess the prevalence of R. rickettsii and other spotted fever group Rickettsia in Northern Arizona R. sanguineus populations. After pooling samples, we conducted real-time PCR, traditional PCR, and sequencing to test for the presence of pathogenic and non-pathogenic Rickettsia species. Through qPCR we found, 10% of the tested tick pools contained high concentrations of Rickettsia. Of these, 9 were positive for spotted fever group Rickettsia. Through sequencing, we identified Rickettsia massiliae, a spotted fever group Rickettsia, in three samples. The presence of spotted fever-like disease causing bacteria in Arizona tick populations demonstrates a need for increased tick-borne pathogen surveillance.
