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How are influenza viruses named?

How are influenza viruses named? They follow an internationally established formula, that you will see in vaccine leaflets, for example.
Several flu viral particles
© 2017. Universidad Complutense de Madrid

The influenza viruses are named by a formula established by the international Committee of Taxonomy.

This formula is, for example, in the spc, prospectus or leaflets of vaccines against flu. For this reason, it is important that you understand it well.

The taxonomic expression is as follows:

  1. The first term indicates the type of virus, A, B, or C. In our case, the animal viruses that produce diseases are type A. In humans, some B viruses can also produce clinical disease.
  2. Next, the animal species from which the virus has been isolated is indicated: equine, swine, chicken, duck, turkey… In human viruses it is not specified.
  3. The next term is the geographical origin of the viral isolate, e.g. Wyoming, Sydney, Thailand, Sweden, Mexico, etc., and may correspond to a country, city, region, etc.
  4. The fourth place corresponds to the reference number of the strain.
  5. Then, the year when the virus was isolated is mentioned.
  6. Last, and in brackets, the numbers of the hemagglutinin and the neuraminidase. To date, 18 hemagglutinins and 11 neuraminidases have been described in different animal species.

This will be the result:

Virus A/animal species/geographical origin/reference number/year/hemagglutinin-neuraminidase (H-N) formula

The same type of hemagglutinin can be present in viruses isolated from different species of animals, including both wild and domestic. For example, H3 may be associated with human and equine viruses, among others, and N1 with chicken and swine viruses.

Some examples of the nomenclature of viruses isolated, identified and classified in reference laboratories of different countries and present in the international list of influenza viruses are:

Species Strain
Human A/Ontario/59/2015 (H3N2)
Human A/Egypt/N5565/2014 (H5N1)
Human A/Aragon/271/2014 (H3N2)
Human A/Rome/623/2009 (H1N1)
Human A/Shanghai/01/2014 (H7N9)
Swine A/swine/Illinois/A0147397/2011 (H1N2)
Swine A/ swine /Denmark/16496-1/2008 (H1N1)
Swine A/ swine /Indiana/A01260479/2014 (H3N2)
Chicken A/chicken/Vietnam/NCVD-185/2008 (H5N1)
Chicken A/ chicken /Yogyakarta/159/2011 (H5N1)
Chicken A/ chicken /Shantou/4832/2014 (H7N9)
Chicken A/ chicken /Fujian/SN2/2012 (H9N2)
Duck A/duck/Hong Kong/938/80 (H10N1)
Duck A/duck/Mongolia/129/2010 (H7N9)
Turkey A/turkey/Indiana/16-001403-1/2016 (H7N8)
Horse A/eq/Newmarket/93 (H3N8)
Horse A/eq/Suffolk/89 (H3N8)
Horse A/eq/Berlin/13/02 (H3N8)
Horse A/eq/California/2/2010 (H3N8)

Often, only the combination of hemagglutinin and neuraminidase are mentioned when we talk about influenza viruses. However, we should always indicate the species in which it circulates.

The species of interest that we will talk about in this course in regard to influenza will be chickens, pigs and horses, in addition to human Influenza, which we will discuss briefly. We will highlight the important role that waterfowl viruses have in the epidemiology and transmission of viruses.


Influenza viruses are very prevalent. For this step, you have to look for some information and share it with the other learners.

  1. Search the most relevant and frequent types of viruses in the following animal species, indicating their combination of hemagglutinin and neuraminidase: human, porcine, chicken, equine, duck, turkey, whale, seal, bats and dog.
  2. Search the viruses detected or associated with outbreaks of avian influenza (highly pathogenic, hemagglutinins H5 and H7) in the annual releases of diseases reported by different countries to the World Organization of Animal Health (OIE) in the years 2005 and 2015, following the link OIE- animal health in the world-update of highly pathogenic avian influenza (H5 and H7). What differences can you see in the combinations of HA and NA in isolates from 2005 and 2015?

Compare the results and share your conclusions with the other learners in the Comments.

© 2017. Universidad Complutense de Madrid
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Animal Viruses: Their Transmission and the Diseases They Produce

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