March 21, 2002 Isthmus (Madison, WI) by Brian McCombieLast month, the state Department of Natural Resources announced that three Wisconsin deer had tested positive for chronic wasting disease(CWD), an illness related to mad cow disease that can infect deer and elk. Hunters killed the deer last fall in the town of Vernon, in western Dane County, within two miles of each other.
While DNR and state health officials certainly weren't happy about finding it, their official statements, though generally reassuring, don't reveal that Wisconsin's deer herd could be all-but decimated by the disease. More importantly, these statements also tend to downplay the potential human health risks.
Chronic wasting disease is a Transmissible Spongiform Encephalopathy, or TSE, which alters proteins in the brain called prions, creating microscopic holes within brain cells. With mad cow, cattle shake with tremors and kick violently when touched. In deer, the symptoms include walking in circles, listlessness, and the progressive loss of weight. TSE's are always fatal.
Chronic wasting disease first began killing deer at a Colorado state wildlife facility in 1967, though the actual disease wasn't identified until 1980. By 1981, the first wild elk with wasting disease was found in Colorado. CWD then spread into northeastern Colorado and southwestern Wyoming, plus showed up at game farms in several, mostly western states in the 1990s.
Nebraska recorded its first wild deer with chronic wasting disease in 2000. By the following year, CWD was also in the wild in Saskatchewan (where 29 game farms were under quarantines between 2000 and 2001). The week before Wisconsin's announcement, South Dakota also reported its first case.
In the initial press release announcing the three infected deer, James Kazmierczak, an epidemiologist at the Department of Health and Family Services, cites the World Health Organization's (WHO) position--that "there is no scientific evidence that CWD can infect humans." Yet, as Kazmierczak also points out, WHO recommends no one eat meat or organs from an infected deer or elk.
An apparent contradiction?
Technically, Kazmierczak's correct: No scientific research has found an actual person infected by chronic wasting disease. However, notes Dr. Thomas Pringle, a molecular biologist who covered CWD issues for Sperling Biomedical Foundation in Oregon for five years, the research to determine human health risks from CWD is just about nil. So, in effect, a statement which cites no scientific evidence is actually one about a lack of scientific knowledge. No one's sure if CWD can infect people.
What information exists, though, is disturbing. In September 2000, the European Molecular Biology Organization published a study which found that deer prion materials infected with wasting disease were able to convert human prion materials in test tubes, albeit at very low rates. The study found that "CWD and [mad cow conversions happened] at about the same rate, in this proxy test, for humans," Pringle says. He also notes similar tests alerted British scientists that mad cow beef could potentially infect people.
"I can see why [Wisconsin health officials] wouldn't want to scare people who've already eaten venison," Pringle says. "But the best available science has to be the basis for public policy," and given the European study, "you can't in good conscience let people eat venison" from animals exposed to the disease.
Madison activist John Stauber agrees. Co-author of MAD COW U.S.A., Stauber says he's stopped eating Wisconsin venison, "until there is scientific proof that CWD does not transmit to people. Until that day, I consider CWD guilty until proven innocent of being a risk to humans."
Dr. Julie Langenberg heads the DNR's CWD testing, and thinks it extremely unlikely that CWD was transmitted nearly 1,000 miles through the wild from the western states, especially as it hasn't been found in areas in between. She's certain human intervention brought chronic wasting disease to Wisconsin, possibly through game farms.
As Isthmus first reported ("Stop The Madness," 7/14/00), Wisconsin game farms received approximately 350 elk from out-of-state farms with either known or suspected exposure to CWD. In 1999, the DNR began testing wild deer for CWD near these farms.
Many Wisconsin hunters, Langenberg notes, also hunt out west, and may have brought back a CWD-infected deer or elk. Once butchered, the remains could've been tossed into the wild, where deer--notorious bone chewers--gnawed on them. Bones, brains, and spinal cords of an infected deer or elk can be highly contaminated.
But however the disease arrived, events at one game farm suggest CWD could spread very quickly through Wisconsin's deer.
In 2000, infected elk were discovered at a game farm in northwestern Nebraska. The farm was quarantined, and the animals were killed and their brains examined for CWD. There were also 147 white-tailed deer kept in a separate enclosure. According to Bruce Morrison of Nebraska Game and Parks, by late February 2002, 83 of the CWD tests on the deer were completed, with 36 CWD positive or 43%, the highest infection rate ever found. (The previous high was 15% in wild deer in Larimer County, Colo., apparent center of CWD infection.) And wild deer within five miles of the Nebraska game farm are already testing at nearly a 7% rate of infection.
CWD experts, like the Colorado Department of Wildlife's Mike Miller, suspect that in a high density white-tail herd, with animals frequently in contact with each other, the disease could spread much faster than it has previously. Most wild CWD deer found in Colorado and Wyoming are mule deer, much less social animals than white-tails.
That's important, as it's believed that the disease passes between animals from casual contact like feeding together or noses touching. Plus, these mule deer are very dispersed, often at less than 10 animals per square mile.
Computer modeling by Miller estimates that starting with an extremely low rate of infection, CWD will essentially wipe out a deer herd in 50 years. "It's kind of slow starting out," Miller says, "but then it picks up speed." Yet, that modeling used mule deer, not Wisconsin's estimated 1.2 million white-tails, often found at densities of 40 to 50 animals per square mile. The real possibility exists, then, that CWD could tear through Wisconsin's herd faster than anything seen before.
Unfortunately, chronic wasting disease could already be well established here. Given the disease's long incubation period, Langenberg thinks two of the infected deer, which appeared healthy, likely had CWD for 18 to 24 months. The disease was apparently more advanced in the sickly third deer, which could have been a carrier even longer. Even the lower estimate means CWD was spreading in Wisconsin at least 18 months before these deer were killed last November. To get more test samples, the DNR began killing 500 deer in a ten mile radius around the town of Vernon. With these results, plus expanded CWD testing for road-killed and hunted deer, Langenberg hopes to understand CWD's current distribution.
But then what? There's no cure for chronic wasting disease. Colorado and Saskatchewan are giving deer hunters more licenses to lower deer populations, but there's no proof this will keep the disease from spreading. Pringle suspects there may be little anyone can do except watch this disease spread through Wisconsin and Midwestern deer.
The only real question might be how long it will take for the disease to reach the East Coast?