June 9, 2009 -- After an outbreak of the bird flu, most carcasses end up in landfills. There, according to a new study, the virus can survive for up to two years.
Landfills are designed to contain waste for far longer than that, so the practice is probably safe. Still, the new study suggests that waste managers might want to be particularly careful with how they dispose of infected birds.
"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. Other animals could be vectors. Landfill personnel could be potentially exposed."
Bird flu, also known as avian influenza, mainly infects birds, including chicken, ducks and turkeys. But human cases are becoming more common, and there are fears that future mutations could help the virus more readily spread from person to person, possibly leading to pandemics.
When birds on a farm come down with the disease, farmers usually kill the entire flock because that's the only known way to subdue an outbreak. So far, hundreds of millions of birds have been killed by the flu or by efforts to control it. During one outbreak on a Virginia farm in 2002, four million birds were tossed out.
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While options for disposal include composting, burning, and burying the bodies, carcasses most often end up in landfills. After that, no one has ever looked to see what happens.
To find out, Bartelt-Hunt and colleagues filled Petri dishes with leachate -- the liquid that drains from landfills. They added avian influenza to each dish. And they tested the mixtures at four different temperatures levels, three pH levels, and three levels of conductivity (to test for the presence of heavy metals).
After 60 days, the researchers were able to estimate how long the virus would remain infectious based on how quickly it was breaking down. At colder temperatures and neutral pH levels, the researchers reported in Environmental Science & Technology, the virus was likely to survive the longest -- sometimes for up to nearly two years.
"The assumption was that once it's in the landfill, there's no more question about whether it's infectious," Bartelt-Hunt said. "This is suggestive that carcasses will likely remain infectious when they're placed in a landfill and for a period of time after that."
The chances of bird flu spreading from landfills into the outside world remain slim, said David Stallknecht, an epidemiologist at the University of Georgia, Athens. The lab experiment was a simplified version of what happens inside landfills, he said. In the real world, plenty of factors are likely to deactivate viruses more quickly.
"I don't think there's any reason to be concerned whatsoever," Stallknecht said. "These are very conservative worst-case scenarios. To say that, even under the worst-case scenarios, this is a safe thing to do is really saying a lot."
It can't hurt to take precautions, Bartelt-Hunt said. There are currently no official guidelines for how to get rid of infected bird carcasses. The new work suggests that the bodies should get covered quickly to raise their temperature. It might also be worth making the landfill more acidic or basic to deactivate the virus as quickly as possible.
"In general, waste disposal is one of those things that's just: Out of sight, out of mind," Bartelt-Hunt said. "Once it gets there, people tend to think it's just gone and they don't have to worry about it ... It's hard to say if waste disposal is this huge unknown red flag out there, but I think having some consistent guidelines is important."
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