Influenza A virus subtype H5N1

H5N1 is an influenza A virus subtype defined by its hemagglutinin 5 and neuraminidase 1 surface proteins. Some H5N1 lineages cause highly pathogenic avian influenza and can infect mammals, including humans.

Hemagglutinin: A viral surface protein that binds host-cell receptors and helps influenza viruses enter cells. H5N1’s H designation identifies its hemagglutinin subtype, which helps determine host-cell binding.
Highly pathogenic avian influenza: A severe poultry disease classification based on influenza virus effects in chickens or on specific viral genetic features. Many H5N1 outbreaks in poultry are classified as highly pathogenic avian influenza.
1996 H5N1 outbreak in Guangdong: The first recognized emergence of the H5N1 lineage that later caused major outbreaks in poultry and humans. This outbreak marks the lineage’s emergence before its spread beyond southern China.
Influenza A virus subtype H7N9: An influenza A subtype that caused severe human infections after exposure to infected poultry, especially in China. H7N9, like H5N1, is an avian-origin subtype associated with severe human disease.
Neuraminidase: An influenza surface enzyme that cleaves sialic acids, helping newly formed viruses leave infected cells. H5N1’s N1 designation identifies this protein subtype, a target of antiviral drugs.
Avian influenza surveillance: The systematic testing of birds and environments to detect and track avian influenza viruses. Surveillance can reveal H5N1 circulation before or during outbreaks in poultry and wildlife.
1997 Hong Kong H5N1 outbreak: An outbreak in which H5N1 infected poultry and 18 people in Hong Kong, killing six of them. The human cases established that this avian virus could cause severe disease in people.
Influenza A virus subtype H5N6: An avian influenza A subtype with the H5 hemagglutinin and N6 neuraminidase proteins. H5N6 shares the H5 surface protein but has a different neuraminidase subtype.
Antigenic shift: An abrupt change in influenza viruses when gene segments reassort, potentially producing viruses with new combinations of traits. Reassortment could alter H5N1’s properties if it exchanges gene segments with another influenza virus.
Poultry vaccination: The use of vaccines to reduce disease and transmission of infectious agents in domestic poultry. Vaccination is one tool used to limit H5N1 losses and spread in poultry.

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