September 3, 2002 New York Times by Sandra Blakeslee
As hunting season approaches, people in Wisconsin and the Rocky
Mountain states are increasingly worried about chronic wasting
disease, the variant of mad cow disease that afflicts deer and elk.
Scientists are fairly confident that no one in the United States has died from a human version of chronic wasting disease, but hunters are confused and frightened anyway. In Wisconsin in the past six months, 24 white tail deer have tested positive for the disease, and none of them looked sick. Not certain if venison frozen from last year's hunt is safe to eat, many families are throwing it away.
Surveys show that up to a third of the state's hunters plan to stay out of the woods this year, and many who do hunt will not be bringing their prey home. Economists estimate that the state may lose a third of the more than $1 billion that deer hunting brings to local businesses.
Similar fears are spreading in Colorado and Wyoming, where the disease has been endemic for decades and now spans a 20,000-square-mile area. Last week, the California Department of Fish and Game proposed a regulation to ban the importing of brains or spines from deer and elk killed by hunters.
Hunters who would once have called outfitters for advice on bagging an elk are today asking whether animals have tested positive for the disease, said Gary Wolfe, head of the Chronic Wasting Disease Alliance in Missoula, Mont.
At the same time, a fast-growing industry, the hunting of captive deer and elk, is under siege. By putting animals behind fences and raising them to grow large antlers, game farm owners guarantee hunters a trophy rack. They also sell the antlers, known as velvet Viagra, to lucrative Asian markets.
But chronic wasting disease appears to spread rapidly in captive elk and deer. One Nebraska ranch found chronic wasting disease in half its deer. A game farm in Colorado shipped 400 exposed elk to 15 states, including Wisconsin.
So hunters all over the country want to know what the disease is, whether it threatens people and how it can be stopped. But wildlife experts have no good answers.
Chronic wasting disease belongs to a family of disorders caused by aberrant proteins. Proteins are typically long molecules that must fold in particular ways if they are to function normally in the body and brain. Improperly folded proteins accumulate into gunky plaques and tangles in brain and body tissues. In chronic wasting disease, mad cow disease and other so-called transmissible spongiform encephalopathies, an errant protein called a prion misfolds.
Creutzfeldt-Jakob disease, a rare fatal disease that occurs in people, is a prion disorder that about 300 Americans develop each year. The version of mad cow disease that spread to people in Britain is a variant of Creutzfeldt-Jakob. Exactly how misfolded prions spread from one species to another is not yet known. But recent research shows that the prion, like other misfolding proteins, early on forms tiny toxic fibrils, or pores, that can literally poke holes in cells, a finding that may account for the spongy cavities seen in victims' brains.
Many researchers believe that a prion disease in sheep called scrapie was transmitted to cattle when British rendering plants that grind up animal wastes for use in feed lowered their processing temperatures to save fuel. From the early 1980's on, millions of head of cattle were fed high protein dregs from rendering plants, and thousands of them developed mad cow disease.
In 1996, the human version of mad cow disease, new variant Creutzfeldt-Jakob disease, was identified. Since then 135 people, mostly from Britain, have died from the new prion disease. No one knows whether the epidemic has peaked or if it will kill tens of thousands of people.
But if sheep spread the disease by eating the dropped placentas of infected ewes, and cows spread the disease by eating feed made from infected cows, how do deer and elk spread it? Wildlife officials do not know.
Animal experts in Wisconsin want to estimate how many of the state's 1.8 million white tail deer are infected. To do so, they will perform brain biopsies on 40,000 to 50,000 of the half-million deer that hunters are expected to kill in the hunting season, which begins this month and has been extended to January. Of these, 15,000 to 25,000 will come from a 374-square-mile area 30 miles west of Madison where all the infected animals have been found. All 25,000 deer in this so-called hot spot are to be eradicated.
Some experts are testing deer urine for abnormal prions. Dr. Valerius Geist, an emeritus professor of wildlife ecology at the University of Calgary, noted that male deer slurped urine from females during rutting season. "An actively rutting buck will have had in his mouth the fresh urine of about 100 does or more," Dr. Valerius said. "He is testing for when the female enters estrus, which is when mating begins."
Bull elk do not drink urine, Dr. Valerius said, but they spray themselves with it and females lick if off.
Deer also love to chew the bones of dead deer and elk, which could contain prions in dried marrow, Dr. Valerius said. Deer are known to nibble on fecal piles and, like elk, they slobber on each other and exchange drool.
Humans might also help spread the disease. For the last decade, landowners in Wisconsin's hot spot have been feeding deer mineral and protein supplements to produce big bucks with big antlers. If any of the feed contained prions from rendered roadkill deer -- an idea many experts find unlikely -- the disease could spread. Alternatively, the practice of attracting deer to feeding stations where they have a greater chance of exchanging body fluids may be a factor.
Once an infectious prion enters a deer, it is taken up by tonsils and is passed through the lymph, immune and nervous systems into the spinal cord and brain, replicating as it goes, said Dr. Elizabeth Williams, a veterinarian at the University of Wyoming and a leading expert on chronic wasting disease. The misfolded prions co-opt healthy prions, domino fashion. Wasting symptoms, like emaciation and lack of coordination, appear 14 to 30 months after exposure, she said.
There is no evidence that chronic wasting disease has naturally infected other species, including predators that feed on deer and elk, cattle or sheep that share natural habitat with them or hunters who love venison, Dr. Williams said. A species barrier, based on the fact that prions from one species can have a different enough shape to resist being co-opted by prions from another species, seems to protect many animals.
But that is not reassuring to a number of families whose loved ones ate venison and who later died of Creutzfeldt-Jakob disease, a natural human prion disease that usually appears in people over 65.
The Centers for Disease Control and Prevention investigated 13 cases of Creutzfeldt-Jakob in young people since 1979, said Dr. Ermias Belay, an investigator at the agency. Most cases can be explained by genetic or environmental factors having nothing to do with exposure to venison, Dr. Belay said. New variant Creutzfeldt-Jakob that came from cows has many distinct features that make the diagnosis unmistakable, he said. But younger Americans who died from the disease did not showcommon disease features. Finally, the incidence of Creutzfeldt-Jakob in states with chronic wasting disease is similar to that of states without the deer and elk disease, he said.
To halt the spread of chronic wasting disease, Wisconsin wildlife officials have banned the practice of feeding deer and plan to eradicate all deer in the hot spot. A computer model developed by Dr. John Cary, an ecologist at the University of Wisconsin, shows that if nothing is done, half of all deer in the core area will be infected in 10 years. In 25 years, all the animals will be dead, he said, and the disease will spread to the rest of the state.
"We've got a shot at putting the genie back in the bottle," said Dr. Tom Hauge, who directs the chronic wasting disease program of the Wisconsin Department of Natural Resources. "It means killing a lot of deer. But deer are not the enemy, the disease is."
This fall, Wisconsin officials will have to examine up to 50,000 deer brains and then dispose of animals that hunters do not want to take home. Of the 15,000 to 25,000 deer killed in the eradication zone, 450 to 750 are expected to have the wasting disease, said Doris Olander, who is in charge of disposal for the department. "At 140 pounds each," she said, "2.1 to 3.5 million pounds of deer will need to be buried or incinerated, beginning in October."
Dr. Hauge observed, "It's like you're standing on a highway with a Mack truck bearing down on you."