Pathogenicity of three H9N2 avian influenza viruses of Guangxi sparrow origin to SPF chickens

【Objective】To clarify the pathogenicity of H9N2 avian influenza virus(AIV) of sparrow origin to chickens,which was helpful to understand the role of sparrows in the ecological chain of H9N2 subtype AIV transmission,and it also had important significance for scientific prevention and control of the outbreak of H9N2 subtype AIV.【Method】Three Guangxi H9N2 AIV virus of sparrow origin with HA genes belonging to different evolutionary branches were selected for SPF chicken pathogenicity test. A total of 84 4-week SPF chickens were randomly divided into 4 groups(blank control group and 3 infection groups). In each infection group,16 SPF chickens were infected nasally with 100 μL virus which has been diluted to 10⁶EID₅₀/100 μL,the remaining 5 SPF chickens were placed in each infection group as blank contact group after 24 h of infection. Clinical symptoms and pathological changes of the chickens were observed after infection.Tissues were collected at different time points to make pathological sections,virus titers and distribution in different organs were detected.【Result】Three H9N2 subtype AIV of sparrow origindid not have multiple basic amino acid insertions at the cleavage site of HA protein,showing RSSR↓GLF,which was consistent with the typical molecular characteristics of low pathogenicity AIV(LPAIV).The median infective dose(EID₅₀) of chicken embryos ranged from 10^-6.0/0.2 mL to 10^-6.8/0.2 mL,and median lethal dose(ELD₅₀) ranged from 10^-6.8/0.2 mL to 10^-7.2/0.2 mL. All the three H9N2 AIV could directly infect SPF chickens,and there were some differences in the virus titer and distribution of the virus in different organs. The SPF chickens did not show any obvious clinical symptoms and death,but there was a certain degree of congestion and bleeding in the trachea and lung of the upper respiratory tract,tracheal ciliary detachment,inflammatory lymphocyte infiltration and other changes after infection. The detoxification period of three H9N2 subtype AIV of sparrow origin infected SPF chickens was mainly between 1 d and 7 d,and they could directly infect chickens and detoxify without in vivo adaptation. There were some differences in the replication ability of the three sparrows of H9N2 AIV in the organs of SPF chickens,and they could replicate effectively in the trachea and lung,while no corresponding virus was detected in the liver,brain,pancreas,thymus,heart,cecum tonsil and bursa.【Conclusion】H9N2 subtype AIV of sparrow origin could directly infect chickens and has the potential of horizontal transmission among chickens,suggesting that relevant protective measures should be taken in poultry breeding,transportation and marketing to cut off the transmission routes of AIV between wild birds and poultry,so as to reduce the economic losses caused by avian influenza outbreaks.