BLUETONGUE IN FREE-RANGING PRONGHORN ANTELOPE (ANTILOCAPRA AMERICANA) IN WYOMING: 1976 AND 1984

At least 3,200 pronghorn (Antilocapra americana) died during a bluetongue (BT) epizootic in eastern Wyoming during late September and early October 1976. In August and September 1984, another BT epizootic occurred in northeastern Wyoming resulting in 300 known pronghorn deaths. In 17 pronghorn examined postmortem, hemorrhages and edema were the most common gross pathologic changes. Microscopic changes included hemorrhage, edema, arterial fibrinoid necrosis, lymphoid depletion in splenic and lymphatic follicles, and neuronal necrosis. Bluetongue virus serotype 17 was isolated from pronghorn in both epizootics. Mortalities ceased with the advent of cool weather in late September and October. Seventy-six of 94 pronghorn killed by hunters during the latter period of the 1976 epizootic, and 14 of 24 pronghorn killed 1 yr later had serologic evidence of exposure to BT virus. The reproductive rate in pronghorn was depressed to 47 fawns per 100 does in August 1977, but returned to 93 fawns per 100 does by 1978. Following the 1984 outbreak, the reproductive rate was similarly depressed, but the cause was confounded by other environmental and range conditions. Deer, mostly mule deer (Odocoileus hemionus), also died during both epizootics of what was presumed to be BT.