Serologic and virologic survey for evidence of infection with velogenic Newcastle disease virus in Chinese duck farms.

A serologic and virologic survey was performed to determine the prevalence and distribution of Newcastle disease virus (NDV) infection in Chinese duck flocks. NDV infection was detected in nine of the 12 sampled farms throughout the two geographic regions covered by the survey. The percentage antibody positivity among the 406 serum samples was 35.7%. Three velogenic NDVs were obtained from different duck flocks identified by hemagglutination and hemagglutination-inhibition tests, a pathogenicity test, and reverse transcription-polymerase chain reaction on the fusion (F) genes. Phylogenetic analysis revealed that all three isolates clustered with the class II viruses; two were phylogenetically close to genotype VII NDVs, and the other was more closely related to genotype IX NDVs. These findings suggest that NDV infections were prevalent, and at least two distinct virulent genotypes may be responsible for recent epidemics in Chinese duck flocks.