General Facts on 2009 H1N1


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"While the virus continues to spread among humans worldwide, the role of animals has not yet been demonstrated  in the epidemiology or spread of the pandemic H1N1 2009" - OIE

Structure of 2009 H1N1 Virus

flu structureH1N1 structure
Schematic stucture of a typical Influenza A virus2   Schematic structure of the 2009 Influenza A (H1N1) virus1.


The Influenza A virus is an envoloped virus containing 8 single-stranded negative RNA segments in its genome2,3:

  • PB1, PB2, & PB3: encodes RNA polymerase (PB = polymerase basic)

  • HA: encodes surface protein hemagglutinin 

  • N: encodes surface protein neuraminidase 

  • NP: encodes nucleoprotein 

  • M1 & M2: encodes two different matrix proteins

  • NS1 & NS2: encodes non-structural proteins

According to studies done by NIH4, the HA of the 2009 H1N1 is much less efficient at binding to respiratory epithelium than other viruses that infect human. Furthermore, their research also suggest that the 2009 H1N1 virus does not have a version PB2 that has been linked to efficient virus transmission. 

The 2009 H1N1 virus is a quadruple reassortment of avian-, swine-, and human-origin genes5,6:

  • Avian genes: PB2  & PA
  • Swine genes: HA, NP, & NS (North American lineage)
  • Swine genes: NA & MP (Eurasian lineage, not previously identified in North America)
  • Human genes: PB

Source: Garten et al3
Animation on origin of Novel Influenza H1N1 can be found at Food & Agriculture Organization of United Nations website


1.Center for Disease Control (CDC) (2009). Images of Influenza A Viruses. Accessed September 24, 2009.

2.     Wikepidia (2005).  Influenza A Virus. Accessed September 24, 2009.

3. Garten, R., Davis, C. T., Russell, C., Shu, B., Lindstrom, S., Balish, A., et al. (2009). Antigenic and genetic characteristics of swine-origin 2009 A(H1N1) influenza viruses circulating in humans. Science, 325(5937), 197.

4. National Institute of Health (NIH) (2009). New insights into Novel H1N1. Accessed September 24, 2009.

5. Godson, Dale (June 2009). Influenza in Swine and the Novel H1N1 virus. Saskatchewan Veterinary Medicine Association (SVMA).

6. Rungrotmongkol, T., Intharathep, P., Malaisree, M., Nunthaboot, N., Kaiyawet, N., Sompornpisut, P., et al. (2009). Susceptibility of antiviral drugs against 2009 influenza A (H1N1) virus. Biochemical and Biophysical Research Communications, 385(3), 390.


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