Investigation of and Response to 2 Plague Cases, Yosemite National Park, California, USA, 2015

In August 2015, two cases of plague caused by Yersinia pestis were confirmed in visitors to Yosemite National Park, California. One patient presented with septicemic plague while the other had bubonic plague. Environmental investigations pinpointed distinct exposure locations for each case and detected evidence of an ongoing epizootic in the park. Genetic analysis using whole-genome multilocus sequence typing revealed that at least two separate strains of Y. pestis were circulating among rodent hosts and flea vectors, indicating multiple transmission chains. Public health interventions, including education campaigns and targeted insecticide applications to control fleas, likely mitigated further risk to park visitors and staff.

Danforth, M., Novak, M., Petersen, J., Mead, P., Kingry, L., Weinburke, M., Buttke, D., Hacker, G., Tucker, J., Niemela, M., Jackson, B., Padgett, K., Liebman, K., Vugia, D., & Kramer, V. (2016). Investigation of and Response to 2 Plague Cases, Yosemite National Park, California, USA, 2015. Emerging Infectious Diseases, 22(12). https://doi.org/10.3201/eid2212.160560