Arkansas state officials announced Tuesday that Tyson Foods Inc. has begun the process of killing nearly 15,000 hens from a flock that tested positive for a strain of avian flu. In a 2005 "Explainer" column, Daniel Engber described how to dispose of birds infected with the disease. The article is reprinted below.
British government officials are planning to slaughter millions of hens, chickens, and turkeys if there's an outbreak of H5N1 bird flu on the island. In recent weeks, Romania has culled more than 50,000 domestic birds, and in 2004 the Canadian government destroyed more than 16 million chickens, turkeys, and ducks. How do these mass killings work?
In two stages: First you have to kill the birds, then you have to dispose of them. When the United Kingdom decided to kill off about 6 million cattle, sheep, and pigs to control an outbreak of foot-and-mouth disease in 2001, the military officer in charge of the operation described it as being more complicated than the Gulf War.
The World Health Organization has said that mass culls might be the best option for controlling the spread of bird flu, especially where vaccines are not available. To prevent the spread of the disease, authorities might order the destruction of every bird within a few miles of an infected bird. If there are multiple infections, culls can take place over large territories and include huge numbers of animals. (Governments usually reimburse bird owners for their losses.)
The World Organization for Animal Health says that culls of any kind should be performed under the direction of a veterinarian. The "cullers" themselves should wear coveralls or surgical gowns, an apron, rubber work gloves and boots, respirator masks, and goggles. They're also supposed to wash their hands frequently with soap and water.
The killing should take place away from public view, and the birds should be handled as little as possible. In general, infected birds should be killed first, followed by those birds that were closest to the infected birds, and then finishing up with the healthy birds. Whenever possible, younger birds should be killed before older ones, to preserve them from unnecessary stress.
Any of a number of methods can be used to cull a flock. Authorities in Canada used carbon dioxide, which kills birds by increasing the acidity of their cerebrospinal fluid. (Long-necked birds, like ducks, require more gas than the relatively short-necked chickens.) Cullers sealed up poultry houses with foam and duct tape and then pumped in the gas until they thought all the birds were unconscious or dead.
Birds can be killed with other kinds of gas, such as nitrogen or hydrogen cyanide, but CO2 tends to be the most common because it's cheap and easy to get. Another common technique hangs birds upside-down and then submerges their heads in an electrified water bath. For smaller operations, cullers might fire air guns into the skulls of the animals. Cullers can also wring birds' necks by hand or with a pair of burdizzo tongs. (OIE caveat: This technique may result in "operator fatigue.") Cullers may also decapitate birds with a guillotine or give them a lethal injection. Small birds can be killed by "maceration," which means they get tossed in something like a wood chipper. Newspaper reports say the culling operations in Asia (and a few other places, like Albania) have resorted to burying the birds alive after tossing them in plastic bags.
No matter how the birds are killed, their carcasses must be either buried, burned, composted, or rendered. Since bird flu can be transmitted from animal droppings, the culling teams are supposed to compost any feces or feces-contaminated soil they find as well.
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