BACKGROUND: In May 2015, the Idaho Department of Fish and Game (IDFG) received reports of Piute ground squirrel (Urocitellus mollis) die-offs in the Snake River Birds of Prey National Conservation Area (SRBPNCA) in southwestern Idaho. Ground squirrel carcasses submitted to the Centers for Disease Control and Prevention (CDC) tested positive for Yersinia pestisby direct fluorescent antibody (DFA), real-time polymerase chain reaction (RT-PCR), and culture. Because SRBPNCA is used for scientific study, military training, and recreation a multiagency response to prevent plague cases in humans and pets ensued.
METHODS: We estimated the geographic area of concern (AOC) within and surrounding the SRBPNCA based on mortality surveys and reports, laboratory findings, and likely U. mollis habitat. We informed the public about the apparent plague epizootic through press releases, social media, agency websites, mailers to homes in high-risk settings, and warning signs posted at AOC access points. We developed and posted an interactive map on multiple agency websites, allowing the public to ascertain their proximity to the AOC. We developed a web-based wildlife mortality event reporting system. We used health alerts to stimulate passive surveillance among health care providers and veterinarians for suspected plague cases. We evaluated potential veterinary and household exposures and provided monitoring and prophylaxis guidance. The Idaho Bureau of Laboratories (IBL) tested human and veterinary specimens for Y. pestis by DFA, rtPCR, and culture. Wildlife specimens were tested by IBL, CDC, and United States Geological Survey (USGS).
RESULTS: Two persons, both reporting rodent exposure and illness, tested negative for plague by IBL. Of 18 pets (canine [12], feline [6]) tested by IBL, 17 (94.4%) tested negative; one canine tested presumptive positive for Y. pestis by RT-PCR. Prophylaxis was used for canine-associated high-risk occupational and household exposures. IDFG received 80 rodent mortality reports from nine counties. CDC confirmed Y. pestis in three of four (75%) ground squirrels submitted from two die-offs in the AOC. IBL tested 23 rodents of six types (17 voles, two woodrats, one each gopher, deer mouse, feral chinchilla, and fox squirrel). Two (11%) of 17 voles tested presumptive positive for plague by DFA; both collected outside the AOC. Voles subsequently submitted to USGS tested negative for plague and tularemia.
CONCLUSIONS: Online tools improved response efficiency by allowing rapid assessment of potential geographic exposure and timely triage of publicly-reported rodent mortality. A multiagency response was effective in preventing transmission of plague from wildlife or pets to humans.