Deadly virus: how it began and why it is spreading our way

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The Independent Online

What is bird flu and why is it a threat?

Like humans, birds can suffer from influenza but unlike the human illness, the bird disease is caused by avian flu viruses. Normally these viruses do not infect humans but some years ago a strain or subtype of avian flu virus called H5N1 was found to infect people, killing up to half of those infected. The virus does not possess the genetic traits that allow it to pass easily from one person to another, however the fear is that as more birds and people become infected, a mutation allowing person-to-person transmission is increasingly likely. If this occurred, then a global epidemic of a highly lethal form of human flu would be likely.

How can we control an outbreak of the H5N1 virus in humans?

A vaccine against H5N1 is undergoing clinical trials and early results are encouraging. However, further work will be needed before it is ready for general use. An antiviral drug called Tamiflu, made by the Swiss company Roche, is known to be effective provided it is taken in the earliest stages of the infection, or even as a preventive. To really control a pandemic it is necessary to nip it in the bud before it even becomes a local epidemic. Most scientists believe that if H5N1 infects anyone in Britain, it will be too late to control its further spread.

What is the history of the H5N1 virus?

The strain of avian flu most likely to cause a global pandemic among humans is the H5N1 subtype which was first detected in 1961 in terns living wild in South Africa. In 1997 the first transmission from birds to humans was reported during an outbreak of avian flu in Hong Kong. Eighteen people suffered respiratory infections and six died. The outbreak seemed to be controlled but it re-emerged in south-east Asia in late 2003 and early 2004 when 100 million birds were culled. In early 2004 there were 12 confirmed cases of H5N1 in Thailand and 23 in Vietnam, resulting in 23 deaths. Again the virus seemed to come under control but in late June 2004 it re-emerged again in several Asian countries, notably Cambodia, China, Indonesia and Malaysia as well as Thailand and Vietnam. To date there have been more than 100 cases in humans and about 60 deaths. The virus has now spread to birds in central Asia, Japan and Russia.

How is bird flu spread among birds and people?

Avian flu gets into the digestive system of birds and is excreted with faeces. Waterfowl seemed to be particularly vulnerable. It is not known exactly how humans pick up the virus from birds but it is assumed to involve very close contact, perhaps by plucking feathers or in the case of children by playing among infected animals. Eating cooked poultry meat or eggs carries no risk.

Can bird flu infect any other animals?

Pigs are known to be carriers of influenza virus and several swine herds in Indonesia have tested positive for the H5N1 strain, which they probably caught by the pigs coming into contact with chicken manure. Scientists fear that pigs can act as "mixing vessels" for flu viruses. When pigs become infected with two or more types of flu, the viruses can swap genetic information to produce new strains which may be more virulent or infectious than the original viruses.