More than 230 sheep, which may have been exposed to mad cow disease agents, are being transported nonstop from two private farms in Vermont to the national veterinary laboratory in Ames for testing.

The 234 sheep will be euthanized at the United States Department of Agriculture National Veterinary Services Laboratories in Ames to determine if they are infected with some form of transmissible spongiform encephalopathy. The family of diseases includes bovine spongiform encephalopathy, more commonly known as mad cow disease, and scrapie, the form of the disease that affects sheep.

The first shipment of sheep was slated to arrive about 2:30 p.m. Thursday with a second shipment of 150 sheep scheduled to follow in the weeks ahead.

“We have done it before with other diseases with no impact to the farmers in Iowa,” said Ed Curlett, public affairs specialist for the USDA. “TSE is not something that can be spread from sheep in a truck to the surrounding countryside.”

Cases of scrapie do exist in the United States, but they seem to pose no health risks to humans, said Jim Dickson, professor of microbiology. There has not been a reported case of BSE in the United States, he said.

The USDA declared an extraordinary emergency when it announced in July 2000 that four sheep in Vermont tested positive for TSE out of a flock of 21. The department announced they planned to acquire two more related flocks of 355 sheep from the same area, an action contested by the sheeps’ owners. After several court cases, a federal district court judge ruled in favor of the USDA, Curlett said.

“The people that own these animals had to jump through hoops to get them [to the U.S.],” Dickson said.

The sheep came from Belgium and the Netherlands between April and December 1996 when the USDA allowed imports of sheep from different countries with certain restrictions, Curlett said.

“Belgium was free for that small period of time of disease concerns,” he said. “The sheep were imported legally.”

The sheep were monitored by the USDA for evidence of TSE under its voluntary scrapie eradication program. In 1998, they were placed under strict quarantine when the USDA learned from the European Union that the sheep could have been exposed to feed contaminated with BSE agents, Curlett said.

“Subsequent to their importation, [USDA] received information from the E.U. that their food system could have been contaminated with a BSE agent,” he said. “Quarantine was placed on these sheep at that time and we have been trying to buy them ever since.”

Although the sheep have been removed from the food market as of 1998, about 50 sheep went into the local market before the quarantine was imposed, Curlett said.

“Several sheep were sold locally here in Vermont,” he said. “None of them entered the animal food chain.”

TSE encompasses a vast spectrum of diseases including BSE, kuru, chronic wasting disease and scrapie. TSEs are characterized by their long incubation periods and spongiform appearance in the brain. It can be transmitted to both humans and animals through infected brain and spinal-cord tissue.

“The disease doesn’t spread readily from cow to cow or human to human,” said Hank Harris, professor of microbiology and veterinary diagnostic and production animal medicine. “It can only be acquired through actual consumption of meat that contains the agent.”

Currently, there is no treatment for the disease, and all cases are fatal. Victims show signs such as decreased motor movement and dementia, although many symptoms are slow to appear or do not appear at all, Dickson said.

“It is a slow-progressing illness in most cases,” he said. “Incubation periods may be 10 to 20 years.”

Although the source of the disease is still under debate, the prion hypothesis has been the most widely accepted, Dickson said.

“A prion is a protein that appears to be able to get similar proteins in the brain to reconfigure in ways that we don’t fully understand,” he said. “It changes the 3-D structure and results in the spongy appearance of the brain.”

Scrapie, a TSE affecting sheep, is characterized by gait abnormalities, loss of appetite and constant rubbing against objects. It has been around for more than 250 years and there has never been a documented case of scrapie transmitted to humans, Dickson said. The problem that resulted in the mad cow disease outbreak in the late 1980s could have had its roots in scrapie-infected sheep.

“The theory is that BSE in cattle may have started by scrapie-infected sheep being rendered and put in bovine feed,” Curlett said.

Because of the way the disease spreads, there is no chance animals can be infected with TSE from the Vermont sheep, Curlett said.

“There’s just no way,” he said.

TSE should not be confused with the recent epidemic of hoof-and-mouth disease in Europe, Dickson said. Hoof-and-mouth is caused by a virus that is easily transmitted among animals. It causes sores in the hoof and mouth regions, so the animal stops eating, but it is not lethal, he said.

“It’s like a mouth full of cold sores,” he said. “Personally, I don’t think it’s transmissible to humans.”

The sheep are being transported and tested at the National Veterinary Services Laboratories in Ames because all the expertise and equipment needed are in one spot, Curlett said.

“It is the best facility of its kind in the U.S. for this type of TSE work,” he said.

Although the results of preliminary testing on the sheep may be announced in a few months, in order to determine which type of TSE the sheep may have, a mouse bioassay must be used. This type of testing could take a couple of years at the very minimum, Curlett said.

“The mouse as a model shortens the testing period to a degree,” said Lloyd Anderson, distinguished professor of animal science. “It will not be a quick assay at all.”

The sheep must be euthanized to be tested for TSE agents. Brain tissue is then extracted and used as a testing agent.

“They have to inoculate the testing agent into the mouse brain to see if it will develop the agent of BSE. The agent ends up to be in little vacuoles in the brain area,” Anderson said.

After they are euthanized, the sheep carcasses will be disposed of in chemical incinerators, Curlett said.

“It will break down sheep completely into a couple of handfuls of powders,” he said. “It’s the same way that medical waste is disposed.”

The USDA is doing all it can to ensure the protection of the farmers in the Ames area, Curlett said.

“We are going to handle activities in a bio-secure matter,” he said. “Security is a precautionary measure to ensure the safety of the employees in case of unforeseen events that could happen around the lab. It’s a high-profile situation.”