Epidemiology And Pathogenicity On Muscovy Duck Of H9N2 Subtype Avian Influenza Virus

H9N2 subtype avian influenza virus(AIV) has been isolating all over the world from kinds of birds and poultry, as well as human sometimes, so it is quite important to study H9N2 subtype AIV in the economy of poultry enterprise and public health. H9N2 subtype AIV is one of the most common pathogen in aviculture, and had isolated in different area in China since H9N2 subtype avian influenza was first reported epidemic in China in 1994. With the rapid development of duck industry in the recent years, infection of H9N2 subtype AIV in duck has constantly emerging。To grasp the latest variation of H9N2 subtype AIV and the situation of Muscovy duck infected with H9N2 subtype AIV in the most area of South China, we have investigated epidemiology of H9N2 by isolation, identification and sequence analysis and serological methods. In this study, 24 H9N2 subtype AIV strains were isolated, including 20 strains from chicken and 4 strains from duck. The results of sequence analysis showed that all of the strains belong to h9.4.2 lineage which was represented by the Y280 strain. The HA gene nucleotide sequence identity among the 24 strains was from 94.0%-99.9%, and the HA gene nucleotide sequence identity between the 24 strains and vaccine strains, SS94 strain、F98 strain and 6/96 strain, was 89.4%-90.7%,88.1%-89.2%和 88.6%-90.0%, respectively. The common form about the cleavage point of HA protein is PSRSSR↓GLF, complying with the characteristics of lowly pathogenic avian influenza virus(LPAIV). The result of serological investigation indicated that the positive rate was ranged from 1.51% to 5.54%, the average of it is 3.2%, and the highest is 5.54% in 2015.6, and the lowest is 1.51% in 2015.7.Make research of the pathogenicity of H9N2 subtype AIV on young Muscovy duck and egg Muscovy duck by using A/Chicken/Guangdong/2015/Ch1 strain isolated from chicken, A/Duck/Shandong/2015/SDQ strain and A/Duck/Shandong/2015/SD5 strain isolated from duck. The result showed that the yong Muscovy duck could be infected with the H9N2 subtype AIV strains isolated form diffenerent host, and there have difference in the elimination of virus. The lung have damage in different degrees infected artificial with H9N2 subtype AIV by diverse route, and the intravenous injection group of duck more severe lung damage relative to the other three test group. Muscovy duck infected with H9N2 subtype AIV have changes in the levels of immune related cytokine m RNA expression, it showed that infected with H9N2 subtype AIV could affect the young Muscovy ducks immune balance. And the laying rate of egg Muscovy ducks was keep steady after being infected with H9N2 subtype AIV, it indicates that a single H9N2 infections does not make egg production of egg Muscovy ducks performance degradation.In addition, the mortaliy of the ducks infected with H9N2 subtype AIV and Riemerella anatipestifer could be increased compered with the ducks only infected with Riemerella anatipestifer in the early time of infection, suggestting that H9N2 AIV can cause the decline of young muscovy ducks resistance. After H9N2 subtype AIV infections, the antibody level has dropped, suggests H9N2 AIV infections can affect the antibody levels of ducks inoculated with muscovy duck parvovirus and reovirusis live attenuated vaccine respectively. The above analysis shows that H9N2 AIV infection can cause the young Muscovy ducks immunosuppression, affect the resistance to pathogens and vaccine immune effect of young muscovy ducks.