Brain Drain

In some parts of Colorado and Wyoming, four to six percent of deer (like these capitve animals) are infected with Chronic Wasting Disease. Is there a “mad cow” connection?
Photo courtesy of University of Wyoming

Since the mid 1990s, 35 Britons have died from the human form of BSE, which is known as new-variant CJD (nvCJD). nvCJD differs from the traditional form in some striking ways. CJD is usually seen in people over the age of 60, while nvCJD victims have been in their 20s and 30s or even younger. Patients with nvCJD have experienced convulsions, deafness and blindness—uncommon symptoms in classic CJD.

Until recently, CJD infected no more than one person per million annually in the U.S. But Doug McEwen’s case was one of six diagnosed in Utah during 1998, and in three of these cases the patients were 30 and under. Utah Department of Health Epidemiologist Gerri Dowdle believes that the increase in cases is a statistical anomaly. Ten percent of domestic CJD cases are known to be genetic, and one percent are acquired from certain surgical procedures. The rest are a mystery. “Keep in mind that statistics alone can be misleading,” Dowdle says. “Given the incubation period of the disease, we expect to see clusters occur about every 20 years.”

TSEs are unknown in U.S. cattle, but they have appeared in wild and captive-reared animals. Deer and elk in Utah, South Dakota and Nebraska have experienced a form of TSE called Chronic Wasting Disease (CWD), and some sections of Colorado and Wyoming have a four to six percent infection rate. Deer and elk game farms have also been infected, possibly through exposure to wild animal saliva at feeding stations. According to Tom Malmsbury, a scientist with the Colorado Department of Wildlife, “Three separate transmissibility studies are currently underway to determine if CWD can infect U.S. cattle.”

Until recently, CWD was an oddity noticed only by wildlife professionals. “Everybody is concerned now because of what happened in Britain,” says Tom Thorne, a veterinarian with the Wyoming Fish and Game Department. The fact that Doug McEwen was only 30 when he was diagnosed drew the attention of public health officials. When it was further discovered that he was an avid hunter and may have come into contact with CWD-infected deer, the concern became even greater. But an emphatic Dowdle points out, “There is absolutely no evidence of nvCJD occurring anywhere in the U.S.”

Michael Hansen, a researcher with Consumers Union, is concerned that people in the U.S. could acquire a new variant of CJD from animal hosts. “We already know that abnormal cow proteins will recruit [and later infect] normal human proteins,” says Hansen. “We need to be able to answer the simple question: ‘Can CWD from deer also infect humans?’ There seems to be a ‘don’t look, don’t find’ strategy, because this could be catastrophic to the meat industry.”

Numerous laboratory studies have demonstrated that TSE from one animal can infect an animal of a different species. BSE-infected cow brains fed to or injected into mink, hamsters, monkeys and other animals have caused unique versions of that disease in each animal. And Stauber believes that CJD occurs much more frequently than is currently estimated. “According to several studies, significant percentages of people who died of dementia diseases, as many as 13 percent examined post-mortem, have CJD,” he adds. “They’ve found that people who eat certain meats and brains have a higher chance of getting it.”

Epidemiological studies of people who developed CJD in the U.S. show that they eat more animal brains and pork than the general population. Handling raw meat or animal products, including manure and milk, are also considered risk factors for contracting CJD.

Scientists have only begun to understand the method by which TSEs spread. The infectious agent is a mutant protein, called a “prion,” which is smaller than any virus or bacteria. It cannot be killed by normal sterilization procedures, including chemicals or heat, and this makes it a particular problem for medical facilities. Many doctors are now using only disposable instruments for procedures on infected patients.

One method to curb the spread of TSEs is to limit the exposure of animals to infected meat. The importance of this was demonstrated in Britain where, in one decade, BSE spread from a few cows to thousands through the practice, now banned, of feeding them a supplement made from rendered animal byproducts (including bones, brains, organs and hooves).

Concern about the British outbreak lead to a 1997 U.S. ban on feeding parts of ruminants (cud-chewing animals) back to ruminants. But loopholes in the law still allow blood products from cows to be fed to calves, and for ruminant-fed pigs and chickens to be fed back to cows. The law also does not protect consumers from infected gelatin, fertilizers which may be used on vegetable crops, and animal-derived ingredients that are used in cosmetics.

A group that includes Michael Hansen and Tracie McEwen (Doug McEwen’s wife) have petitioned the Department of Health and Human Services and the Centers for Disease Control to have the loopholes in the feeding regulations closed, and to keep better track of CJD cases. Andrew Kimbrel, director of the Center for Food Safety and a petition signatory, says CJD “is a very mysterious disease that we just don’t know enough about. There is the possibility that we are on the brink of something terrifying.” If a cure arrives, it will come too late for Doug McEwen, who died March 28th, at the age of 30.