I’ve heard about mad cow disease, but what is mad deer disease?

I’ve heard about mad cow disease, but what is mad deer disease?

—Janet Bristol, Eugene, OR

“Mad deer disease” is a transmissible disease similar to mad cow disease, but it occurs in deer and elk instead of cattle. Called “spongiform encephalopathy,” but also known as “chronic wasting disease” (CWD), it was first discovered in 1967 on a Colorado wildlife research facility. It has since spread slowly through the mule deer, white-tailed deer and elk populations, mostly in western states. Mile Miller of the Colorado Division of Wildlife describes CWD as “an epidemic occurring in slow motion.”

The disease is found mostly in Colorado and Wyoming, where it infects about one percent of free-ranging deer, but about five percent of mule deer on game farms, due to the animals” closer proximity to one another which facilitates the spread of the disease. Infected animals have also been found on game farms in Nebraska, Montana, South Dakota and Oklahoma. Game farms sell meat and the velvet from antlers (marketed as a health supplement or aphrodisiac), or sometimes ship live animals to other states to bulk up their supply of hunting targets. Thus one farm with infected animals could potentially spread the disease far and wide.

Some health analysts fear that there could be a link between mad deer disease and Creutzfeldt-Jakob Disease (CJD), a similar type of spongiform encephalopathy that kills humans when brain proteins called “prions” deform, forcing other brain cells to degenerate along with them. Between 1997 and 2000, two deer hunters and a woman who regularly ate venison (deer meat) died from CJD. According to Dr. Ermias Belay of the U.S. Centers for Disease Control and Prevention, the three deaths raise concern because of the unusually young age of those infected. All three were under 30, while CJD usually only strikes people older than 45.

While scientists found no conclusive evidence linking the deaths to mad deer disease, they also couldn’t rule it out. And a National Institutes of Health report released last year warned that the transmission of spongiform encephalopathy between species is possible: “Infected tissues could be eaten by predators or enjoyed by aficionados of wild game. And carcasses could be rendered for feed that (by error) could find its way to cattle.”

Since 2002, hunters have donated some 200,000 deer and elk kills each fall to scientists looking to tabulate the prevalence of spongiform encephalopathy in American deer and elk populations in efforts to establish links to CJD. But the very states where mad-deer infection is highest also rely heavily on the sale of hunting licenses, making them loath to publicize the fact that eating venison could be dangerous. And indeed, even while scientists continue to look for clues, thousands of hunters and their families continue to eat venison with little if any concern about CJD.

CONTACTS: U.S. Centers for Disease Control and Prevention, (800) 311-3435, http://www.cdc.gov; National Institutes of Health: Prion Diseases, http://www.niaid.nih.gov/factsheets/priondis.htm; National Prion Disease Pathology Surveillance Center, (216) 368-0587, http://www.cjdsurveillance.com.