Molecular epidemiological investigation of AIV H9N2 subtype in broilers in North and Northeast China

Abstract

Avian Influenza (AI) is the most significant disease problem of poultry being the cause of high mortality and is zoonotic as well. The virus mutates easily and thus generates new strains. There was a need to look at the current scenario of AI virus being circulating in certain parts of the China and its genetic distance from the vaccine strain. For this purpose, the study was carried out by collecting 864 tracheal and lung tissue samples showing lesions from commercial broiler farms, slaughterhouses, liver broiler markets, and cities of the China. Avian Influenza Virus was isolated from 67 lung + tracheal tissues, of these 35 strains of AIV were confirmed positive by PCR and sequencing. The results of genetic distance analysis revealed that 6 strains of the virus were grouped into H9.4.2.5.1 subfamily, while 29 strains were grouped in to H9.4.2.5.2 subfamily. The HA gene homology analysis revealed that 35 strains had 92.1 to 99.7% homology among themselves. The homology between the 35 strains and the vaccine strain (Y280) was 86.1 to 92% and the homology between the 35 strains and the SY/97 strain was 86.4 to 91.8%. The study showed that field virus has main two subfamilies, but both of these differ on basis of genetic analysis with the two vaccine strains.