Bird flu: how far and fast can it spread?

N. Gopal Raj

Although migrating wild birds are the prime suspects in the spread of the H5N1 virus, there are no definitive conclusions.

THIS YEAR, the deadly strain of bird flu known as H5N1 has dramatically expanded its range out of countries in East and South-East Asia where outbreaks began in 2003. Since then, this bird flu has led to the death or slaughter of some 140 million domestic birds, resulting in losses to the Asian poultry industry estimated at around $10 billion. Worse, the virus has shown that it is capable of infecting humans and claimed the lives of 60 people.

Until recently, the outbreaks were restricted to Indonesia, Vietnam, Thailand, Laos, Cambodia, and China, points out the Food and Agriculture Organisation (FAO). In May to July this year, many thousand wild waterbirds were found to have died at Qinghai Lake in western China, and the H5N1 virus was isolated from the dead birds. In late July, outbreaks of the virus in poultry and wild birds were reported from Siberia in Russia and in neighbouring Kazakhstan. In early August, authorities in Mongolia reported that many migratory birds at two lakes died after being infected by the lethal strain.

Recently, outbreaks of this bird flu have been confirmed in Turkey and Romania. In both countries, thousands of domestic birds have been destroyed in and around the places where the virus was discovered, and the cull is continuing in a desperate attempt to stop the disease from spreading.

Although migrating wild birds are the prime suspects in this spread of bird flu, the extent of their involvement is uncertain. The evidence implicating wild birds is circumstantial. A “smoking gun” in the form of migratory birds infected with H5N1 shedding the virus in their droppings and secretions and healthy enough to fly long distances has still not been found (see “Are wild bird villains or victims,” The Hindu, August 27).

Lack of such evidence, however, does not rule out the possibility that some species of migratory birds are capable of harbouring the virus and remaining healthy. After visiting Russia, an expert team from the World Organisation for Animal Health (OIE) recently concluded that “in certain conditions migratory birds could carry the Asian H5N1 influenza virus to other parts of the world.”

In the absence of specific information about which species of migratory birds might be capable of acting as carriers of the virus, countries in Europe, the Middle East, South Asia, and even South-East Asia that are currently free of the bird flu are making frenzied preparations in case wild birds bring the virus to their shores.

If migrating wild birds are indeed carrying the H5N1 virus, there would be a risk of the virus being passed on to poultry flocks. Wild birds infected by bird flu shed vast quantities of the virus in their droppings and secretions. So poultry flocks can become infected with these viruses in a number of ways, including:

Poultry being free to mix with wild birds.

Wild birds may defecate while flying and their droppings can fall in open fields where there are poultry.

Water that poultry drink comes from a source, like a lake, that is contaminated by droppings from infected wild birds.

Food that poultry eat can be contaminated with droppings from infected wild birds.

Humans, vehicles, and objects such as farm implements can become contaminated through contact with droppings from infected wild birds, and carry the virus to poultry.

Alternate routes

Considering that the role of migrating birds in spreading H5N1 has not been proven, other routes for this lethal strain of bird flu to enter the country must also be borne in mind and guarded against, says Taej Mundkur of Wetlands International. In the bird trade, millions of wild and caged birds are sold and transported, sometimes illegally. Earlier this year, two mountain hawk eagles smuggled into Belgium from Thailand were found to be infected with the virus. The trade in bird meat, meat products, egg and egg products, and feathers; and the religious practice in parts of South and South-East Asia of releasing captive birds to gain spiritual merit could also spread bird flu.

Minimising the risk to poultry

“Once domestic birds are infected, avian influenza outbreaks can be difficult to control and often cause major economic impacts for poultry farmers in affected countries, since mortality rates are high and infected fowl generally must be destroyed — the technical term is “culled” — in order to prevent the spread of the disease,” points out the FAO. Moreover, despite such culling, the H5N1 virus is still rampant in several South-East Asian countries.

An easy-to-read brochure published by the FAO “Prevention and control of Avian Flu in small scale poultry: A guide for veterinary paraprofessionals in Cambodia,” which can be freely downloaded from the Internet, gives simple tips that smallholders can follow to protect their flocks.

According to this guide, there are three basic principles to protecting a farm:

Keep birds in good condition so that they are able to resist disease better. This requires good access to clean water and adequate food, adequate housing for the birds and receiving de-worming products and vaccination.

Keep the poultry in a protected environment. Ideally, poultry should be kept in a closed building.

Control entry to the farm. People, wheeled vehicles, implements, animals brought from elsewhere, and even dogs or cats carrying dead animals can bring the virus to the farm. Visitors should be kept away from where poultry live and eat. A bucket of water and soap kept handy helps reduce the risk of infection.

Risk to humans

No outbreak involving the H5N1 virus has so far been reported anywhere in India, either among wild birds or poultry.

In the event that such an outbreak does occur in India, according to the World Health Organisation the main route for human infection is through direct contact with infected poultry or surfaces and objects contaminated by their droppings. Risk of exposure to the virus is considered highest during slaughter, de-feathering, butchering, and preparation of poultry for cooking. “There is no evidence that properly cooked poultry or poultry products can be a source of infection,” said the WHO in a recent update.

Moreover, although countless people would have lived close to and handled the millions of domestic birds infected with the deadly virus in South-East Asian countries, there have been just 117 confirmed cases of human infection since December 2003 according to the WHO records.


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