| Avian influenza virus(AIV)is A virus isolated from the bird host and adapted to host It has unique evolutionary and adaptive capabilities,and also has the ability to replicate and spread in new hosts.Most AIV causes little or no disease in waterfowl,but outbreaks in poultry are often accompanied by high mortality and pose a significant threat to the poultry industry and human health.Therefore,it is of great significance to carry out research on AIV monitoring and regularly of epidemic.In this study,epidemiological investigations were carried out in Jiangsu Yancheng Wetland National Nature Reserve,Nanjing Hongshan Forest Zoo and some live poultry trading markets in Jiangsu province in 2018-2019.A total of 2,474 samples were collected,and 2 strains of H3 subtype and 18 strains of H9N2 subtype AIV were isolated.It was found that the total positive rate of AIV was 5.13%and that of wild animals was 2.22%.The market sample positive rate was 12.91%.The positive samples of AIV were identified,and it was found that the detection rates of H5 and H9 subtypes of avian influenza virus were high,accounting for 33.07%and 26.77%of AIV positive samples,respectively,and there was a certain degree of mixed infection of H5,H7 and H9 subtypes influenza virus.AIV prevalence in two demonstration poultry farms was monitored,and 1176 samples were detected,with a positive AIV rate of 1.19%.The average HI titer of H5,H7,H9 and NDV in 2601 serum samples from the poultry farm can reach more than 27 and is relatively stable.Whole genome sequencing was performed on H3 subtype,and it was found that all the internal genes except M and NA belonged to the Eurasian lineage.M,NA genes underwent complex recombination:the NA genes of B1278/H3N2 and the M genes of B1180/H3N8 were recombined with H9N2 subtype influenza viruses respectively,and the NA genes of B1180/H3N8 were recombined with the North American N8 lineage,which may be the result of virus transmission variation in wild birds during migration.Amino acid sequence analysis showed that the cleavage sites of HA protein were KQTRGIF,which was consistent with the characteristics of low pathogenicity avian influenza virus.Among the HA protein receptor binding sites,no obvious human receptor binding sites were found,indicating that the strain was still more inclined to bind to poultry cells.Some sites of PB2,Ml and NS1 were mutated,which enhanced the pathogenicity and virulence to mice.M2 protein has a mutation of I27V,which reduces the sensitivity of the influenza drugs rimantadine and amantadine.Compared with human influenza H3N2 subtype and some H3 subtype viruses,the HA gene has fewer glycosylated sites and is highly conserved.The amplification,genetic evolution and molecular characteristics of HA and NA genes of 18 strains of H9N2 subtype virus were analyzed.Study found that all the HA genes were clustered in Y280 lineage and NA genes were in BJ/1/94 lineage.All H9N2 subtype AIV were closely related to the H9 viruses isolated from Jiangxi,Jiangsu,Shanghai and other regions of China in recent years.It is far from the H9N2 virus found in earlier years,suggesting that HA and NA genes of H9 subtype have been mutated,which should be paid attention to.The cleavage sites between HA1 and HA2 proteins of all H9N2 subtype AIV strains were PSRSSRGLF,which could be judged as low pathogenicity avian influenza.The amino acid sequence at the HA protein receptor binding site was highly conserved,which was the same as that at the same location of most H9N2 viruses,but the 198 site of HA protein in some H9N2 isolates was mutated.The 226 and 228 sites of its HA protein are Q and G,so that the strain still tends to bind to ?-2,3 sialic acid receptor of avian origin.NA protein sequence analysis showed that the virus was still very sensitive to NA inhibitors.This study provides data support for the epidemiological investigation of avian influenza virus in Jiangsu province and is of great significance for the evolutionary analysis of avian influenza virus and disease prevention and control. |
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