Genetic Evolution of Influenza A(H7N9) virus in China

The eight genes of the Influenza A(H7N9) virus are closely related to avian influenza viruses found in domestic ducks, wild birds and domestic poultry in Asia. The virus likely emerged from a reassortment, a process in which two or more influenza viruses co-infect a single host and exchange genes.
[Image: CDC]
This can result in the creation of a new influenza virus. Experts think multiple reassortment events led to the creation of the novel Influenza A(H7N9) virus  These events may have occurred in habitats shared by wild and domestic birds and/or in live bird/poultry markets, where different species of birds are bought and sold for food. As the above diagram shows, the Influenza A(H7N9) virus likely obtained its HA (hemagglutinin) gene from domestic ducks, its NA (neuraminidase) gene from wild birds, and its six remaining genes from multiple related H9N2 influenza viruses in domestic poultry.

While infected poultry remain the most likely culprit, the definitive answer to exactly how the Influenza A(H7N9) virus is spreading in China, and occasionally manages to infect humans, remains frustratingly elusive.

Major antigenic shifts are often a prelude to pandemic influenza[1].

[1] Cunha: Influenza: historical aspects of epidemics and pandemics in Infectious Diseases Clinics of North America - 2004

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