March 19, 2002

Questions and Answers About Scrapie From the National Scrapie Education Initiative

A. Yes, it is estimated that U.S. producers incur between $20-25 million annually. Only New Zealand and Australia are recognized as scrapie free, so they are currently the only nations that can freely sell breeding stock to producers in most other countries. Further, their lucrative markets are not available to U.S. producers. Losses can only increase in the future if the disease is allowed to spread.

Q. Can cattle get scrapie from contact with sheep?

A. No, scrapie from sheep and goats has not been shown to spread to cattle under natural conditions. Here in the U.S. scrapie isolates were injected into brains of cattle, it caused some spongiform changes, but did not cause the same lesion patterns as BSE and did not cause the same clinical signs. Oral inoculations did not cause clinical signs or lesions in cattle.

Q. Does scrapie affect human beings?

A.There is no evidence that people who consume sheep or goat meat or milk or who work with sheep and goats are at risk of contracting scrapie.

Q. How did the disease get its unusual name?

A. Individual sheep or goats that have scrapie will often rub on objects and scrape off their wool or hair.

Q. Do infected animals show any other clinical signs?

A. One or more of the following clinical signs of scrapie may be present in affected animals:

• Weight loss despite retention of appetite
• Behavioral changes
• Itching and rubbing
• Wool pulling
• Biting at legs or side
• Lip smacking
• Loss of coordination
• High-stepping gait of forelimbs
• Bunny-hop movement of rear legs
• Swaying of back end
• Increased sensitivity to noise & movement
• Tremor
• Down, unable to stand
• Weakness, difficulty getting up
• Death

Q. How widespread is scrapie in the USA?

A. Fortunately, it is relatively uncommon. Since it was first found in the United States in 1947, about 1,600 sheep and goats have been diagnosed with the disease. Only seven cases have been found in goats in the last 10 years. It is presumed that some flocks are infected but remain undetected due to the disease's long incubation period (typically two to five years) and difficulty in making a diagnosis, which is usually done with immunohistochemistry on brain tissue. As of August 1, 2001, there were 48 infected or source flocks in the U.S.

Q. Is there a live animal test?

A. A live animal test has been developed and is expected to be available later this year. The test uses a biopsy of lymphoid tissue from the third eyelid. Usually, topical anesthetic and restraint are used for the biopsy procedure, but in some cases the animal may be lightly sedated to collect the tissue. The new procedure will be used to test suspect and exposed animals for scrapie infection. It is expected to be a valuable tool in identifying and cleaning up infected herds/flocks.

Q. What causes scrapie?

A. An agent that is smaller than a virus causes scrapie. It is either a protein called a prion or it is another substance closely associated with the prion protein. Scientists still have a lot to learn about the scrapie agent and exactly how it works. It is known that the scrapie agent is extremely resistant to heat and to normal sterilization processes. It does not evoke any detectable immune response or inflammatory reactions in host animals. The incubation period is usually two to five years. Eventually, the scrapie agent attacks the brain, leaving holes in it much like swiss cheese or a sponge, hence the name spongiform encephalopathy.

Q. What is a prion?

A. A prion is a protein that is closely associated with scrapie infectivity and may be the causative agent. Normal cellular prion protein is found in all mammalian cells. The scrapie agent causes the normal cellular prion protein to be converted to an abnormal form called PrPsc that unlike cellular prion protein is not removed by the cell, causing it to build up or accumulate.

Q. Are some breeds of sheep more susceptible then others?

A. In this country, scrapie has been primarily reported in the Suffolk breed. However, it has been diagnosed in the United States in Suffolk, Hampshire, Cheviot, Southdown, Shropshire, Rambouillet, North Country Cheviot, Dorset, Finnsheep, Corriedale, Merino, Montadale, Columbia, Cotswold, Border Leicester, Texel and crossbreds. It is believed that most breeds and breed crosses of sheep and goats are susceptible to scrapie.

Q. What is the role of genetics in scrapie?

A. At present, it is generally accepted that scrapie is an infectious, contagious disease with genetics playing an influential role in susceptibility. U.S. sheep diagnosed with clinical scrapie have had a specific gene pattern. This pattern is known as QQ at the specific gene location codon 171. There are still many questions that must be answered before the role of genetics in relationship to scrapie susceptibility is fully understood and these are currently being researched.

Q. What has been done to control scrapie in the U.S. since it was first found in 1947?

A. From 1947 through 1992, regulations for dealing with scrapie-affected sheep in the U.S. underwent several changes in the classes of animals depopulated and the amount of indemnity paid. The number of reported cases of scrapie increased when the indemnity programs were instituted and/or the indemnity was increased. In 1992, the emphasis of the program changed from eradication to scrapie-free certification.

The Scrapie Flock Certification Program (SFCP) is a cooperative effort among producers, allied industry representatives, accredited veterinarians, state animal health officials, and USDA's Animal and Plant Health Inspection Service (APHIS). As of August 1, 2001, the program had 796 participating flocks.

For more information, visit www.animalagriculture.org/scrapie --
David Wahlberg
Director University News
North Dakota State University
(701) 231-8325