Genetic, pathogenic and antigenic diversity of Newcastle disease viruses in Shandong Province, China.

Thirty-one Newcastle disease viruses (NDVs) isolated from domestic and wild birds in Shandong Province, China (2006-2014) were characterized genetically, pathogenically and antigenically. Phylogenetic analysis classified the viruses into a single genotype under Class I, and four genotypes under Class II. The nineteen viruses classified in genotype VII of Class II were velogenic, while the other viruses were either mesogenic or lentogenic to chickens. Some NDV isolates (17/23) showed no neutralizing reactivity with a monoclonal antibody developed against the HN protein of the LaSota strain, reflecting the mutation at the related antigenic epitope. When challenged with two genotype VII NDV isolates, LaSota-vaccinated SPF chickens were prevented from disease development, but virus shedding was detected for at least 5 days post challenge. Circulation of the same NDV isolate for up to 13 years suggested the role of an environmental reservoir in NDV perpetuation, and reinforced the importance of strict biosecurity measures in addition to vaccination for disease control.