Nov 1
To date, researchers have not been able to develop a live animal test for scrapie. This means, the only 100% proof test for diagnosing scrapie in sheep or goats is the ELISA test, which is performed on the animal post-mortem. Producers often ask why a live test, like a blood test, has not yet been developed for scrapie. To answer this question, one must understand the nature of the disease.
Scrapie belongs to the group of diseases known as Transmissible Spongiform Encephalopathies (TSEs). TSEs occur in a number of different animals, for example, Bovine Spongiform Encephalopathy in cattle and Chronic Wasting Disease
in cervid.
The TSE diseases are extremely unique in the nature of the disease process, and although many of them have been around for a long time, it has only been since the early 1990s that the agent has been identified. The TSE agents are usually host specific and do not cause disease in another animal species.
The TSEs are transmissible (as the name suggests), however, they are neither a virus nor bacteria nor any other living form of transmissible agent that has been known to exist. The TSEs are caused by a protein-only agent, called a
prion protein.
All sheep have normal prion proteins in their body that are produced and broken down by the body’s normal systems. In this case, the animal is healthy. If a sheep picks up a scrapie prion protein (generally through ingestion), it acts as a template to cause normal prion proteins to mis-fold into a configuration that the body can no longer destroy. This leads to an accumulation of the scrapie prion protein in the animal.
It is this accumulation of the scrapie prion, in the brain, that leads to the death of brain cells and the clinical signs of scrapie, and then ultimately leads to the animal’s death.
There is no known treatment or prevention for the TSE diseases. All of the TSE prion proteins, including scrapie, are very difficult to isolate and although a lot of research has gone into developing a live animal blood test for TSE agents, there has not been one found to date.
Scientists are getting closer to developing a live animal test, and it is hoped that in the near future, they will succeed. Until they do, a 100% accurate scrapie diagnosis on an individual sheep or goat can only be confirmed through the
ELISA test.
