Samples of liver, spleen and/or brain were obtained from 370 ducks suspected of having duck plague in 10 provinces in southern Vietnam. Viruses were isolated in duck embryonated eggs from 112 samples (30.3%), with positive samples coming from all provinces. The viruses were confirmed as duck plague virus by antigen capture ELISA. Antigen capture ELISA was also applied to 115 of the original samples. Egg inoculation had a sensitivity of 94.5% and a specificity of 78.3% when compared to antigen capture ELISA. Seven of the new isolates were used to infect ducklings; 2 were avirulent, 3 produced 100% mortality and 2 were of intermediate virulence. None of the isolates killed ducklings that had previously received the locally produced duck plague vaccine. These laboratory studies confirm previous field observations that duck plague is prevalent and an important disease in Vietnam.
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