1. THE INFLUENZA VIRUS

2. RNA virus Family: Genus: Types: Classification Type AType B Influenza virus Type C Influenza C virus ORTHOMYXOVIRIDAE Kingsbury DW. In: Fields BN et al., eds. Virology. 2nd Edn. New York: Raven Press; 1990: 1076–87. Photo courtesy of Linda Stannard, University of Cape Town, South Africa.

3. Kingsbury DW. In: Fields BN et al., eds. Virology. 2nd Edn. New York: Raven Press; 1990: 1076–87. Structure: segmented and enveloped viruses 80 to 120 nm Surface antigens Internal antigens Nucleocapsid: Nucleoprotein (NP)-RNA (7 or 8 segments) Matrix protein (M) Lipid bilayer Haemaglutinin (HA) Neuraminidase (NA)

4. Surface glycoproteins Haemagglutinin – H or HA – responsible for pathogenicity of the virus – allows virus to adhere to endothelial cells in the respiratory tract – main determinant of immunity Neuraminidase – N or NA – allows release of newly formed viruses within host – determinant of disease severity

5. Influenza subgroups Influenza A – highly infective – infects many species – causes widespread epidemics Influenza B – found only in humans – capable of producing severe disease – causes regional epidemics Influenza C – causes mild disease – humans are natural hosts, but isolates also found in pigs – does not cause epidemics

6. Classification of the human influenza viruses The virus nomenclature Avirus type, here A Beijingplace where the strain was isolated 92year of first isolation 32strain number H3N2subtypes H3 and N2 virus type, here H3N2 For example: A / Beijing / 32 / 92 (H3N2)

7. Occurrence of influenza A viruses Influenza A viruses 16 HA types 9 NA types Species affected humans, pigs, horses, birds, marine mammals In humans 3 HA types (H1, H2, H3) 3 NA types (N1, N2, N8) In birds all HA types all NA types

9. By courtesy of APACI Asia-Pacific Advisory Committee on influenza www.apaci-flu.com