From The National Academy of Science:
Scientists have found disease-causing proteins known as prions in the muscle tissue of deer in 11 states and two Canadian provinces. This is the first time prions have been found outside the brain and spinal cord of deer, and the discovery has raised concerns about human consumption of deer meat.
Prions are the abnormal form of particular proteins that naturally occur in mammals. When these proteins transform into prions, they cause rare, fatal brain diseases such as chronic wasting disease in deer and elk, mad cow disease in cattle, scrapie in sheep, and Creutzfeldt-Jakob disease in people. Deer and elk appear to transmit chronic wasting disease through excretions like saliva, although the details remain unclear; research in this area is ongoing. There is no evidence to date on whether prions in deer cause disease in humans or other mammals.