New technology destroys sheep that may have mad cow disease

April 2, 2001 Waste News by Cheryl A. McMullen

AMES, IOWA -- The 350 sheep destroyed for fear of exposure to a form of mad cow disease has forced the U.S. Department of Agriculture to look at new technology for disposal.

The USDA transported the sheep late last month to its National Veterinary Services Laboratories in Ames, Iowa, for euthanization by lethal injection last week, USDA spokesman Ed Curlett said. Tissue samples were collected >from the sheep for diagnostic testing.

The department will use a digester, a steel vat containing alkaline material, to break the carcasses down into liquid, which will be stored in tankers until tested to make sure the disease has been destroyed.

Once tested, an evaporator will pull the water out of the effluent leaving a powder form that likely will be incinerated on site, said Mark Muth, USDA biocontainment facilities manager in Laramie, Wyo. The digester reduces each sheep to a couple handfuls of powder.

The process breaks down any protein disease, Muth said.

Muth, who uses a digester to treat waste at a Wyoming USDA laboratory, suggested the technology for use at the Ames facility. Concerns about contamination were the overriding factor, he said.

The technology is more environmentally friendly than an incinerator and would succeed in destroying the disease in the carcasses where an autoclave likely would fail, he said. It could be two weeks before all of the sheep can be put through the digester, Curlett said.

The current situation in Europe highlights the USDA's role in safeguarding America's livestock from foreign animal diseases, the USDA said.

In 1996, the sheep were imported from Belgium and from the Netherlands. The herds were quarantined in 1998 when the USDA learned they likely were exposed to feed contaminated with bovine spongiform encephalopathy, a disease class that includes mad cow.

At the time, the state of Vermont imposed the quarantine that prohibited the slaughter or sale for breeding purposes.

Last July, several of the sheep tested positive for transmissible spongiform encephalopathy, characterized by a long incubation period and a 100 percent mortality rate, USDA officials said. Bovine spongiform encephalopathy in cattle and scrapie in sheep are two better known varieties of the class. There is no evidence that scrapie poses a risk to human health.

Based on current testing methods, there is no way to determine whether the sheep have scrapie or bovine spongiform encephalopathy.

The USDA issued a declaration of extraordinary emergency to acquire the sheep. The action was contested by the owners of the sheep but a federal district court judge ruled in favor of the USDA. The Second Circuit Court denied an appeal by the owners who requested a stay.

"While we understand this is a very difficult time for both flock owners, the removal of these sheep from Vermont's pastures concludes a determined effort by USDA to safeguard American agriculture against the threat posed by these animals," said Craig A. Reed, administrator of USDA's Animal and Plant Health Inspection Service.

The United States has never had a confirmed case of bovine spongiform encephalopathy.

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