This video shows the behavior of some sheep suffering from scrapie.
History of Scrapie
Scrapie has been a recognized disease for more then 250 years (NDA, 2004). In 18th century Britain during wool was one of the most important commercial products and British Parliament became quickly concerned about the economic effects of this mysterious disease. In 1947, scrapie was introduced to the United States, through a flock imported to Michigan from Great Britain. In the United States, scrapie has primarily been reported in the 'Suffolk' breed. It also has been diagnosed in a Border Leicester, Cheviots, Corriedales, Dorsets, and a number of other crossbreeds. The reported number of infected sheep in the United States ranged from 198 to 307 (NDA, 2004).
Scrapie, like kuru is a prion disease or transmissible spongiform encephalopathy (TSE). After a sheep is infected with a prion disease, the infectious agent typically enters the lymphatic system and travels to lymph nodes. After 'attacking' the lymphatic system, the prions are eventually go to the brain, where they form 'holes' in brain tissue.
Signs of scrapie vary incredibly among animals and the disease develops very slowly. Sheep (and goats) can be infected at a very young age, but may not show symptoms of disease until two to six years of age (NDA, 2004). The prions attack nerve cells and because of this, affected animals show very observable behavioral changes: tremor, rubbing of wool, poor locomotor coordination. The symptoms progress and eventually lead to death (USDA, 2010). Other symptoms may include:
~Weight loss, despite normal appetite
~Excessive itching and rubbing
~Wool pulling or biting
~Loss of coordination
~Startling at sudden noise or movement
~High-stepping gait (front legs)
~Bunny-hop movement (rear legs)
~Swaying of back-end
~Inability to stand.
Diagnosing scrapie typically involves observing symptoms for a long duration, and eventual submission of brain tissues from an affected animal. The presence of prions in a microscopic section of brain tissue is the only method to be certain that sheep are infected with scrapie. A test of lymph tissue contained in the third-eyelid of sheep can be performed by a regulatory veterinarian in some instances, but this test is not used for routine scrapie diagnosis. If a sheep is suspected of having scrapie, the responsible individual should contact their local veterinarian for a diagnosis (USDA, 2010).
The United States Department of Agriculture (USDA) Animal Plant Health Inspection Service (APHIS) launched a new Scrapie Eradication Program in November of 2002. All states agreed to consistently upholding standards with the program so that producers could transport sheep between states. It is estimated that scrapie costs American sheep producers $25 million annually (USDA, 2010). USDA has funds that are available for the clean up of infected flocks. This clean up includes the costs associated with DNA testing, and the purchase of infected and susceptible sheep at fair market value (USDA, 2010).
Other aspects of the eradication program include identification of sheep and goats with official USDA scrapie tags in breeding sheep and sheep older than 18 months at the time of sale, purebred goats and goats that have resided with sheep, and all unaltered sheep and goats for exhibition.
Producers must also keep good records including names and addresses of purchases and sales of sheep from the flock. When participating in the program, flock owners must report any scrapie suspects immediately to animal health official, officially identify all sheep over one year of age or when a change of ownership occurs (except slaughter), maintain adequate records including all sales, purchases, births and deaths for a minimum of five years, agree to an annual inspection by regulatory health officials for symptoms of scrapie, record completeness, and verifying identification of the flock and purchase replacement-breeding animals from flocks of equal or higher status.
A list of flocks enrolled in the certification program and their status is available on the USDA web site.