Deer disease seen as threat to humans: Experts compare CWD with resilient mad cow virus

Minnesota Rep. Rick Hansen, DFL-South St. Paul, right, shows leftover parts of a deer he killed — the hide, skeleton and hooves — before a hearing Thursday on chronic wasting disease at the Minnesota Capitol in St. Paul. Dave Orrick /  St. Paul Pioneer Press
Minnesota Rep. Rick Hansen, DFL-South St. Paul, right, shows leftover parts of a deer he killed — the hide, skeleton and hooves — before a hearing Thursday on chronic wasting disease at the Minnesota Capitol in St. Paul. Dave Orrick / St. Paul Pioneer PressDave Orrick / Pioneer Press

ST. PAUL — There is growing concern in the scientific and public health community that chronic wasting disease, which is killing deer in Minnesota, Wisconsin and elsewhere, could jump to people some day.

That unsettling news was featured in a hearing at the Minnesota Capitol Thursday, Feb. 7, where a number of experts from the University of Minnesota pressed upon lawmakers that the disease should be treated as a public health issue — a major expansion of its current scope as mostly a wildlife and hunting concern.

The issue is especially pressing for Minnesota, where wildlife officials are tracking the state’s largest outbreak of CWD to date in deer in the southeast portion of the state.

No person is known to have gotten sick from eating or handling a CWD-infected deer.

But scientists have always been wary of it because the disease is spread via extremely hardy protein cells, known as prions, making it similar to mad cow disease, which did jump from cows to people, where it is also fatal and without a cure.

Michael Osterholm, director for the University of Minnesota’s Center for Infectious Disease and Research Prevention who sat on a panel of experts tracking the emergence of mad cow disease, or BSE, decades ago, told lawmakers this:

“It is my best professional judgment based on my public health experience and the risk of BSE transmission to humans in the 1980s and 1990s and my extensive review and evaluation of laboratory research studies … that it is probable that human cases of CWD associated with the consumption of contaminated meat will be documented in the years ahead. It is possible that number of human cases will be substantial and will not be isolated events.”

He noted that for years, many in the public health and beef industry did not believe mad cow disease could infect people. In 1996, researchers confirmed that BSE (bovine spongiform encephalopathy) can infect people as variant known as Creutzfeldt-Jakob disease.

Why concern is growing

More than a year ago, Canadian researchers publicly presented initial findings that some primates — macaque monkeys — in a laboratory were fed CWD-infected meat and developed neurological disorders. The results have yet to be published in a peer-reviewed journal, but the findings sparked enough concern in Canada for the nation’s food safety agency to issue an advisory. The U.S. Centers for Disease Control and Prevention and the World Health Organization recommend against eating CWD-infected deer, but without anything conclusive, wildlife agencies throughout America say the decision is a personal choice, and some hunters do eat the meat.

Adding to the concern is this: The prions are nearly indestructible, capable of withstanding temperatures well above 1,000 degrees — and unlike viruses, CWD prions remain viable in the wild for years, sitting in the dirt, getting sucked up by plant roots and even just resting on inanimate objects.

Peter Larsen, an assistant professor at the University of Minnesota’s College of Veterinary Medicine, told lawmakers of a research project where a CWD-exposed rock was placed in a cage with hamsters — and they became infected.

“If I were to model contamination, the closest thing I can think of is it would be similar to modeling radioactive material,” Larsen said.

More questions than answers

One of the problems, Larsen and other experts said Thursday, is that much is unknown about CWD.

Among the questions:

• How much of a “dose” will infect?

• Where do deer actually contract it — saliva, feces, food, dirt?

• What happens to food-processing equipment that is exposed to a CWD-infected deer?

“We just don’t have tests for that,” said Jeremy Schefers, an assistant professor at the University of Minnesota’s Veterinary Diagnostic Laboratory — the only place in Minnesota where any CWD tests can be done. Those tests can only be done on brains, certain nodes and a few other parts of deer, and it takes days, Schefers said.

Portable testing proposed

Schefers and Larsen are part of a team proposing to develop a new testing device that can be used on live or dead animals and give results in minutes or hours, not days.

The team, which also includes nanotechnology experts, is asking lawmakers for $1.8 million to embark on the project.

Currently, wildlife officials believe only about 1 percent of the deer in Fillmore County are infected. However, in Wisconsin, where the disease has become endemic in many areas, infection rates are believed to have reached 35 percent in some deer populations.