THE INFLUENZA VIRUS

1
THE INFLUENZA VIRUS
2
Classification
RNA virus
Family
Genus
Types
Kingsbury DW. In Fields BN et al., eds.
Virology. 2nd Edn. New York Raven Press 1990
107687. Photo courtesy of Linda Stannard,
University of Cape Town, South Africa.
3
Structure segmented and enveloped viruses
Kingsbury DW. In Fields BN et al., eds.
Virology. 2nd Edn. New York Raven Press 1990
107687.
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
The virus nomenclature
Classification of the human influenza viruses
For example A / Beijing / 32 / 92 (H3N2)
A virus type, here A
Beijing place where the strain was isolated
32 strain number
92 year of first isolation
H3N2 subtypes H3 and N2 virus type, here 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

8
(No Transcript)
9
By courtesy of APACIAsia-Pacific Advisory
Committee on influenzawww.apaci-flu.com