Epizootiology of skunk rabies in North America

Public health surveillance data from the United States and Canada (1961 to 1982) were analyzed to determine if consistent temporal and spatial patterns in skunk rabies could be identified. Enzootic/epizootic rabies was recognized in 18 states (enzootic states) based on the criteria of greater than or equal to 20 yr of reported skunk rabies and at least 1 yr with a minimum of 50 reported rabid skunks. In other wildlife species, epizootics have been demonstrated to expand along a wave-like front. We hypothesized: if skunk rabies behaved in a similar fashion, states reporting rabid skunks would change over time. No such change was noted. During epizootics the number of counties reporting increased but not the number of states. Within Illinois certain counties were demonstrated to have persistent rabies histories and likely served as enzootic foci. Enzootic states combined prevalence indicated a 6 to 8 yr cycle for epizootics. Data on monthly percent rabies positive (number rabid/total number tested) were available from six states and Canada. Mean distributions were bimodal with winter and spring peaks. The patterns identified for skunk rabies differ from those of other major wildlife vectors and have significance for potential vaccination control regimes.