An Oregon sheep found to be infected with scrapie earlier this year was the only animal in its flock to have the disease, authorities say.
Tests recently confirmed that none of the other 300 sheep that were predisposed to the central nervous system disease were actually afflicted by it, according to USDA.
“What we have is one sheep. We started with one sheep and we still have one sheep. It’s not an outbreak,” said Oregon State Veterinarian Brad LeaMaster.
The agency’s Animal and Plant Health Inspection Service, or APHIS, is now conducting a “trace-back and trace-forward” investigation to determine if any other flocks were exposed to scrapie, said spokesperson Lyndsay Cole.
Routine testing of slaughtered sheep uncovered the scrapie-infected sheep in June, and the USDA notified the state and the animal’s Douglas County owners in August, said LeaMaster.
About 300 sheep within that flock tested positive for genetic susceptibility to the disease, he said. The owner agreed to have them euthanized and their brains examined for the disease.
In mid-November, those results showed that the infected sheep was an isolated case within the flock, Cole said.
“Now begins the epidemiology of where it came from,” said LeaMaster.
Scrapie is a degenerative disease in the same category of illnesses as bovine spongiform encephalopathy, or mad cow disease, but there’s no evidence that it can impact human health, according to APHIS.
“It’s not a food safety concern,” said Cole.
Even so, the USDA has been aggressively trying to eradicate the disease due to its negative effects on export markets, and over the past decade its prevalence has decrease more than 90 percent, LeaMaster said.
The last case in Oregon was detected in 2008, he said. “The smaller the prevalence, the harder it is going to be to find it in the flocks out there.”
In the past year, APHIS has identified 18 positive scrapie cases in the U.S. — 15 in sheep and 3 in goats — across eight states and one unknown location, according to an agency report.
The disease causes behavioral changes in afflicted animals due to nerve damage, including tremors, convulsions and lack of coordination. Sick animals often rub themselves against other objects and lose weight.
Symptoms may not appear until two to five years after an animal is infected, but once they do it will usually die within six months.
Transmission of the disease is thought to occur from a ewe to her offspring or through contact with an infected placenta.
“The way it moves around is at birthing time,” LeaMaster said. “This one moves around at glacial speed.”