Avian influenza classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Yazan Daaboul, M.D.

Classification

Classification of avian influenza may be based on either the pathogenicity of the virus or the viral genetics (influenza subtypes). To date, only influenza type A has been associated with avian influenza.

Pathogenecity of the Virus

Avian influenza may be classified based on the pathogenicity of the virus:

• Low pathogenic avian influenza (LPAI)

Mild/no clinical manifestations among humans

May convert to highly pathogenic avian influenza

• Highly pathogenic avian influenza (HPAI)

Moderate/severe clinical manifestations among humans

Viral subtypes H5 and H7 are associated with HPAI

Subtypes Based on Molecular Viral Genetics

• To date, only influenza type A has been associated with avian influenza. Neither influenza B nor influenza C is associated with avian influenza.
• Although avian influenza has many subtypes of haemagglutinin (HA) and neuraminidase (NA), only 3 subtypes have been associated with human infections.
• The table below lists the subtypes of influenza A that have been associated with avian influenza in humans:

Influenza Subtype	Number of Subtypes	Pathogenicity	Clinical Manifestations
			Influenza A H5	At least 9	May be either HPAI or LPAI	May cause either mild or severe/fatal clinical manifestations
Influenza A H7	At least 9	May be either HPAI or LPAI	May cause either mild or severe/fatal clinical manifestations
Influenza A H9	At least 9	Only reported as LPAI	Less likely to cause infections in humans