Types and causes of flu

Types and causes of flu

Types of flu

There are three types of flu viruses. The annual flu epidemic is usually caused by type A and B viruses. Type C virus also causes flu, however the symptoms are much less severe.

  • Type A Flu: This flu virus is capable of infecting both humans and animals. It is more common, however, for people to suffer the ailments associated with this type of flu. Wild birds are the most common hosts for this flu virus. Other animals known to carry the type A virus are ducks, chickens, pigs, whales, horses and seals. Type A is the flu virus that is generally responsible for large flu epidemics and is constantly changing. The A2 subtype flu virus is generally spread by people who are already infected. Influenza A may be broken down into further subtypes based on H and N antigens (proteins carried on the virus surface), hence the names H1N1 and H2N3 flu.
  • Type B Flu: Type B viruses are only found in humans. This virus type may cause a less severe infection than type A, but can occasionally still cause more severe symptoms and infections. Type B viruses are not classified by subtype and don’t cause pandemics.
  • Type C Flu: As with type B viruses, type C is also more commonly found in people. A milder virus type than A and B, most infected with this type do not become very ill. Type C flu viruses thus do not cause epidemics.

Other types of flu viruses include:

  • Bird Flu (H5N1): Also known as avian flu, H5N1 is a viral infection spread from bird to bird. Birds can be infected by type A viruses and all its subtypes. There are three main subtypes of bird flu: H5, H7 and H9. Of the three H5 and H7 are the most severe, while H9 is less dangerous. Birds are not capable of carrying type B or C viruses, however, the main reason bird flu is cause for concern in humans is its ability to be passed from wild birds to poultry. As poultry is a commonly farmed, humans are at risk due to frequent close contact (handling the bird). The risk, however, is low in most people as the virus does not typically infect humans. People cannot catch the virus from consuming chicken or eggs. H5N1 is deadly for most birds and can be for humans and other mammals as well. Close contact with an infected bird or bird droppings has been known to infect humans with the virus, but cases where the infection has spread from human to human have been reported as extremely rare.
  • Swine Flu (H1N1): In 2009 H1N1 flu spread fairly quickly around the globe and was soon declared a pandemic by the World Health Organisation. As with other flu viruses, swine flu is highly contagious and easily caught when in close proximity to an infected person or surface they have touched, and then touching your own mouth or nose. As with bird flu, H1N1 infections are not as a direct result of consuming pork products. A person infected with H1N1 begins spreading the virus through infected droplets of saliva and bodily fluids at least a day before symptoms begin and is contagious for as many as 7 days thereafter. Children with the virus can be contagious for up to 10 days. Like seasonal flu, H1N1 can cause more serious health concerns such as pneumonia, lung infections and other respiratory problems, and for this reason is now included in the flu vaccine.
  • Stomach Flu (gastroenteritis): Stomach flu symptoms are often mistaken as the flu virus, but it is not the same. Stomach flu occurs when your stomach and intestines (gastrointestinal or GI tract) become inflamed and irritated. Causes of stomach flu range from bacteria, viruses and parasites to food reactions (particularly in dairy products) and unhygienic water. Symptoms that are similar include fever, congestion, muscle aches, headache, swollen lymph glands and fatigue. Those suffering from stomach flu will also experience abdominal cramping or pain in the stomach (or sides), nausea, vomiting and diarrhoea.

Causes of Flu

Only virus types A, B and C cause the flu. Seasonal outbreaks are largely caused by type A and B. Type C is usually responsible for milder respiratory symptoms.

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