Detection of Ehrlichia, Francisella, and Rickettsia in Dermacentor Ticks in Eastern Washington

Dermacentor ticks are widespread in eastern Washington and are known vectors of bacterial pathogens and harborers of endosymbionts belonging to the genera Francisella and Rickettsia. Some Dermacentor species can become infected with Ehrlichia chaffeensis Anderson et al. (Rickettsiales: Ehrlichiaceae); it remains unclear if any are competent vectors for this bacterial pathogen. This study reports the abundance of Dermacentor species and prevalence of select tick-borne bacterial pathogens collected from two conservation areas popular among hikers in Spokane County, Washington. In total, DNA from 599 adult ticks was analyzed using PCR; 87.8% (526/599) were identified as Dermacentor andersoni Stiles and 12.2% (73/599) as D. similis Lado, Glon and Klompen (Ixodida: Ixodidae). Ticks were also screened for the presence of bacterial DNA using genus- or species-specific primers targeting Rickettsia spp., Francisella spp., and E. chaffeensis. Rickettsia endosymbionts, R. peacockii Niebylski et al. or R. rhipicephali (Burgdorfer et al.) Weiss and Moulder (Rickettsiales: Rickettsiaceae), were found in 4.0% (21/526) of D. andersoni. Francisella-like endosymbionts were detected in 65.9% (395/599) of all ticks. No species known to be pathogenic belonging to either Rickettsia or Francisella were detected. However, E. chaffeensis was detected in 15.3% (12/73) of D. similis, which to our knowledge is the first report of ticks harboring this species of bacteria in Washington state. These findings contribute to understanding the microbial ecology of ticks in the Inland Northwest.