HANOI (AFX) - Outbreaks of highly pathogenic bird flu may be more established in bird populations and in the environment across Asia than currently realised, the World Health Organization said.
The simultaneous occurrence in several countries of large outbreaks of the H5N1 strain of avian influenza in domestic poultry is historically unprecedented and the present situation may grow worse, the UN agency warned.
"In bird populations, the disease is highly contagious and rapidly fatal, and spreads easily from farm to farm. Wild migratory waterfowl can spread infection to domestic flocks," it said in a statement.
"The potential for further spread of ongoing poultry epidemics, both within affected countries and to other countries, is therefore great."
Thailand today became the latest Asian country to confirm it is suffering from an outbreak of bird flu, a disease that is potentially fatal to humans.
At least five people in Vietnam have died from the H5N1 virus.
Bird flu has also been reported in Japan and South Korea.
A weaker strain, H5N2, has been found at a farm in Taiwan.
The WHO stressed that rapid elimination of the H5N1 virus in bird populations is critical to preventing the emergence of a new influenza virus subtype with pandemic potential.
"The large epidemics of highly pathogenic avian influenza currently seen in poultry, and possible widespread presence of the virus in the environment, increase opportunities for human exposure and infection," it said.
This also increases the risk of human and avian influenza viruses exchanging genes. This, the WHO said, can occur when humans are simultaneously infected by human and avian influenza viruses.
In particular, those involved in slaughtering infected chickens are at risk of "brief but intensive exposure to the virus," it said.
"While rapid culling of infected or exposed flocks is strongly recommended, prevention of infection during culling operations must also be given high priority."
Research has shown that infected birds can shed large amounts of the virus in their faeces. The virus can survive for long periods in the tissues and faeces of diseased birds and in water, especially when temperatures are low.
In water, the virus can survive for up to four days at 22 degree Centigrade and more than 30 days at 0 degrees Centigrade. The virus survives in frozen material indefinitely.
The WHO said that initial results have shown significant differences between H5N1 strains isolated from humans and poultry in Vietnam and those obtained during the 1997 H5N1 outbreak in Hong Kong in 1997.
This, it said, indicates that the virus has mutated.
Work is continuing on the updating of diagnostic kits for the rapid detection of H5N1 infection in humans, and on the development of a prototype virus for use in vaccine manufacturing, the UN agency added.
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