As is well known, in the past two years, avian influenza has been rampant abroad, with a large number of culling, "home isolation" of chicken flocks, restrictions on introduction, "queuing up to buy eggs", "flying seedlings" and other news frequently seen, seriously threatening the normal breeding order in China. Thanks to China's mandatory immunization policy and the active cooperation of breeding units, highly pathogenic avian influenza in China has been in a preventable and controllable state. However, although inactivated vaccines are used for immunization against low pathogenic avian influenza H9N2 in China, H9N2 still remains prevalent in immunized chicken flocks. In recent years, it has been discovered that H3N8 subtype avian influenza is spreading in chicken flocks, which also deserves high vigilance!

Epidemiological and clinical symptoms:

Since 2022, a disease characterized by mental depression, loss of appetite, respiratory symptoms, and decreased egg production performance has emerged in egg laying and broiler flocks in Guangdong, Guangxi, Fujian, Jiangsu, Sichuan, Shandong, and other regions. The clinical anatomical manifestations are characterized by tracheal ring bleeding, excessive secretion of mucus from the larynx and trachea, significant bronchial obstruction in dead chickens, pulmonary congestion, occasional renal swelling, and liquefaction of egg laying chicken follicles.

Laboratory diagnosis:

Collect throat swabs and throat, trachea, and lung tissue samples from diseased chickens for real-time fluorescence quantitative RT-PCR to detect NDV, ILTV, IBV, H5, and H7 as negative. Influenza universal primers and H3 are positive. Collecting serum from diseased chicken flocks for blood coagulation test, HI results showed significant inhibition of H3 subtype AIV.

Related studies have shown that:

?  The newly emerged H3N8 virus HA gene belongs to the Eurasian avian branch, while NA belongs to the North American branch& nbsp; Six internal genes are closely related to H9N2. At present, the nucleic acid and amino acid sequences of domestic isolates are highly consistent, and the evolutionary tree shows that the isolates are closely related.

?  Relevant literature and experimental data fully demonstrate that H3N8 has strong adaptability to chicken flocks, and the virus has strong horizontal transmission ability and certain pathogenicity. Moreover, domestic scholars have boldly predicted that this virus is currently rapidly spreading in poultry and will affect the health of domestic poultry in the future.

?  In addition, in April 2022, there was a "spillover" incident of human infection with H3N8 virus, and the public health threat of H3N8 avian influenza should also be taken seriously.

Prevention and control suggestions:

Compared with developed countries, China's poultry farming level is relatively backward in terms of farming mode, low level of mechanization, and weak professional level of practitioners. Given this:

?  Standardizing and implementing biosecurity measures in aquaculture farms is an effective means of preventing and controlling diseases. Avoid the invasion of wild birds and the mode of mixed breeding of water and land birds, and disinfect people, animals, and vehicles when entering the site. Strengthen H5 H7、H9、 Vaccination against transmission and Newcastle disease can increase the resistance of chicken populations.

?  At present, the understanding of H3N8 is not mature enough, and it is necessary for research institutions to strengthen epidemiological monitoring and conduct relevant scientific research on H3N8.