U.S. Department of Agriculture: Animal and Plant Health Inspection Service


Date of this Version



Proceedings of the 14th WDM Conference (2012).


Studying the lower Shoshone River Basin’s (SRB) striped skunk (Mephitis mephitis) rabies 6-year epizootic in northwestern Wyoming has produced four didactic lessons. First, physiographic changes by settlers circa 1900 affected its zoogeography by creating a canal system for irrigating crops originating at Buffalo Bill Reservoir (BBR). The resulting landscape changes increased agricultural lands and skunk habitat eightfold between the valley’s steep gravel benches. The valley was historically free of skunk rabies until the epizootic’s index case in August 1988. Second, human intervention began when the Bighorn County Predator Board (BCPB) proactively implemented rabies trapping surveillance and depopulation programs in 1989. The epizootic’s second case occurred in February 1989. From 1990–1993, the U.S. Department of Agriculture, Animal and Plant Health Inspection Service, Wildlife Services (WS) Wyoming office continued these programs. The epizootic ended in 1993 with over 200 rabid animals diagnosed by the Wyoming State Veterinary Laboratory (WSVL) from about 1,000 skunks tested. Cooperator agreements began in January 1989 and continued throughout the epizootic for trapping and shooting of potential vectors. Third, WS National Wildlife Research Center (NWRC) analyzed the epizootic movements using monthly mean movements and standardized ellipsoids. These analyses demonstrated that rabies dispersed radially from the index case until it reached the Shoshone River. From there, the epizootic spread downstream until stopped by Bighorn Lake (BL) in 1989 and upstream until stopped by BBR in 1992. Fourth, descriptive multivariate movement maps (MMMs) of the epizootic were analogous to fluid wave characteristics describing a swell moving along the surface of a liquid as the “leading edge” and “crest.” All rabid animal locations were derived from the first use of global positioning system (GPS) in investigating wildlife disease. These lessons learned should assist others to better understand skunk rabies epizootics.