March 25, 2004

 

 

Poultry Vaccination Could Lead To New Strains

 

Campaigns by Asian countries to save poultry flocks by vaccinating them against bird flu are a 'ticking time bomb' that will encourage the risk of a devastating pandemic among humans.

 

China and Indonesia are rushing to vaccinate their chickens against the H5N1 bird flu virus as a low-cost alternative to destroying flocks, and other nations are mulling whether to follow suit.

 

Yet without close surveillance, this approach is potentially dangerous, the British weekly says in next Saturday's issue.

 

The main problem is that the vaccination is not 100 per cent effective. It does stop birds from falling sick, but enough of the virus remains to replicate in their bodies.

 

That means an epidemic could quickly spread among unvaccinated animals or when the vaccination programme ends, and the virus also has the chance of evolving into a newer form that sidesteps the vaccine formula.

 

New evidence for this risk has come from Mexico, which stopped an outbreak in 1995 of H5N2 virus, a cousin of H5N1, among its poultry by vaccinating the birds.

 

In a study due to be published in the Journal of Virology, US Department of Agriculture expert David Suarez and colleagues report that bird flu viruses isolated from Mexican chickens after the 1995 vaccination campaign have mutated substantially and are now 'increasingly different' from the vaccine strain, New Scientist says.

 

The research adds to suspicions among animal health experts that China's crash programme to vaccinate its flocks after the outbreak of H5N1 among humans in neighbouring Hong Kong in 1997 helped the current strain of virus to emerge.

 

China last week declared that its outbreaks of bird flu among poultry were over.

 

Most veterinary experts prefer to control livestock epidemics by destroying sick and exposed animals instead of vaccinating them.

 

New Scientist says: 'Such surveillance systems will be a tall order for the Asian countries that are vaccinating or plan to.'

 

These countries 'will be carrying out an uncontrolled experiment in viral evolution that could ultimately lead to a human pandemic.'