In April, 1973, an acute disease with a high rate of mortality appeared in a flock of 233 ducks and geese at a private game farm. Most of the flock (220) were black ducks (Anas rubripes) and mortality was restricted to them. In May, the remaining live birds were placed in isolation but mortality continued in black ducks and occurred in other species. The overall rate of mortality for black ducks was 93% and the case fatality rate was 97%. No hemorrhaging from either the bill or vent was observed. The most commonly observed gross lesions were extensive fibrino-necrotic plaques covering the mucosal surface of the esophagus, posterior colon and cloaca. Petechial and ecchymotic hemorrhages on visceral organs, particularly the heart, were also common. Virus isolation was attempted from tissues of three black ducks. Duck plague virus was isolated from liver, kidney, spleen and intestine of each. Sixteen black ducks survived the outbreak. Seven of these birds had significant levels of neutralizing antibody to duck plague virus.
Diagnostician APHIS, USDA at the Wisconsin Central Animal Health Laboratory, 6101 Mineral Point Rd., Madison, Wisconsin 53705, USA.
Diagnostic Virology, Veterinary Services Diagnostic Laboratories, APHIS, USDA National Animal Health Laboratory, P.O. Box 70, Ames, Iowa 50010, USA.
Department of Veterinary Science, University of Wisconsin, Madison, Wisconsin 53706, USA.