Burial has been a key method of disposing birds in avian flu outbreaks across the world, but US researchers have now discovered that the virus could remain infectious for up to two years.

The findings raise questions over current disposal methods, particularly in the US and Asia where hundreds of millions of birds have been culled and disposed of in landfill. During one outbreakon Virginia farms in 2002, four million birds were culled and buried.

“There are a lot of birds at landfills,” said Shannon Bartelt-Hunt, an environmental engineer at the University of Nebraska-Lincoln. “If you think of landfills as reservoirs, you could have birds as vectors.

In the study, a team led by Dr Bartelt-Hunt studied the survival of the H6N2 avian flu virus site by monitoring the leachate from a landfill site. They also related the survival time with factors such as temperature and pH.

The team found the time taken for the virus to be inactivated ranged from 30 to more than 600 days, indicating that the virus will remain infectious during and after waste disposal. Survival time was shortest with elevated temperatures and a neutral pH.

However, as DEFRA confirmed, in the UK all birds culled in outbreaks are culled on the premises, transported under strict biosecurity measures and then incinerated, thus avoiding any risk from landfill leachate.