Tickborne microorganisms in Dermacentor andersoni (Acari: Ixodidae) in the Bitterroot Mountains of Western Montana.

The Rocky Mountain wood tick, Dermacentor andersoni Stiles, is the most common human biting tick in the Rocky Mountain region of the USA. Although Rickettsia spp. and Colorado tick fever virus have been studied in D. andersoni in certain areas of their distribution, investigations of most other tickborne pathogens are lacking. Despite the history of Rocky Mountain spotted fever in the Bitterroot Mountains of western Montana, no comprehensive surveys of large numbers of ticks for Rickettsia spp. have been conducted there for >40 years. For the present study, host-seeking adult D. andersoni were collected at multiple sites in canyons on the west side of the Bitterroot Valley in western Montana in spring 2021. Following DNA extraction, ticks were screened by polymerase chain reaction assays for several tick-borne microorganisms. DNA sequence data analysis was conducted to confirm identity and conduct phylogenetic comparisons with reference strain sequences of different organisms. No ticks were found to contain Anaplasma spp., Borrelia spp., or Ehrlichia spp. DNA, and a Babesia sp. was detected in only one tick. However, Bartonella spp. DNA was detected in 2 % of tested ticks. Additionally, five species of Rickettsia, including R. peacockii, R. bellii, R. rhipicephali, R. montanensis, and R. rickettsii, were identified in ticks from different sites. The most prevalent Rickettsia species was R. peacockii and the least common was R. rickettsii (found in only two ticks). The relevance of these findings is discussed in relation to historical and contemporary data on Bartonella spp. and Rickettsia spp.