| Avian influenza(AI),caused by the influenza virus Type A,can affect several species poultry with high mortalities.Avian influenza virus belongs to Orthomyxoviridae in genus Influenza virus A,distributed worldwide.Many species can be infected by the virus.As the reservoir of avian influenza viruses,waterfowl play important role in the transmission of the disease.Big losses can be caused when the disease transmitted from waterfowl to domestic poultry.Meanwhile some strains can infect humans,even cause death.So it is important to perform the epidemiological survey and molecular evolution of avian influenza for prevention and control of the disease and the prediction of pandemic in human and poultry.In this study 2700 serum samples which were collected from 33 farms,9 live bird markets and 3 slaughter houses,and 5840 swab samples collected from 297 flocks including 18 LBMs,143 poultry farms and 5 slaughter houses were used to perform the serological and virological test respectively by simple random sampling.Risk factors were also analyzed in poultry farms by statistics analysis.Serological test indicated that the overall individual qualification rate for H5 and H9 was 84.41% and 94.3%,and the population qualification rate was 86.67%和 98.89% respectively.Samples collected from poultry farms showed higher antibody levels compared with samples from LBMs and slaughter houses.The individual and population positive rate of H7 avian influenza all were negative.Virological tests revealed that the main pathogen existed in most sampling units was H9 avian influenza viruses.Furthermore,one H5N6 subtype highly pathogenic avian influenza(HPAI)was detected from one poultry farms,one H7N9 AIV was detected from one LBM,H3N2 AIV was detected from wild bird habitat.The viruses were proved to be active during October to May.The virus positive rate in yellow-feathered broiler was much higher than other species.AIVs were detected from all regions,but it main existed in Zhongwei and Guyuan.Risk analysis revealed that all-in all-out,intensive bird net,disposal of dead birds,single batch,strict disinfection of movement,no market visiting and no connect with outer people can prevent the disease.Regression module was built by logistic regression,and ROC curve was also constructed.It showed the module has a better degree of fitting and can be used to predict the risk of transmission in poultry farms.Outbreak investigation of H5N6 HPAI in poultry farm was conducted in order to describe the distribution and the potential source of the outbreak.Our results proved that the wild birds which were infected by H5N6 played important role in the introduction of the virus into the poultry farm by contacting with dead local chicken infected by wild birds.The outbreak was controlled by emergency culling and disposal of infected area.From our study we recommended that the poultry farm should enhance the bio-security practice and change the raising pattern,and stocking by law.Meanwhile more investments on science and technologies should be put from the government side in order to improve the development of vaccine with higher efficiency and matching timely for prevention and control of avian influenza.Sixteen isolates of AIVs were used to perform the molecular epidemiology and genetic evolution based on the HA genes.Our results showed that the strain of H3N2 isolated from wild birds had the highest homology with the strain of A/duck/Mongolia/199/2015(H3N8)isolated from Mongolia(98.6%).This indicated the virus may be introduced from neighboring country.The H5N6 AIV was belonged to clade 2.3.4.4 based the HA gene and big mutations were found with 3 H5 AIV strains obtained from Ningxia in 2015.It revealed that alternative vaccine with higher matching should be used on time according to the field strains.One strain of H7N9 isolated in the study had higher homology with the new emerging H7N9 in 2013.More surveillance should be conducted in order to trace and find the mutation of the virus for early warning.The homology of HA genes between 13 H9N2 isolates and vaccine strain was 88.7%-91.4%.It indicated that the obvious drift mutation of the HA gene in H9 viruses had occurred and the current vaccine could not provide enough protection to the field circulating viruses.Furthermore,realtime RT-PCR with Tan Man MGB probes for detection of H5 and H9 AIVs were built in the study in order to meet with the early detection of the AIVs.The methods developed in the study showed high sensitivity and specificity compared with virus isolation and commercial kits,can detect the RNA of the AIVs existed in swabs,organs and fecal samples.These methods provided powerful tools for diagnosis,surveillance and epidemiological survey of avian influenza. |
PDF Full Text Request