Source : The Star, Malaysia, 23 Nov 2004
By : Tan Cheng Li
  

 
Wild birds more of a victim than culprit  
   
Experts say culling wild birds will not stop avian influenza  
   
Hysterical and ill-informed – that’s how bird experts described calls to cull wild birds to check the spread of the deadly bird flu. Fortunately, such a call to cull the open-bill storks in Thailand in July was subsequently called off.

Wild birds have been blamed for spreading the disease since several birds were detected with the H5N1 virus. But while it is common for wild birds, particularly waterbirds, to carry strains of avian influenza virus, there is little to show that they are able to spread the highly pathogenic H5N1.

 
  Herons at rest in Hong Kong’s Mai Po nature reserve. A grey heron infected with bird flu was found dead near the reserve this month, and news of this re-ignited fears about the ability of wild birds to spread the disease.
   

“Currently there is no evidence that humans have been affected with H5N1 influenza virus through contact with wild birds. All reported human infections have been associated with contact with domestic poultry,” writes Leslie Dierauf, director of the US Geological Service National Wildlife Health Centre in a wildlife bulletin.

Furthermore, highly pathogenic influenza viruses have rarely been found in wild birds. In Hong Kong, only two birds have been found with the H5N1 virus – a grey heron and a peregrine falcon.

Scientists did not dismiss the possibility that the infected falcon, detected in a test of 6,000 wild birds, had picked up the pathogenic virus in poultry or poultry waste as it was found near two chicken farms.

In another survey in Italy, Bologna University virologist Dr Mauro Delogu found one herring gull out of 100 sampled to have a strain of highly pathogenic virus.

Locally, tests on waterbirds by the Veterinary Research Institute throughout the year did not find any avian influenza virus.

Director Dr Syarifah Syed Hassan says waterbirds collected from Pulau Layang-layang, off Sabah, were also free of the H5N1 virus. In September, there was fear that the birds carried the virus because five navy men had fallen ill with flu symptoms, after burying 20 dead birds found there. The seamen were subsequently cleared of bird flu.

So rather than spreading the deadly virus, wild birds could have fallen victim after catching the virus from farm fowls.

“This particular variant is unusual because it can make wild birds, especially ducks, sick. This is completely different from most other avian influenza viruses,” says Carol Cardona, a poultry extension veterinarian at the University of California-Davis.

Avian influenza viruses circulate freely in populations of wild birds (primarily ducks and shorebirds) throughout the world, and without the birds showing any sign of illness.

“In natural populations of wild birds, these viruses appear to be stable,” says Cyprus-based Dr Hugh A. Buck, a veterinary doctor and founding member of the Oriental Bird Club. “The serotypes of virus so far isolated from wild birds, including ducks, have been almost invariably low pathogenic and do not immediately cause influenza in domestic birds.”

However, the virus mutation rate increases when it is transferred and adapts to a new host species, which can result in increased virulence. Dr Bucks says viruses responsible for disease outbreaks in domestic poultry in the past have segments of genes that can be traced to strains of avian influenza virus historically found in wild waterbirds.

Modern day intensive poultry farming with highly crowded cages provides the ideal condition for viruses to mutate to highly pathogenic forms, and this is the crux of the problem.

“The major transmission from farm to farm is unquestionably movement of infected poultry and poultry products, and wild birds are only a scapegoat,” says Dr Buck.

The Food and Agriculture Organisation has urged Asian countries not to cull wild birds, stating that it will not help to prevent or control avian influenza outbreaks. It says wild birds are an important element of the ecosystem and should not be destroyed.

Conservation group BirdLife International says future risks of disease transmission from wild birds can be reduced through appropriate conservation measures, such as putting aside reserves for migratory birds where they are not trapped or hunted and their habitats are not encroached by farming.

The hunting and keeping of wild birds carries the risk of transmission of flu-like viruses from wild birds to domestic birds, and the remote possibility of transmission to humans.

So trading of wild birds in markets has to stop.

 
   
   

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