Scrapie; A disease caused by a prion related to BSE and CWD of Elk and Deer

Journal of the American Veterinary Medical Association ^ | May 1, 2002 | Susan C. Kahler

[vetvetdoug]

Following is a synopsis of the current knowledge about scrapie and resource information.
Causative agent, transmission:Scrapie is a tranmissable spongiform encephalopathy widely thought to be caused by a misfolded prion protein that accumulates in the brain. However, there are also two other theories--that the agent is a virus with unusual characteristics, or a virino, a small, noncoding regulatory nucleic acid coated with a host-derived protective protein. According to Dr. Katherine O'Rourke, a USDA research microbiologist in Pullman, Washington, "Infection is believed to be caused by ingestion of that misfolded protein (through the placenta and placental fluids) by the lamb or other adults nearby. The protein bumps into the normal folded protein in the gut and is amplified-that is, the bad proteins make the good ones go bad. Then it's thought to be transported to the brain by the Vagus nerve."
Destroying the Infectious Agent:The prion is resistant to heat and most sterilization processes. Bleach is effective in decreasing detectable amounts of the TSE agent.
Incubation Period:Typically two to five years, but according to Dr. Diane Sutton, national scrapie program coordinator, six to nine years for animals exposed after weaning. For this reason, it is presumed that some flocks are infected but remain undetected.
Diagnosis:Usually the disease is diagnosed with immunohistochemistry on brain tissue. A live animal test has been developed and is currently being used in infected and exposed flocks by staff of the Department of Agriculture's Animal and Plant Health Inspection Service. This test uses a biopsy of lymphoid tissue from the third eyelid. Of 100 sheep, Dr. O'Rourke said that 85% have third-eyelid tissue suitable for biopsy. If all 85 specimens were positive, 88 percent would show positive on this test. She said that a sheep with a positive test result will die within 28 months.
Vaccine:There is no vaccine
Treatment:There is no successful treatment
Breeds Involved:In the United States, scrapie has been reported primarily in the Suffolk breed, but it has also been diagnosed in Hampshire, Cheviot, Southdown, Shropshire, Rambouillet, North Country, Dorset, Finnsheep, Corriedale, Merino, Montadale, Columbia, Cotswold, Broder Leicester, Texel, and crossbreds. Although scrapie has been most common in the blackfaced breeds, it is also being diagnosed in whitefaced Columbia sheep. It is believed that most breeds and breed crosses of sheep and goats are susceptible.
Goats:Only nine cases have been found in goats in the past 12 years. When cases do occur, they are usually caused by ingestion of the placenta or placental fluids of infected sheep or cutaneous contact through abraded skin. Goats are included in the eradication program so that infected ones are tracable and an indemnity can be paid to affeted goat producers.
Prevalence:As of January 31, 2002, there were 61 infected or source flocks in the United States. It is presumed that some flocks are infected but remain undetected because of the long incubation period and the difficulty in making a diagnosis.
Scrapie-free countries:The United States recognizes only two countries as being free of scrapie-Australia and New Zealand.
Clinical Signs of scrapie: One or more of the following clinical signs may be present in affected animals. It is important to note that not all sheep or goats show all the signs of scrapie. Sometimes these signs can be so subtle that they are missed or misdiagnosed until they have progressed. Weight loss, despite retention of appetite, behavioral changes, itching and rubbing, wool pulling, biting at limbs or side, bunny-hop movement of rear limbs, increased sensitivity to noise and movement, tremor, down and unable to stand.

[vetvetdoug]

There was another thread on Chronic Wasting Disease of Elk and Deer and the transmisson of the disease in these by a prion was unclear. Considering what is known about scrapie, the CWD of Elk and Deer must follow the same infectious route. Just last month, researchers in Great Britain were unable to transmit Bovine Spongiform Encephalopathy by the vertical route. This means that cows do not spread BSE to the calves in the uterus. From what researchers know right now, CWD of Deer and Elk and Scrapie are transmitted by the contamination of placenta and placental fluids to the susceptible. BSE or "Mad Cow" is transmitted by the ingestion of neural tissue from an infected individual.

[martin_fierro]

Whatever it is, I don't want it.