A brain disease that affects sheep may be able to be spread to human beings. Scrapie is a disease in sheep that is similar to mad cow disease or bovine spongiform encephalopathy (BSE), a degenerative nerve disease.
Like BSE, it is caused by a protein called a prion that can be transmitted from one individual to another. Unlike BSE, which can spread to humans by eating infected beef, scrapie was not believed to be able to spread to humans. Usually, prion diseases do not jump from species to species.
In humans, similar forms of encephalopathy are called Creuzfeldt-Jakob disease (CJD), while BSE that has spread to humans is called variant Creuzfeldt-Jakob disease (vCJD). CJD is invariably fatal. It can run in families, but about 85% of cases are called sporadic because they occur in people with no known risk factors.
The finding was made by researchers at the National Institute for Agricultural Research (INRA) in Paris. They used mice, which have been used in the past to determine how BSE spread to humans as vCJD. When the sheep prions caused encephalopathy in these mice, they were indistinguishable from the prions that cause one form of CJD.
This finding suggests that there is a potential link between certain forms of CJD and animal prions. However, the researchers stress that all types of CJD are extremely rare and that even if transmission from sheep to humans is possible, it is not a serious public health risk.
Scrapie has been known to occur in sheep for centuries. It gets its name because sheep that have it compulsively scrape against trees and fences. Eventually, the sheep start to stagger, lose weight, and die.
In humans, CJD is very rare, affecting only about one person in one million worldwide and in the United States. Symptoms include memory loss, personality changes, and progressive dementia. Usually, people with CJD are in their sixties when symptoms start, however, vCJD has been diagnosed in younger individuals. Although several cases of vCJD were diagnosed in the United Kingdom in the early 2000s, only one case has been diagnosed since 2012.
