| H9N2 subtype avian influenza virus is a kind of low pathogenic avian influenza virus,which has the characteristics of long epidemic time,wide spread range and many types of infected hosts.Since China first isolated the virus in 1992,it has spread to most parts of the country in decades.The H9N2 subtype avian influenza virus mainly harms all kinds of poultry.The number of poultry breeding in our country is huge.The prevalence of H9N2 in China has caused serious economic loss to the poultry breeding industry.Not only that,but H9N2 has also been proven to have the ability to infect humans,which poses a huge hidden danger to human and public health.It is worth nothing that the H5N1 and H7N9 subtype avian influenza viruses are closely related to the spread of H9N2.Studies have shown that six internal fragments of H7N9 are derived from H9N2,which plays a key role in the emergence of new subtypes and strains as gene donors during recombination.Trial 1 Epidemiological survey of H9N2 subtype avian influenza in some regions of china in 2018Two epidemiological surveys were conducted in the first half of the year(Mar.-May)and the second half of 2018(Oct.-Dec.).In the first half of the year,4792 samples of throat/cloaca swabs were randomly collected from 67 sites in 11 provinces of China,and 1208 positive samples of H9N2 subtypes were detected.The total positive rate of samples was 25.21%(1208/4792).The positive rate of sites is 80.60%(54/67).In addition,1090 chicken positive samples,86 duck positive samples,2 goose positive samples and 30 pigeon positive samples were detected.The positive rates of each host sample were 29.18%(1090/3736),12.23%(86/703),1.53%(2/131)and 13.51%(30/222).In the second half of 2018,995 positive samples of H9N2 subtypes were detected,the total positive rate of the samples was 24.14%(995/4122).51 sites were positive in 68 sites,the total positive rate of the sites was 75.00%(51/68).In addition,813 chicken positive samples,100 duck positive samples,6 goose positive samples,and 76 pigeon positive samples were detected.The positive rates of each host sample were 25.89%(813/3140),16.23%(100/616),10.34%(6/58)and 25.50%(76/298).Avian influenza virus was not detected in 220 poultry purchased from 13 provinces(municipalities)through Taobao net.Trial 2 Epidemiological statistical analysis of H9N2 subtype avian influenza from 2008 to 2018This paper makes statistics on the epidemiological results of H9N2 subtype avian influenza viruses from 2008 to 2018.In the past ten years,samples from Shanghai,Jiangsu,Jiangxi,Hubei,Guangdong,Guangxi,Heilongjiang,Yunnan,and Tibet were collected from various farms and markets.The pharyngeal and anal swab samples,serum samples,environmental samples of the slaughterhouses and the poultry farms were sampled 22 times,and the total number of samples was 122,611.The results are as follow:? From the first half of 2008 to the second half of 2018,the overall positive rate of H9N2 subtype avian influenza increased from 0.47%to 24.14%,and the overall sample positive rate increased by 51.36 times.It shows that the infection of H9N2 is generally on the rise from 2008 to 2018.Correspondingly,the province's positive rate has increased by 3.6 times from 25%in 2008 to 90%in 2018.In addition,the total field positive rate has increased from 3.33%in 2008 to 75%in 2018.It has increased by 22.52 times.It can be said that the proliferation rate of H9N2 subtype avian influenza in China has been very rapid in the past ten years.?By analyzing the distribution of positive rate of field,we found that almost all the sites of poultry farming in our country exist H9N2 subtypes avian influenza.It is worth noting that the positive rate of live bird wholesale market and live bird retail market is significantly higher than other sites,and in recent years there is a gradual increase trend,the positive rate of samples in the retail market before 2016 was higher,and the positive rate of the wholesale market after 2016 had a significant increase;? In this study,we analyzed the distribution of the positive rate of H9N2 subtype avian influenza virus in each host,and found that the positive rate of chicken in all hosts was at a high level all the year round.In addition,the infection rate of waterfowl and pigeons has a large increase trend after 2017,and in the second half of 2018,it reached the highest level in history.Trial 3 Genetic evolution analysis of H9 gene in 2008-2018A total of 6771 H9 gene sequences were obtained in this study.The sequences were compared and genetically evolved by MEGA.The results showed that 129 branches of h9.4.2.6,6610 branches of h9.4.2.5,9 branches of h9.4.2.4 and 20 branches of h9.4.1.2 were detected between 2008 and 2018.In the branch of h9.4.2.5,chickens,ducks,geese,pigeons and wild birds are infected,among which chickens have the highest infection rate,accounting for 88.31%of the total(5837/6610),indicating h9.4.2.5 branches may have a pharyngeal preference for chickens.Over time,the H9N2 virus is constantly evolving.The development trend of the phylogenetic tree indicates that the strains isolated in 2013-2018 have a large difference compared with the isolates from 2008 to 2012,which means that in recent years although the popular branch has not changed,there are still recombination and mutations between the internal strains.As the genetic distance increases,new branches are likely to replace h9.4.2.5 in the future. |
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