Scrapie is a fatal, degenerative disease affecting the central nervous system of sheep and goats that is very similar to BSE (mad cow disease), although it does not cause disease in humans, and has been present in the U.S. for over 50 years. Infected flocks that contain a high percentage of susceptible animals can experience significant production losses. In these flocks over a period of several years, the number of infected animals increases and the age at onset of clinical signs decreases making these flocks economically unviable. Animals sold from infected flocks spread scrapie to other flocks. The presence of scrapie in the U.S. also prevents the export of breeding stock, semen, and embryos to many other countries. Currently there is a national program underway to eradicate scrapie in the U.S. Signs of scrapie include: changes in behavior or temperament, scratching and rubbing, loss of coordination, weight loss, biting of feet and limbs, lip smacking, and gait abnormalities, including high-stepping of the forelegs, hopping like a rabbit, and swaying of the back end. Eventually the animal is unable to stand, and dies. Scrapie is a reportable disease, which means suspected cases must be reported to state and federal veterinary officials.
The Scrapie Program, as we know it, began November, 2001. So far, as of December 2005, 37 infected flocks have been found in Iowa. Of those, 10 have been depopulated, and 27 have completed, or are currently completing a genetic flock plan. Depopulation is generally only an option with small flocks, where the owner wishes to discontinue raising sheep.
Because the only reliable test to tell if an animal has scrapie or not is a brain test, performed after the animal is dead, we rely on genetics to eliminate scrapie from flocks. A blood DNA test can tell us which sheep could become infected with scrapie. The genetic flock plan involves drawing blood on all breeding sheep in the flock. Then all “QQ” sheep, the genotype most susceptible to scrapie, may be purchased by USDA, and the animals are euthanized and sampled for the presence of prions (scrapie infection). Following the completion of cleaning and disinfecting the lambing and post-parturient areas, the flock is placed on a post exposure monitoring plan for five years. During this time, animals exhibiting clinical signs will be sampled for scrapie. In some flocks, all “found deads” may also be sampled. Since all “QQ” ewes have been removed from the flock, the remaining ewes are “QR” and “RR”, which are generally resistant to scrapie. The use of “RR” rams is strongly encouraged, so as to prevent the production of “QQ” sheep, which makes a scrapie recurrence nearly impossible. The risk of scrapie transmission occurs only when susceptible (generally “QQ”) animals are exposed to the placenta and birth fluids of an infected ewe.
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