Epidemiological Investigations Of H7N9 Subtype Avian Influenza In 4 Provinces Of China In 2017

In order to fully understand the infection situation of H7N9 avian influenza in the key areas,analyzing the distribution patterns in different hosts,different regions and regions,so that it could conduct targeted prevention and control to H7N9 avian influenza virus.In this study,epidemiological sampling was conducted in 123 sites in 4 major provinces in the southeast of China in mid-February 2017.A total of 3786 samples of cloacal and throat swabs and 3033 serum samples were collected.After the detection and epidemiological analysis of the pharynx/anal swab samples,the following inferences are obtained:?Compared with the monitoring data in the same period and the same area in the past year,the total positive rate of the H7N9 subtype avian influenza virus reached 2.48%,which is much higher than the previous monitoring results,and the infection situation is on the rise.?The analysis results show that the live poultry trading places is still the main detection area type of positive samples,but it is different from the past that the infected area has obvious tendency to expand the scope of the detection,covering the slaughterhouses,farms,poultry wholesale market,live poultry retail market,and many other areas.The scope of infection had obvious diversification;The positive rate of the total sample virus reached to 2.48%,far higher than the previous monitoring results and the infection is still on the rise;?From the analysis of the infection of the host range,H7N9 subtype avian influenza virus in chicken positive rate was 2.51%,which remained at a high level,while the positive rate of duck samples reached 1.89%,significantly higher than previous monitoring results,and other poultry samples are also detected positive samples,which suggesting that infected poultry gradually is expanding.After the blood coagulation inhibition test(HI)to determine the level of antibody of the 3033 serum samples collected at the same time.The following conclusions were obtained:?99 HI antibody positive samples(HI titer?4 log2)were detected,the total positive rate is 3.26%,The level of antibody was relative low.?The 99 positive samples(HI titer?4 log2)were mainly from the large live poultry markets and scale breeding farms,while slaughterhouses and individual farmers did not detect antibody positive sample,which suggesting that H7N9 subtype avian influenza virus main contaminated the large live poultry markets and scale breeding farms in these 4 province,same with the pathogen detection result of pharynx/anal swabs.Since the H7N9 subtype of avian influenza virus was found in Shanghai and Anhui at the end of March 2013,it has appeared in various provinces and cities throughout the our country.In the autumn of 2017,the state issued a comprehensive policy indication of H7N9 subtype avian influenza vaccination,in order to control the epidemic situation.But,due to the mutation and evolution of the virus itself,the protection effect of the existing vaccine is difficult to predict,so it is very important to understand the distribution and variation of the virus.In the later stage of the experiment,we measured the gene sequence of 94 positive sample strains.According to the survey of the background information and compared the gene order with vaccine strains,we got the following conclusions after genetic evolution analysis:?94 strains of H7N9 subtype avian influenza virus were detected,and the amino acid sequences at the cleavage site of HA gene were all“—PEIPKGR/GLF—",which accords with the molecular biological characteristics of low pathogenic avian influenza virus.?Comparing the gene sequence of 94 strains of H7N9 subtype avian influenza virus we have got with the vaccine strains were and making evolutionary trees,we can find that strains separated form Fujian,Anhui,Henan and Shanghai in 2017 are relatively close with vaccine strains in genetic lineage,and all of them belong to the h7.2 branch of the Eurasian genealogy,while there is no obvious variation.The current vaccine has a certain protective effect to the virus strains prevalent in the above areas.