- Influenza virus A
- Influenza virus B
- Influenza virus C
Influenza virus type A:
Influenza virus type A is the most common one with many natural hosts among wild aquatic birds. Sometimes the influenza virus type A may be transmitted to other species and so it can cause sudden outbreaks in domestic poultry, pigs and animals. The influenza virus type A is the most virulent and it is the cause of most severe diseases. The most common influenza virus type A subtypes include:
- H1N1 (responsible for flu epidemics in Spain in 1918, as well as Swine flu in 2009)
- H2N2 (responsible for Asian Flu in 1957)
- H3N2 (caused flu epidemics in Hong Kong in 1968)
- H5N1 (pandemic threat in the flu season of 2007-2008, bird flu)
- H7N7
- H1N2
- H9N2
- H7N2
- H10N7
Influenza virus type B:
Influenza virus type B infects mainly humans and it is much less common than influenza virus type A. As the influenza virus type B mutates 2 to 3 times slower than type A it is less genetically diverse. Due to its little antigenic diversity many humans naturally acquire immunity to influenza virus type B at an early age, yet lifelong immunity is not possible. Pandemics of influenza virus type B hardly any occur even though it can sometimes infect the seal and the ferret.
Influenza virus type C:
Influenza virus type C can infect humans as well as dogs and pigs. It can rarely cause epidemics, but it causes mild disease.
