There is a risk of the transmission of various vector-borne illnesses in Yosemite National Park (YOSE), including hantavirus pulmonary syndrome (HPS), plague, Lyme disease, and soft tick relapsing fever (STRF). Ongoing surveillance and assessment help to understand spatial and temporal trends in human disease risk and guide public education efforts. Under this permit, the primary vertebrate surveillance efforts focused on rodent reservoirs of these diseases. Deer mice (Peromyscus maniculatus) were trapped to assess their relative abundance and tested to estimate the prevalence of Sin Nombre virus (SNV) antibodies, as they are the primary reservoir species of SNV, the causative agent of HPS in California. Chipmunks and ground squirrels were also trapped and tested for the presence of Yersinia pestis antibodies or Y. pestis bacteria, the causative agent of plague. The invertebrate surveillance efforts included flea collections from trapped rodents for plague testing, collecting soft ticks and kissing bugs in and around structures, and flagging vegetation along trails for Ixodid ticks, primarily to collect Ixodes pacificus and Dermacentor species. As part of an on-going cooperative agreement between YOSE and Public Health Foundation Enterprises (doing business as Heluna Health), the primary objectives for 2025 included continued evaluations of SNV and Y. pestis seroprevalence in rodent populations in Yosemite Valley, Tuolumne Meadows, and other select areas of the park. Estimates of rodent abundance and pathogen seroprevalence, coupled with facility evaluations to assess rodent activity in developed areas, help to estimate the hantavirus and plague exposure risks to visitors and NPS staff. These results, considered along with historical surveillance data, will help to further refine disease prevention recommendations. A summary of findings including observations, laboratory test results, and disease prevention recommendations are provided to the NPS annually. In addition to hantavirus and plague surveillance, surveillance for arthropod vectors of other diseases such as STRF, Chagas disease, and Lyme disease may be conducted throughout the park and NPS properties in El Portal.

In Review