Expanding Distribution of Pacific Coast Tick and Rickettsia Pathogens

Journal of Medical Entomology (Paddock, CD, et al.) 02.26.2024, published, “Rickettsia species identified in adult, host-seeking Dermacentor occidentalis (Acari: Ixodidae) from Baja California, Mexico, and Oregon and Washington, United States.” In this study, researchers collected and tested 1,367 host-seeking, adult D. occidentalis (Pacific Coast ticks), between 2015 – 2022 in Baja California, Mexico, and Oregon and Washington. This is the first survey for rickettsiae in Pacific Coast ticks from these regions.

Genus and species-specific assays were used for detection of spotted fever group rickettsiae. Though DNA of Rickettsia 364D, R. bellii, and R. tillamookensis were not detected in these regions, DNA of R. rhipicephali was detected in ticks collected in Baja California and southwestern Oregon. All ompA sequences of R. rhipichephali from ticks in southwestern Oregon were represented by a single genotype. Also detected was the first report of Rickettsia endosymbiont of I. pacificus in Pacific Coast ticks collected from southwestern Oregon and Washington. 

Increased surveillance efforts have shown expanded geographical distributions for multiple hard tick species of medical importance in the US. Historical records and more recent citizen science research show that distributions of Pacific Coast ticks in Oregon and Washington are more vast than previously understood.

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