Flu Virus Classification And Symptoms
Flu virus classification includes three types of influenza viruses from the Orthomyxoviridae family. Flu viruses are included in the Baltimore classification system in the group V, of RNA viruses and they are known as influenza viruses. This type of virus infects birds, mammals and humans.
There are three types of influenza virus, Influenza A, influenza B and influenza C. Influenza A is the type of influenza that is responsible for the largest pandemics and it is the type that mutates the fastest, 2 to 3 times faster than the other influenza viruses. The classification of influenza virus A is established based on the hemagglutinin (H or HA) and neuraminidase (N or NA) proteins that are visible on the surface of the virus. There are 16 types of hemagglutinin and 9 of neuraminidase so theoretically 144 subtypes of influenza A virus even though in practice only a part of these have been observed. It affects birds, mammals and humans and the most significant subtypes affecting humans are H1N1, H1N2 and H3N2 viruses. The H1N1 influenza virus is the one that caused the Spanish flu pandemic in the first decade of the 1900s and also the swine flu pandemic in 2009. The H5N1 subtype is the one thought to potentially cause a pandemic avian flu. Influenza B virus affects almost exclusively humans but it is not as common as influenza A. The virus is also responsible for influenza infections in seals. Due to its reduced antigenic diversity, immunity to this type of influenza is normally acquired for most of the people at early ages. Influenza B pandemics occur almost never. Influenza C generally affects humans and pigs and may be responsible for local epidemics although it is less common than the other influenza types.
The most recent pandemic was caused in 2009 by the swine flu virus, the H1N1 subtype of influenza A virus. The virus affects pigs but it can be transmitted to people who work with pigs, especially to those with a high degree of exposure. The farm workers are considered the most at risk of a zoonotic infection with this type of virus. The stomach flu or gastroenteritis is the inflammation of the gastrointestinal tract which has similar symptoms to the flu even though it is not caused by influenza viruses. The flu virus symptoms may involve fever, sore throat, chills, muscle pain and couching, and general discomfort. The flu caused by influenza can be life threatening if it evolves to pneumonia. The disease can produce nausea or vomiting in children.
The flu virus classification includes three types of influenza viruses, A, B and C from which only influenza C virus is believed to be the most stable virus type causing only mild diseases.