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Rickettsia Tillamookensis from Ixodes Pacificus Found in Several California Counties

A study in Journal of Medical Entomology by Christopher D. Paddock, et al., took a deeper look into Rickettsia tillamookensis (Rickettsiales: Rickettsiaceae), a unique Rickettsia species that may possibly be pathogenic and occurs in I. pacificus (Acari: Ixodidae), the Western blacklegged tick. The R. tillamookensis agent was first mentioned in 1978 and has been recently recognized as a novel transitional group agent. Historically, incidence rates and distribution levels of R. tillamookensis have been widely unknown.

Rickettsia Tillamookensis
Western blacklegged tick (Ixodes pacificus), photo courtesy of Bob Lane, PhD.

By using a real-time PCR specifically designed to detect R. tillamookensis DNA, the researchers analyzed isolated DNA samples from 348 host-seeking I. pacificus nymphal ticks that were gathered from nine sites within five California counties as well as samples from 916 I. pacificus adult ticks from 24 sites located in 13 counties. The DNA of R. tillamookensis was identified in 10 nymphs (2.9%) and 17 adults (1.9%) that were sourced from 11 northern California counties. According to the study, site-specific infection rates fluctuated considerably, and infection frequencies were consistently low when grouped by stage, sex, habitat type, or geographical region.

The scientists cultivated four novel isolates of R. tillamookensis in Vero E6 cells from adult ticks found in Alameda, Nevada, and Yolo counties. Past isolate strains that had been previously serotyped as ‘Tillamook-like’ and placed in long-term storage over four decades ago were restored and later, using molecular methods were confirmed to be isolates of R. tillamookensis.

Further investigation is needed to better understand the possible impact that R. tillamookensis may have on public health.

Read the study in Journal of Medical Entomology.

Read more about other Rickettsia species.