New Chronic Wasting Disease Findings Published

Sept. 3, 2003 -- A study by a University of Wyoming researcher and her Colorado colleague shows that deadly chronic wasting disease (CWD) in mule deer spreads in a "remarkably efficient" way from animal to animal. Their findings are being published in the Sept. 4 issue of Nature magazine, a science journal with subscribers throughout the world.

International CWD experts Elizabeth Williams of the UW Department of Veterinary Sciences and wildlife veterinarian Michael Miller of the Colorado Division of Wildlife contend in their article "Horizontal prion transmission in mule deer" that this "horizontal" route of transmission, as opposed to a transfer of the disease from mother to unborn fawn, likely contributes to epidemics affecting deer populations in parts of the United States.

"It is important to know as much as possible about transmission when attempting to control a disease because that information helps guide management approaches," says Williams, who is credited with first characterizing CWD in deer and elk as a graduate student about 25 years ago. "Knowing that maternal transmission doesn't seem to play a major role in CWD transmission is useful because control efforts won't be focused on does and their fawns."

The pair spent five years studying the spread of CWD within two cohorts of captive Colorado mule deer.

One group came from mothers likely suffering from CWD. The second population was born to apparently disease-free mothers but was mixed with the initial herd when the fawns were a few months old. All of the deer in the first cohort developed CWD, and 89 percent of the animals in the second group became infected.

"Fawns born to infected dams were as likely as those born to uninfected dams to contract CWD," Miller explains. "CWD transmits readily among unrelated deer during the course of an epidemic, and deer-to-deer (as opposed to strictly doe-to-fawn) transmission seems to be primarily responsible for perpetuating outbreaks," he adds.

Williams points out that "the mechanisms of transmission are probably similar, though amplified, in captivity compared to the situation in free-ranging mule deer. Thus it is reasonable to extrapolate from the captive studies to free-ranging deer that maternal transmission is unlikely to be very important."

Miller notes that "based on our findings, we need to focus on interrupting animal-to-animal transmission in its broadest sense. Focusing solely on maternal transmission will not be sufficient to control CWD."

Interest in CWD has grown steadily since the 1970s when Williams was training in pathology and began studying cases of the scrapie-like disease in wildlife. Media attention catapulted it into the headlines in the aftermath of the United Kingdom's diagnosis in the 1980s of another prion-caused illness in cattle herds called bovine spongiform encephalopathy (BSE), dubbed "mad cow" disease and eventually linked to a variant that afflicted humans. Williams says there is no evidence that humans are susceptible to CWD, a disease that attacks the central nervous systems of mule and white-tailed deer and elk, but advises hunters to be prudent and to refrain from shooting an animal that looks sick.

The next step in CWD research, the UW professor says, "is to try and figure out just exactly how the CWD agent gets from one deer to another deer." A new $2 million grant from the U.S. Department of Defense will help Williams, Miller and a team of colleagues from Wyoming and Colorado attempt to develop a technique to find infectious materials in the environment and in urine, feces and saliva that might spread the mysterious ailment. Studies are also underway to determine if the disease could affect cattle.

Miller says drawing attention to CWD research in a prestigious journal such as Nature is an honor and a reflection of growing scientific interest in prion diseases. "They seemed genuinely interested in the article," he says of the magazine's editors.

A spokesperson from Nature's London office says the journal, which covers the gamut of scientific news from astrophysics to ecology to neuroscience, looks for "exciting, groundbreaking research" to report. All articles go through a rigorous peer-review process before being considered for publication.

"I think it's fairly valuable for science in general to understand how diseases like CWD behave and how to manage them," says Miller. "We have some other research coming that will perhaps be equally well received."

Posted on Wednesday, September 03, 2003