Epidemiology Investigation Of H5 Subtype Avian Influenza Viruses Isolated In Parts Of China Between2014 And 2015

Since 1996,the H5 subtype of highly pathogenic AIV was isolated from chicken in Chinese mainland for the first time.After that,H5 AIV began to spread widely in poultry in our country.H5 subtype AIV can break species barriers to infect other mammals,including humans through genetic recombination.,In 1997 the first case of human infection with the H5N1 avian influenza appeared in Hong Kong which caused the death,people started to pay high attention to H5 AIV.In order to learn about the prevalence of H5 subtype AIV in eastern part of China between Nov.2014 and Oct.2015,we collected 228 samples from clinical cases in different provinces and 3089 samples from live bird markets?LBMs?in Guangdong.53 strains of H5 subtype AIV have been isolated from 228 samples which were isolated from clinical cases.The isolated rate is 23.2%.There are 69.8% strains coming from waterfowl.99 strains of H5 subtype AIV have been isolated byembryonated eggs in LBMs samples.The isolated rate is 3.2%.There are 55.6% of H5 subtype AIVs coming form waterfowl,which proves that the ducks are the main host for H5 subtype AIVs in Guangdong LBMs.It proves that the waterfowl is the most important host for H5 subtype.HA and NA gene of 29 strains of H5 subtype AIV from LBMs and 53 strains of H5 subtype AIV from clinical cases were identified by gene sequencing.69.8% of H5 subtype AIV from clinical cases are H5N6 and 82.8% of H5 subtype AIV from LBMs are H5N6.It proves that the most popular H5 subtype AVI in the area where we collected samples is H5N6.The HA gene evolution was analyzed by MEGA5.2.The result showed that 96.6% strains of H5 subtype AIV from LBMs and 77.4% strains of H5 subtype AIV from clinical cases had HA gene in Clade2.3.4.4.Other strains were in Clade2.3.2.1.It proves that the strains of Clade2.3.4.4 are the most popular strains in the area where we studied.Through analyzing the HA protein of the 82 strains of H5 AIV,we found that all of the strains had multiple consecutive basic amino acid in cracking sites and 11 strains had S137 A,T192I double mutation which could enhance receptor binding capacity of AIV on sialic acid alpha 2-6 galactose?SA alpha 2-6 Gal?.One of these strains was separated from the samples of LBMs.Four representative strains of H5 subtype AIV were selected for pathogenicity examination to understand the pathogenicity of H5 subtype AIV on different animals.SPF chickens and BALB/c mice were inoculated intranasally with 105EID₅₀ and 106EID₅₀ of representative strains which are highly pathogenic avian influenza virus?HPAIV?.The results showed that all the strains could infect and kill the mice.The strains which have S137 A,T192I double mutation in HA protein have higher pathogenicity and we didn't find the evidence to prove that the NA subtype could influence the pathogenicity.Some of the AIVs which were separated from LBMs also have S137 A,T192I double mutation in HA protein,so the H5 AIV have a chance to infect humans who are connected with LBMs.