June 8, 2002 Wisconsin State Journal by Ron SeelyThough there is little scientific evidence that chronic wasting disease can cause illness in humans, scientists who study the disease remain unsettled because a similar disease in livestock in England, mad cow disease, did leap the species boundary and infect people.
Now, with chronic wasting disease diagnosed in 18 Wisconsin deer, many wonder whether the disease might eventually find its way into people. Some researchers are calling for more surveillance of Creutzfeldt-Jakob disease, the form of the illness that gets passed to people. Currently, despite the spread of CWD, the Centers for Disease Control and Prevention does not require reporting of Creutzfeldt-Jakob cases.
Even the field's most knowledgeable researchers are hedging on potential human health impacts. Judd Aiken, a UW-Madison expert on CWD, worries about the possibility of CWD-tainted venison passing some form of Creutzfeldt-Jakob disease to humans.
"Right now there is no evidence that CWD has been transmitted to humans to cause Creutzfeldt-Jakob," Aiken said. "And I think one can make a lot of rational arguments against that happening. But would I recommend anyone consuming venison from the endemic area? No, I would not. And I wasn't making that statement earlier."
It is a question of pressing importance here in Wisconsin, where thousands of freezers contain packages of venison from last year's hunt. The possibility of the disease jumping to other species is important, also, to farmers who wonder if the disease can pass from deer to their livestock.
Hunters and others who consume venison get little in the way of assurances from the state Department of Natural Resources. DNR Secretary Darrell Bazzell has said several times recently that the agency cannot guarantee the safety of venison.
Yet others continue to emphasize that no research has connected the deer disease to human illness. On its Internet site, for example, the Wisconsin Department of Health and Family Services has posted a mostly reassuring statement about any links between CWD and new variant CJD, or vCJD, the human version of the disease that researchers have traced to mad cow disease.
"CWD," the statement reads, "has occurred in the USA for at least four decades and there have been no confirmed cases of vCJD detected in this country. Furthermore, the incidence of CJD in residents of Wyoming and Colorado where CWD is endemic is no higher than in states where CWD does not occur. The World Health Organization and the U.S. Centers for Disease Control and Prevention has found no scientific evidence that CWD can infect humans."
Hanging over all of this like a cloud, however, is the outbreak of mad cow disease, or bovine spongiform encephalopathy, in England in the mid-1980s. Despite repeated assurances that the disease was limited to livestock, more than 130 people have died of new variant Creutzfeldt-Jakob disease. Aiken said there is little doubt of the connection between mad cow disease and vCJD.
John Stauber, a Madison writer who wrote a book on the possibility of mad cow disease in the United States, is convinced we are making the same mistakes in this country that were made in England. There, he said, officials assured consumers that beef was safe even though researchers showed mad cow could infect other species, such as cats and mice and monkeys. Such assurances were still being provided, Stauber writes in "Mad Cow U.S.A.," even after medical researchers discovered a new strain of CJD that had killed eight young people and had striking similarities to mad cow disease. All of the victims had eaten tainted beef, investigations showed.
"They didn't act quickly enough," said Stauber. "They gave false public health assurances."
Infecting another species
Researchers who are studying the "species barrier" say that experiments so far show that CWD-infected proteins, or prions, injected directly into the brains of livestock and other species do not convert healthy proteins into diseased proteins at a high enough rate to cause concern.
Beth Williams, the researcher at the University of Wyoming who first identified CWD in deer and elk as a transmissable spongiform encephalopathy -- a protein disease similar to mad cow -- has infected a number of species with CWD. In one experiment with livestock, Williams and other researchers injected CWD prions into the animals' brains. Three of the 13 animals developed the protein disease within 24 to 27 months.
Five years ago, Williams also orally administered CWD to livestock, which she considered a more realistic and useful test because the disease is likely transmitted among deer through nose-to-nose contact. None of those animals have yet developed CWD, although the incubation period for the illness can be up to six years.
But even researchers such as Williams say they would be more comfortable if CWD prions had not shown up at all in other species into which the disease was injected.
