Research On Genetic Evolution Analysis And Pathogenicity Of 9 Strains Of NDV From Different Origins

Newcastle disease?ND?is an infectious disease caused by Newcastle disease virus?NDV?.In this study,the serological investigation of ND was carried out in Hebei province.The genetic variation analysis of 9 strains of NDV isolated and identified from Hebei province and surrounding areas.Finally,3 strains of NDV were experiment for chicken pathogenicity.It could provide an important theoretical basis for the prevention and control of ND in China,and also lay a foundation for further study of cross-species transmission and molecular biological mechanism of NDV.In this study,a total of 2,941 serum samples collected from Hebei province from 2015to 2018 were investigated by NDV.The results showed that there were differences in the ND antibody levels of immunized poultry groups?chickens,racing pigeons and mannikin?,the ND antibody level of chickens was the highest,that of racing pigeons was poor,and that of mannikin was negative.Some serum samples of non-immune ducks were ND positive,which indicated that NDV wild strain infection existed in the duck flocks investigated.In this study,9 strains of NDV were isolated and identified from the samples collected from Hebei province and surrounding areas,which named by HB/1/08/Os strain,HB/1/15/Br strain,BJ/1/15/Ck strain,TJ/1/15/Pi strain,HB/1/16/ck strain,HB/2/16/ck strain,HB/1/16/Pa strain,HB/1/15/Go strain,and HB/1/16/Dk strain.The results of MDT and ICPI showed that 7 NDVs including HB/1/08/Os strain,HB/1/15/Br strain,BJ/1/15/Ck strain,TJ/1/15/Pi strain,HB/1/16/Ck strain,HB/2/16/Ck strain and HB/1/16/Pa,were belonged to virulent strains.While HB/1/15/Go strain and HB/1/16/Dk strain were both avirulent strains.The results of genome sequence analysis of 9 NDVs indicated that the full length of the NDV genome of the 7 virulent strains was 15192 nt,and the HN gene ORF length of HB/1/16/Ck strains was 1749 nt,encoding 582 amino acids,while the HN gene ORF length of the other 6 strains was 1716 nt,encoding 571 amino acids.The length of the full genome of the two avirulent NDVs was 15186 nt,and the ORF length of the HN genes was 1734 nt,encoding 577 amino acids.Homology analysis showed that the identity of nucleotide and amino acid between 5 NDVs?HB/1/08/Os,HB/1/15/Br,BJ/1/15/Ck,HB/1/16/Ck and HB/2/16/Ck?were 97.7%⁹9.1%and 97.1%⁹8.8%,respectively.The homology of nucleotide and amino acid between TJ/1/15/Pi strain and HB/1/16/Pa strain were 99.1%and 91.6%,respectively.The homology of nucleotide and amino acid between HB/1/15/Go and HB/1/16/Dk strains were 99.9%and 99.6%,respectively.The results of genetic evolution analysis demonstrated the 9 strains of NDV were belonged to Class?.HB/1/08/Os strain,HB/1/15/Br strain,BJ/1/15/Ck strain,HB/1/16/Ck strain and HB/2/16/Ck strain all belonged to the gene?d subtype.TJ/1/15/Pi strain and HB/1/16/Pa strain belonged to the gene?b subtype.And HB/1/15/Go strain and HB/1/16/Dk strain belonged to the gene?type.The cleavage sites were all ¹¹²RRQKRF¹1717 in the F gene of the7 virulent strains,and the cleavage sites were all ¹¹²GRQGRL¹¹⁷ in the F gene of the 2avirulent strains.The comparison results of amino acid of HN gene showed that E347K mutation was found in 3 NDV strains of chicken origin?BJ/1/15/Ck,HB/1/16/Ck and HB/2/16/Ck?.The results of pathogenicity experiment showed that the chickens displayed clinical symptoms,autopsy lesions and histopathological changes of typical ND,which inoculated with HB/2/16/Ck strain and TJ/1/15/Pi strain,respectively.It showed that the 2 NDVs mentioned above were highly pathogenic to non-immunized chickens.However,the HB/1/16/Dk strain was less pathogenic to non-immune chickens.The results of this study showed that the avian species infected with NDV were more from Hebei in recent years.The genotypes of 9 strains of NDV were composed of gene?type,?b subtype and gene?d subtype,and the last genotype was dominant.It has brought great threat to the poultry industry in Hebei province,should attract the attention of relevant personnel.