Attending the House of Delegates session as a member of the HOD advisory panel, FDA-CVM director, Dr. Stephen F. Sundlof on July 21 updated delegates on what is known so far about the Vermont sheep flocks confirmed positive July 10 for a transmissible spongiform encephalopathy. He reported what actions are under way and answered delegates' questions.
Calling it a "fairly complicated issue," Dr. Sundlof said it is not known whether the TSE is "a normal scrapie" or might be bovine spongiform encephalopathy.
"In cattle, the BSE agent is pretty much isolated to brain, spinal cord, and lymphatic tissue. Scrapie in sheep is very much different," Dr. Sundlof noted. "It distributes to a number of different tissues outside the brain, spinal cord, and lymphatic tissue, and whether it will distribute into the milk is unknown. If BSE is now in sheep, will that BSE prion behave like a regular scrapie prion and be distributed to other tissues, including milk? CDC has basically said this is highly theoretical, but it could happen."
Determining which type of TSE has infected the sheep will take two years, he said, because the organism has to be passaged through mice.
This really is a USDA-APHIS issue, he noted, but the USDA is working with other federal agencies and the state of Vermont to identify any associated human health concerns.
On July 14 the USDA announced it would acquire 376 sheep from three Vermont flocks after four sheep were confirmed positive for the TSE. The agency was purchasing one flock of 21 sheep and issued an order to seize two other flocks of 355 sheep. The USDA will destroy the sheep, most of them East Friesian milk sheep, to prevent possible contamination of other livestock.
A court hearing was scheduled for July 21 at which at least one and probably two of the three farms were filing suit to enjoin APHIS from seizing their flocks.
When the original sheep, imported from Belgium and the Netherlands, entered this country in 1996, they were placed under limited federal restrictions as part of the USDA's voluntary scrapie eradication efforts. In 1998, the USDA learned it was likely that European sheep had been exposed to feed contaminated with BSE. At the USDA's request, Vermont imposed a quarantine on the flocks, prohibiting their slaughter or sale for breeding purposes. Since 1996 the USDA has been actively monitoring these flocks for any evidence of TSE.
Milk from the sheep was sold and used to produce cheese that also was sold. None of the original imported sheep was slaughtered for human consumption. Prior to imposition of the quarantine and detection of TSE, however, some offspring were slaughtered for human consumption.
"One issue is that in the European [Community], where BSE is endemic, there's a question as to whether BSE has transferred into sheep flocks in Europe. Nobody knows for sure whether sheep in Europe naturally have acquired the BSE prion. Experimentally they have been able to cause BSE in sheep. ... It is not unreasonable to think [sheep may have acquired BSE naturally]," Dr. Sundlof said.
Another issue is whether cheese from the sheep is safe, one of the issues discussed at a Department of Health and Human Services meeting July 21. The World Health Organization has determined that with cattle, cheese is safe, Dr. Sundlof said.
A delegate asked whether any of the suspect sheep had been sold. Dr. Sundlof said some had, but their destinations were known. Precautions are being taken that the sheep not be rendered and used in cattle feed. He said that a number of lambs had been slaughtered for food, and the rendering plant where they were sent is currently undergoing inspection to ensure that none of the animals will be used in bonemeal.
The American Association of Small Ruminant Practitioners, meeting in conjunction with the AVMA in Salt Lake City, was also discussing the TSE developments.