Disease Basics
Scrapie is a fatal degenerative disease of the central nervous system. It afflicts sheep and goats. It is in the same family of diseases as bovine spongiform encephalopathy (BSE or Mad Cow Disease) in cattle and chronic wasting disease (CWD) in deer.
Scrapie is a condition in which sponge-like holes develop in the sheep and goat brain. Most scientists believe that scrapie is caused by prions — an abnormal form of a normal cell protein. It appears to spread most commonly from an infected, often normal looking ewe to her offspring and other lambs that come in contact with the placenta and placental fluids. The environment can become contaminated and remain so for years, serving as a source of infection to susceptible animals long after these materials have been removed. Although infection likely occurs at or shortly after birth, scrapie is a degenerative disease and signs usually develop 2 to 5 years later. Animals may live 6 months or longer after onset of signs, but there is no treatment, and death follows a progressive course of disease.
Susceptibility in sheep is linked to genetics, and genetic testing is available to aid in management of this disease. Genetic susceptibility in goats is not well understood, therefore all goats are considered susceptible when evaluating exposure risks for this species.
Prevention
The National Scrapie Eradication Program, a project of the USDA, was established to eradicate scrapie and have the United States declared scrapie-free by the World Organization for Animal Health by 2017. Achieving this goal will boost producers’ economic viability by increasing opportunities for exports, increasing value of animals, and decreasing production costs. Although there is no evidence to suggest scrapie is a human health concern, eradication can increase consumer confidence in a healthy food supply. The main tools in the program are animal identification to facilitate rapid identification of exposed animals and premises, surveillance testing among live animals and post-slaughter, and genetic-based flock cleanup plans.
The Scrapie Free Flock Certification Program provides producers with a framework for protecting their animals from scrapie and increasing economic opportunities for sales. Sheep and goat owners can choose to apply for participation in various categories, depending on their goals. Producers exporting live sheep/goats or embryos/semen will find participation to be especially useful and possibly required by receiving countries.
Clinical Signs of Illness
Clinical signs of scrapie are initially mild and progress in severity over weeks to months. Signs vary widely among individuals and may include:
- Subtle changes in behavior and temperament, especially in early stages
- Scratching and rubbing against fixed objects
- Loss of coordination
- Abnormal gaits, including high-stepping with the forelegs, hopping, and swaying the back end
- Weakness
- Weight loss
- Biting feet and limbs
- Lip smacking
Infected animals may appear normal at rest, but if startled or stressed, tremble or fall down as if in a convulsion.
Diagnosis/Treatment
Veterinarians can diagnose scrapie in live animals by biopsy of lymph tissues from the inside of the third eyelid or rectal mucosa. Most often, however, it is diagnosed by examining brain tissue under a microscope after death.
Human Health
There is no evidence of a human health risk.