Influenza or as it is commonly known the flu is a contagious disease caused by an RNA virus of the orthomyxoviridae family. The name comes from the old medical belief in unfavourable astrological influences as the cause of the disease.
There are three types of the virus:
- Influenza A viruses that infect mammals (humans, pigs, ferrets, horses) and birds
- Influenza B viruses that infect only humans
- Influenza C viruses that infect only humans
The virus attacks the respiratory tract, is transmitted from person to person by droplets, and causes the following symptoms:
- Tiredness (can be extreme)
- Dry cough
- Sore throat
- Nasal congestion and sneezing
- Body aches
Influenza is an extremely variable disease: similar viruses are found in pigs and domestic fowl. In areas where there are high concentrations of humans, pigs and birds in close proximity, such as parts of Asia, simultaneous infections across species enable genetic material to be exchanged between the various strains of flu. This appears to be the principal method by which new infectious strains arise. It is believed that sooner or later, a recombination may occur to produce a strain as lethal as the 1918 virus. In late 1997, a new strain of influenza originating from chickens infected 18 people in Hong Kong, of whom 6 died. This strain did not appear to be readily transmissible from human to human, but such a high mortality rate, and the possibility of a further recombination to make it more infectious, meant that the risk was considered so great that all domestic poultry in Hong Kong was slaughtered. As of April 2002, there have been no further human infections with this particular strain.
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It is possible to get vaccinated against Influenza, however due to the high mutability of the virus the vaccine is usually only good for a year or so. The World Health Organization co-ordinates the contents of the vaccine each year to contain the most likely strains of the virus to attack the next year. The vaccine is usually recommended for anyone in a high-risk group who may suffer complications from a real flu attack.