Ask the Doctors by Eve Glazier, M.D. and Elizabeth Ko, M.D

Chronic Wasting Disease on the Rise Among Deer in the U.S.

Dear Doctor: My dad and brothers are hunters, so there's always deer meat in the freezer and it's often on the menu. But I'm hearing that it's now linked to a brain disease. Should we be worried?

Dear Reader: You're referring to chronic wasting disease, also known as CWD, which has now been found in deer herds in at least 23 states. It has also been identified in moose, elk and reindeer, and is a becoming a problem in Canada, Norway and South Korea as well.

Chronic wasting disease is a progressive disease that affects the functioning of the brain and spinal cord of the infected animals, and invariably leads to their death. Although it is highly contagious among animals -- the disease continues to spread in wild deer herds and fenced-in hunting ranches -- there are no known cases of transmission to humans at this time.

CWD is part of a family of disorders known as prion disease. If that sounds familiar, it's because prions play a leading role in mad cow disease. The disease created an uproar when it was identified in Great Britain, Europe and the United States in the late 1980s through the early 2000s. Mad cow caused several hundred deaths in humans, mostly in Great Britain, and resulted in 4.5 million cows being destroyed.

Although prions are normal proteins found in the brains and nervous systems of most animals, including mammals, reptiles and birds, the prions involved in the disease process behave abnormally. They start a chain reaction among the normal proteins in the brain, causing them to fold and bend and become deformed. This prevents the proteins from fulfilling their specific biological purposes, and ultimately results in the characteristic spongy appearance in the brain tissues of the infected animal. In CWD, prions cause numerous small holes to develop in the brains of infected deer, which affect the deer's behavior and lead to death.

Symptoms in infected deer include tremors, loss of coordination, weight loss and wasting, a lack of awareness of the surroundings, an uncharacteristic loss of fear of humans, and increased thirst, urination and salivation. The incubation period of CWD is quite long, averaging from 18 to 24 months. That means an animal can be infected with the disease but not show any ill effects. CWD is transmitted among herds of deer through normal contact, like touching noses, licking, mating and giving birth. In addition, soil contaminated by the urine, feces or carcass of an affected animal remains a vector of infection for more than a decade.

CWD was first identified in the late 1960s, but as we mentioned earlier, there are no known instances of transmission to humans. However, because mad cow made the leap to humans, scientists are now investigating whether the same thing can happen with CWD. Wildlife officials in Colorado and other heavily affected states are urging hunters to bring their deer in for testing before consumption. This involves an analysis of tissues from the brain and lymph nodes. The agency that issued your hunting permit will have complete information.

(Send your questions to, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)