In one experiment, CWD infected human tissue in a Petri dish. Byron Caughey, a researcher at Rocky Mountain Laboratories in Hamilton, Mont., injected human tissue in the lab with CWD and the infected prions did change healthy human proteins into diseased proteins. Williams cautioned that such an experiment does not account for any of the barriers that might keep humans from contracting the disease. It appears, she pointed out, that some people simply don't get the disease. Of the millions of people who have eaten tainted beef in England, she said, only 130 have contracted the new variant of CJD believed to be caused by mad cow disease.
Risk of transmission
But Dr. Thomas Pringle, another well-known protein disease researcher, said Caughey's work was evidence that there is a definite risk of transmission.
Given all of this uncertainty, some are calling for more extensive surveillance of CJD cases in the United States, and especially in states such as Wisconsin.
Now, just as was true in the 1990s in England, there have been a number of cases in the United States of CJD occurring in people much younger than those who normally contract the illness. The new version of the disease that showed up in England is killing people in their teens and 20s while the sporadic, or classic, version of the disease strikes people 60 and older. So far, investigations by agencies such as the Centers for Disease Control and Prevention have found no connection between cases of CJD in young people in the United States and chronic wasting disease.
In the handful of cases that have been investigated, the cause of death has been found to be classic CJD. The sporadic version of the disease is thought to arise spontaneously as opposed to new variant CJD, which is caused by eating meat tainted with mad cow disease.
Among the cases that have surfaced:
* Three deer hunters under 30 who died of CJD between 1997 and 2000. The hunters were from Maine, Oklahoma and Utah and a study published in the Archives of Neurology last October found no connection to CWD.
* A 39-year-old Minnesota man who died six years ago and might have eaten venison from Wisconsin deer. Dr. Richard Johnson, a Johns Hopkins University neurologist, said the case merits more study.
* Two young men, ages 26 and 28, who died last fall in the same Michigan hospital of the brain wasting disease. A study by the CDC found no connection to CWD and one of the men may have had a family history of CJD.
'A lot of unknowns'
Some think we aren't looking hard enough for the disease or that we might be looking for the wrong thing.
Despite the continuing spread of chronic wasting disease across the United States and the tentative links between the disease in other animals and possibly humans, the CDC does not require reporting of CJD cases.
Lawrence Schoenberger, a medical epidemiologist who heads CJD surveillance for the CDC, the question of whether to make the disease reportable is left to individual states. He added that 12 states require reporting of the illness. He also said the agency is looking more closely at the disease in young people and would like to see more autopsy reports from such cases.
Schoenberger said there are a number of problems with making the disease reportable. It is often not diagnosed correctly, he said, or sometimes not diagnosed at all.
"There are a lot of unknowns," Schoenberger said. "And it is precisely because there are a lot of unknowns that the Centers for Disease Control doesn't go out to Wisconsin and tell people that there is nothing to worry about. Because that's what they did in Britain."
Linda Glaser of the Wisconsin Division of Public Health said CJD is not a reportable disease in the state. She added, however, that the outbreak of CWD in the state's wild deer herd has prompted officials to consider increasing surveillance of the disease.
The UW-Madison's Aiken warned that if CWD were to pass to humans it would probably do so in a form that is unique to protein disease in white-tail deer and that hasn't been seen before. That's all the more reason, he added, to make the disease reportable and to be vigilant about keeping track of CJD cases. After all, prior to its appearance in England in the wake of the mad cow disease outbreak, nobody had ever seen new variant CJD.
And even some physicians who are aware of cases of CJD among young people in the United States wonder whether a new form of the disease related to CWD might be emerging.
Johnson, of Johns Hopkins, recently told United Press International that the spread of CWD to Wisconsin has him looking more closely at the deaths of young people and a disease that in the past has struck only those much older.
"CWD is all the way into Wisconsin," said Johnson. "It's been found in white tail deer, not just mule deer. It's crossed the Continental Divide -- I think those are really very significant changes. What does it mean to human disease? We have no idea. But with that much movement, we want to know if it's a threat."