Heterogeneities Of Pathogenicity And Antigenicity In Relation To The Genetic Variation Of F And HN Genes In Prevailed Newcastle Disease Viruses

Newcastle disease is one of the most serious infectious diseases caused by Newcastle disease virus (NDV) in poultry. The virus is classified as a member of the Rubulavirus genus sub-family Paramyxovirinae in the family Paramyxoviridae, belonging to Mononegavirales and is designated avian paramyxovirus-1 (APMV-1). It causes high morbidity and mortality in non-immunized chickens even in some immunized chickens population with respiratory tract infection as well as egg drop. ND has been regarded as the most devastating disease in poultry industry for more than 60 years. Many scholars tried to discover the molecular variation trend of NDV, and a lot of data on molecular epidemiology have been reported in the past ten years, but the relation between the biological properties and genetic variations, especially the relationship between the genetic and antigenic evolution of the fusion protein (F) gene and hemagglutinin-neuraminidase (HN) is still not clear.F genes and HN genes of 30 NDV field isolates were cloned and sequenced in present study, and the pathogenicity and antigenicity of these isolates were evaluated. Then the heterogeneity of pathogenicity and antigenicity in relation to the genetic variation of F and HN genes in prevailed Newcastle disease viruses was analyzed. The study was focused on the following areas:1. Isolation, identification and plaque-purification of 30 NDV field isolates.Thirty NDV field isolates were isolated from the poultry populations in Shandong and Jiangsu province between 1996～2005. The viruses were identified by HI test using NDV and AIV (H5 and H9) positive serum. At the same time, twenty isolates were purified by plaque-purification test.2. Comparisons of pathogenicity by different NDV strainsBased on the value of MDT, ICPI and IVPI of the 30 NDV field isolates, twenty-eight field isolates were designated as velogenic isolates, one was mesogenic and the pathogenicity of the remanent one was not sure. Twenty NDV isolates were purified by plaque. The pathogenicity tests were repeated twice and the results were identical before and after plaque purification except for two NDV isolate, The ICPI value of SBZ02 decreased, while that of the other isolate SY03 increased after several passages in embryos. This suggested there were other viruses mixed with these two isolates.3. Antigenic variation of NDV field isolatesSeventeen NDV isolates purified by plaque were selected in this study. Positive serum of every NDV isolate was prepared in SPF chicken. The HI and cross-neutralization tests were...