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Causes

health-and-fitness Updated: Jan 18, 2008 23:28 IST

Hindustan Times
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Flu viruses, which can infect birds, bear the name of avian influenza. Also, of the three types of flu (A, B and C) that exist, only the influenza 'A' virus affects birds.

The latter is known to be a form of bird flu, which can cause severe illness and have a high rate of mortality among the fowls. Both low and highly pathogenic viruses of the bird flu type have been known to affect humans in recent years and their effect has ranged from mild to severe and irreversible effects on the human body, eventually causing death. Such is the case with the H5N1, H7N3 and H7N7 viruses. Direct contact of the human victims with infected birds or consumption of such untreated meat is proven to be the main cause of bird flu infections.

The name or symbolization of the avian flu viruses derives from combinations of the 3 basic types of influenza 'A' viruses (H5, H7 and H9) with different types of neuraminidase surface proteins (eg N1, N3, N7, N9).

A more important and dangerous mutation is the antigenic shift, by which a completely new influenza 'A' type of virus develops. This usually occurs either by a transmission of the virus from animals (more specifically poultry) to human, or by a combination of human influenza A and animal influenza A genes, giving birth to a completely new subtype. It is believed it takes about 3 months for a vaccine to be developed after the appearance of a new virus strain, so quick action is important when evidence of such mutations is present. If a new subtype of influenza 'A' virus is highly pathogenic and can find a way of being transmitted easily from person to person, then an outbreak of influenza pandemic is very likely to occur. Such is the case with the current bird flu virus, that such a pandemic is highly possible. That being the case, specialists warn such a world wide epidemic could claim the lives of up to 150 million people.