H9N2 Hong-Kong

The H9N2 subtype of Influenza A virus is a significant pathogen in both avian and mammalian species. The strain A/Hong Kong/1073/99 (H9N2) is particularly notable due to its role in the epidemiology of avian influenza and its potential implications for human health.

The H9N2 influenza virus has been endemic in various avian species across the Eurasian continent. The first outbreak in China occurred in Guangdong province between November 1992 and May 1994, affecting multiple chicken farms and causing significant economic losses due to high mortality rates and reduced egg production . The virus spread rapidly across China and became the most prevalent subtype in chickens by 1998 .

The H9N2 virus is known for its extensive gene reassortment, which has contributed to its adaptation in both poultry and mammalian hosts . The hemagglutinin (HA) gene of H9N2 viruses can be divided into Eurasian avian and American avian lineages. The Eurasian avian lineage includes three distinct lineages: A/chicken/Beijing/1/94-like (BJ/94-like), A/quail/Hong Kong/G1/97-like (G1-like), and A/duck/Hong Kong/Y439/97 (Y439-like) .

Human infections with H9N2 viruses have been documented, with the first cases reported in Hong Kong in 1999 . These infections were associated with mild respiratory illnesses. The detection of antibodies to H9 hemagglutinin in poultry workers suggests that there may have been additional unrecognized infections .

The recombinant strain A/Hong Kong/1073/99 (H9N2) is glycosylated with N-linked sugars and produced using baculovirus vectors in insect cells . This strain has been used in various studies to understand the antigenicity and safety of H9N2 vaccines .