Epidemiologic survey of sylvatic plague by serotesting coyote sentinels with enzyme immunoassay

The geographic distribution and areas of high sylvatic plague activity in California were verified by using coyotes (Canis latrans) as sentinel animals. Antibody levels against Yersinia pestis were tested using the enzyme-labelled antibody (ELA) test and the microtiter passive hemagglutination and hemagglutination inhibition. A survey using the ELA test indicated that the overall antibody prevalence among 143 coyotes was 21%. By geographic regions, the highest antibody prevalence was 27% among coyotes from mountain areas on the northern and eastern borders of the state. This was followed by 19% in the central coastal area and 12% in the central valley. Areas with a high prevalence of seropositive coyotes or high antibody levels in individual coyotes matched the four areas of human plague exposures reported in 1977 and 1978. These areas included the central Sierra mountains adjacent to Lake Tahoe, southeastern Kern County, the central coastal area and Scott Valley near the Oregon border. The ELA test appears to be a promising tool for future epidemiologic studies of plague.