Systematic Veterinary Virology

SUB TYPES

• Influenza A viruses have antigenically related nucleocapsid and antigenically related matrix proteins, but are classified into subtypes on the basis of their haemagglutinin (HA referred as H) and neuraminidase (NA referred as N) antigens.
• At present, 15 H subtypes (H1–H15) and 9 neuraminidase subtypes (N1–N9) are recognised. There are three subtypes of avian influenza virus referred as H5, H7 and H9. H5 and H7 can produce low pathogenic and highly pathogenic avian influenza, where as H9 produces only low pathogenic infection.
• Within these subtypes there are number of strains. These strains are formed by combination of any one of H5, H7 or H9 with 9 different NA proteins. The following table lists the details of subtypes and strains of avian influenza viruses

Subtype Characters-Example

• H5
• Nine different strains.
• Produce highly pathogenic or low pathogenic infections.
• Human infection possible, sometimes causing severe illness and death H5N1 (Hong Kong).
• H7
• Nine different strains.
• Produce highly pathogenic or low pathogenic infections.
• Human infection is rare, but can occur among persons who have close contact with infected birds; symptoms may include conjunctivitis and/or upper respiratory symptom H7N7 (Netherlands).
• H9
• Nine different strains.
• Produce only low pathogenic infection.
• Human infection possible H9N2.