Download Scrapie Disease in Sheep: History, Prevention

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Scrapie Disease in Sheep: History, Prevention, and
Research
Since the late 1700s, scrapie has affected many sheep herds all over the world. Scrapie is
a disease that began in the late 1700s in Britain because of the high priority for wool production.
Britain faced a huge economic blow because of this fatal and spreading disease in sheep. Even
after all these years, scrapie can still be devastating to sheep farmers. Research has been a key
factor in prevention of this sheep disease. Knowing the signs and symptoms, causes, and
research based prevention of scrapie are important in healthy sheep herd management.
In the late 1700s, scrapie was a disease that sheep farmers did not understand and as a
consequence it spread to other countries. 1755 was the first recorded history of scrapie in
Britain. The British parliament discussed the economic effect of this disease and the need to do
something about it. Germany also faced the same effects in their sheep with many fatal deaths
occurring. A German literature in 1759 described scrapie affected animals by the following
description: they “lie down, bite at their feet and legs, rub their backs against posts, fail to thrive,
stop feeding and finally become lame. They drag themselves along, gradually become emaciated
and die” (Bradley and Brown). Many sheep herds during “the 18th and early 19th centuries saw a
rapid extension of scrapie” as a result of the practice of inbreeding to improve the quality of
wool (Bradley and Brown). Many farmers also practiced inbreeding to control the spread of
other diseases into their flocks. Unknown to the farmers, the practice of inbreeding made their
flocks more susceptible to the scrapie disease. The first case of scrapie in the United States was
diagnosed in 1947 in a Michigan flock of sheep. The owner of the flock had imported sheep from
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Britain through Canada for several years. And since this case through July 2001, scrapie has
been diagnosed in more than 1,000 flocks across the country (Scrapie Fact Sheet).
It is important for all sheep owners to understand scrapie in order to prevent the disease
in their flocks. Understanding the cause of scrapie is the first step in preventing the disease.
According to the Scrapie Fact Sheet, it says that scrapie is a fatal, degenerative disease affecting
the central nervous system of sheep. Scrapie is considered to be a transmissible spongiform
encephalopathy disease or TSE disease, which is also known as prion diseases. These are a
group of rare degenerative brain disorders characterized by tiny holes that give the brain a
"spongy" appearance (NINDS Transmissible Spongiform Encephalopathies Information). The
infectious agent in this disease is known as an infectious protein called a prion (Animal Health
and Laboratories Agency).
Scrapie is an infectious disease that is transmitted by the exposure to an infected sheep
and its environment. Scrapie is thought to be most commonly spread from the ewe, mother
sheep, to her offspring. The ewe’s placenta and placental fluids is the most likely cause for the
lamb to contract the disease. Scrapie can also be passed on by the poor sanitization of sheep pens
from infected sheep’s urine and feces. According to Animal Health and Veterinary Laboratories
Agency, scrapie is also spread by the mother’s milk and colostrum. Lastly, the genetic makeup of
the sheep affects their susceptibility to scrapie. Sheep with NSO1 type 1 (ARR/ARR) are
genetically resistant to classical scrapie (Animal Health and Laboratories Agency).
Knowing what signs and symptoms to look for is important in the detection of scrapie.
Many breeders do not know that their breeding stock is infected with the very few signs it shows.
According to the document Scrapie Fact Sheet, signs or effects of the disease usually appear two
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to five years after the animal is infected, but it may be longer. Some of the early signs are
changes in behavior, tremor (especially in the head and neck) and signs of itching evidenced by
rubbing itself on objects and biting of feet and limbs. Other signs are loss of coordination, weight
loss, lip smacking, and gait abnormalities including high stepping of the forelegs, hopping like a
rabbit, and swaying of its back end. The signs of scrapie vary from the individual animal and
develop very slowly. Due to the damage of nerves cells the sheep show these different kinds of
signs at varying times (Scrapie Fact Sheet). It is important to always try to observe for any
changes in sheep to determine if something is going wrong.
It is very challenging for farmers to prevent scrapie. Scrapie can be hard to detect
because of its long incubation period. There are also multiple ways to control the spread of
classical scrapie. Prompt cleaning and disinfecting of lambing areas and limiting the purchase of
replacement milk and colostrum from other flocks can help reduce the risk of scrapie (Animal
Health and Laboratories Agency). Another technology in the prevention of scrapie is known as
genotyping. According to Suffolk Sheep Society chairman Robyn Hulme “knowing the genotype
of a ewe can help breeders improve the scrapie resistance of their flock, while preserving
commercially important traits. Knowing the genotype of their ewes will enable flock masters to
greatly speed up the breeding of resistant flocks.” She also goes on to say that “mating less
resistant sheep to others with more resistant genotypes permits flock masters to preserve
commercially important characteristics of sheep with lesser genotypes” (Jonathan Long). In
other words, sheep genotyping could save a flock from any signs of scrapie. When purchasing
sheep, purchase replacement sheep from flocks that are genetically resistant or from flocks that
have had no scrapie outbreak in the last three years (Animal Health and Veterinary Laboratories
Agency).
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4th Hour
It has only been in recent years that testing has developed in the detection of scrapie in
live animals. According to the document by Tim Lundeen it states that in 1998, a team of
microbiologist developed the first practical test for diagnosing scrapie in live animals. Before
this time, the only way to confirm the disease was to examine a dead animal’s brain for spongy
pockets. The new test takes samples from a live sheep’s third eyelid. According to Bob Wagner,
the third eyelid testing takes advantage of the fact that prions tend to accumulate in lymph tissue.
The third eyelid of sheep contains two small lymph glands which can be removed without
permanent harm to the animal. Scrapie takes a long time to develop. Third eyelid testing is only
really good at detecting positives 10 to 14 months after infection. If a sheep was exposed to
scrapie at birth, it would test negative in the third eyelid test until it was nearly a yearling. In
other words, positives in the third eyelid test really are positive, but negatives don’t necessarily
mean negative.
The future of scrapie prevention is expected to look better for sheep. Scrapie research
efforts are currently focusing on developing a practical live animal test to diagnose infected
sheep before they show signs, investigating the ways scrapie is transmitted, isolating the scrapie
agent and its different strains, and identifying genes that control scrapie transmission (Scrapie
Fact Sheet). Researchers are working hard at identifying this agent and pinpointing how to
prevent this 250 year old sheep disease.
Overall, scrapie has been causing problems in sheep herds for 250 years. Scrapie is an
enemy in any sheep herd. Therefore, education to prevent scrapie is instrumental in controlling
the disease spread. Sheep farmers must be diligent in their disinfection, selection and purchase
of replacement stock, and incorporate the use of genotyping in their herds. Research is hopeful in
the development of new technology.
Hannah Sikkema
4th Hour