Surveillance for tick-borne pathogens on US military installations in California and Alaska

The risk of tick-borne infections on US military installations is not well known, primarily due to limited surveillance. This information gap hinders accurate disease risk assessment, prevention efforts, and timely diagnosis. Service members are at risk due to frequent exposure to field training environments. We seek to determine accurate risk levels on US military installations, with California and Alaska as current areas of interest. The main objectives of the study were to: i) conduct tick surveillance on select military installations, ii) identify tick species and screen for pathogens, and iii) advise US forces and the public in and around the surveilled installations. The study sites included four installations in California and one in Anchorage, Alaska. In California, ticks were collected using standard tick drags or removed from deer. In Alaska, ticks were removed from live-trapped small mammals. Our results show an abundance of three Dermacentor species in the surveilled installations in California, and Ixodes angustus on the base in Anchorage. In total, 894 ticks were collected from four installations in California and 44 ticks collected from one installation in Anchorage. Ticks were screened for multiple pathogens using real-time PCR. Rickettsia positive samples were subjected to Sanger sequencing for species confirmation. Ticks from California installations were positive for Rickettsia species, including R. rhipicephali, R. monacensis and R. montanensis. Samples from Anchorage tested negative for Anaplasma phagocytophilum, Powassan virus and Borrelia burgdorferi. We discuss the ecological and health implications of our results and provide recommendations for force health protection.