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Influenza Virus Resource presents data obtained from the NIAID Influenza Genome Sequencing Project as well as from GenBank, combined with tools for flu sequence analysis and annotation. In addition, it provides links to other resources that contain flu sequences, publications and general information about flu viruses.

Read more about: This resource | Flu database | Flu sequence submission to GenBank | NIAID Influenza Sequencing Project | Influenza virus biology
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Flu Epidemiology
Flu epidemics cause morbidity and mortality worldwide. Each year in the USA, more than 200,000 patients are admitted to hospitals because of influenza and there are approximately 36,000 influenza-related deaths.

Of the three types of influenza virus-A, B and C-the A and B types can cause flu epidemics. Influenza A virus is found in human and many other animals. There are over 100 subtypes of Influenza A virus. All subtypes have been found in wild birds, which are thought to be a natural reservoir of Influenza A virus and the source of influenza A viruses in all other animals.

For example, pigs may be infected with influenza A viruses from different species (e.g., ducks and humans) at the same time, which may allow the genes of these viruses to mix, creating new variants of the hemagglutinin and/or neuraminidase proteins on the surface of the virus (antigenic shift). If these variants spread to humans, then they would not be recognized by the immune system, and so can cause seasonal epidemics of flu. In addition, flu viruses undergo mutations when they spread from place to place, therefore introduce gradual changes in the hemagglutinin and/or neuraminidase proteins (antigenic drift). Each year, it is essential to identify new flu virus variants and produce vaccines against them to avoid flu epidemics.

Influenza virus biology

Influenza A virus particles.
Courtesy of Audray Harris, Bernard Heymann and Alasdair C. Steven, LSBR, NIAMS, NIH.
Influenza viruses belong to the family Orthomyxoviridae. The viral particles are about 80-120 nm in diameter and can be spherical or pleomorphic. They have a lipid membrane envelope that contains the two glycoproteins: hemagglutinin (HA) and neuraminidase (NA). These two proteins determine the subtypes of Influenza A virus. There are 16 H subtypes and 9 N subtypes.

The Influenza A viral genome consists of eight, single negative-strand RNAs that can range between 890 and 2340 nucleotides long. Each RNA segment encodes one to two proteins. More about the replication of Influenza A virus...

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