Scrapie is a deadly disease that causes degeneration of the nervous systems of affected sheep and goats. The disease was first identified in 1732 and is believed to be caused by a prion. Fortunately, humans cannot get the disease from animals. However, animals can pass it to other animals, though it is not known how transmission occurs. Many researchers believe it is spread through urine or sexual fluids of the animals. Because of the lack of knowledge, the most common way to try and rid a flock of scrapie is to separate the infected animal or animals, though this sometimes does not work, since by the time symptoms appear, the disease may have already spread to the rest of the flock. As such, animals that can be affected by scrapie are required to be tested and tagged before they can be bred, sold, or used for meat. Work is also being done to try and breed animals that are genetically resistant to the disease.