A national animal health goal in sight with a post-Halloween-twist? How perfect! Let’s take a closer look.
Scrapie is a fatal, degenerative neurologic disease that affects sheep and goats. It is one of a handful of diseases classified as a transmissible spongiform encephalopathy (TSE). TSE may ring a bell—these diseases are also known as prion diseases.
Prions are thought to be the causative agent but are still little understood. They aren’t living infectious organisms like bacteria or viruses (although there is debate as to whether viruses are technically alive!) but rather abnormal pathologic agents that seem to induce abnormal folding in normal cells. This leads to holes in the tissue, which is usually the brain.
In severe cases, the tissue resembles a sponge, hence the term “spongiform”. Mad cow disease, or bovine spongiform encephalopathy, is probably the most familiar prion disease. Chronic wasting disease of elk and deer is another prion disease.
The Scourge of Scrapie
But back to brains, specifically sheep and goat brains. Scrapie has impacted the U.S.’s small ruminant industry for several decades, first identified in a herd in 1947. The National Scrapie Eradication Program was developed by the USDA and its name says it all.
However, eradication is a tall order, and scrapie is a tricky disease.
For one, scrapie has a long incubation period. Animals typically show clinical signs two to five years after initial infection. Secondly, some animals can be infected and transmit the disease but don’t show signs themselves. Thirdly, diagnosing scrapie is done primarily by sampling the brain, which means the animal must be sacrificed (live animal sampling can be done via lymph node sampling, but this is also invasive).
These factors together make scrapie a challenge to identify and eradicate. To accomplish this, the USDA needs your help.
Clinical signs associated with scrapie are neurologic due to the damage within the central nervous system. Affected animals may progressively become nervous or aggressive. Some will intensely rub themselves on solid objects, as if they were extremely itchy. This is where the name “scrapie” comes from, since they rub so hard, they scrape and damage their wool and skin.
They may have tremors, press their heads on solid objects, or stare up at the sky, called “star-gazing.” Significant weight loss is also common.
There is no treatment for infected animals, so the progressive nature of these signs ends in the inability to move and subsequent death. The degenerative and untreatable nature of this disease illustrates why it’s important both for the health of the immediate flock and the small ruminant industry as a whole to eradicate it.
The current eradication program is based on identifying animals in order to ease tracing if needed and surveillance, mostly done at slaughter. Small ruminant farmers are strongly encouraged to participate in official identification and are required to do so if their animals cross state lines.
USDA’s Animal and Plant Health Inspection Service (APHIS) provides the official tags (there is a small fee). Age of the animal and its ultimate use (sale, slaughter, etc.) should go into the decision whether to participate in this identification program. A handy decision tree is available here.
Surveillance is the second big part of the program, and here’s the most recent USDA push. If you have an animal showing possible signs of scrapie or you have an adult sheep or goat that dies or is euthanized from these signs or unknown causes, contact your veterinarian. She can then contact your local APHIS Veterinary Services vet who will be able to provide supplies for official sample collecting.
The annual sampling goal set for the U.S. is 40,000 samples collected from sheep and goats 18 months of age or older to help find the final cases of scrapie and stamp out this disease.
There is a lot more to scrapie than what we’ve gone over here. Check out this excellent overview from USDA for more detailed information.