The Wisconsin Medical Society on Thursday warned hunters that no test can tell them whether the venison from their deer is safe to eat.

The warning comes as hunters are beginning what could be one of the most historic deer seasons in Wisconsin. A special hunt in south-central Wisconsin started Thursday with the state Department of Natural Resources hoping hunters will kill enough deer to halt the spread of chronic wasting disease. This disease is a fatal wildlife brain illness caused by an infectious, malformed protein called a prion.

The information from the Wisconsin Medical Society also comes at a time when hunters are getting a number of sometimes conflicting signals from state officials about whether they should eat venison from the deer they shoot this fall.

The DNR, for example, is paying for an advertisement heard on area radio stations lately that is a song, “CWD,” sung to the tune of “Turdy Point Buck,” that includes the line, “Bagem tagem dragem, freezem testem fryem. I ain’t afraid a no twisted little prion.”

On its Web pages, the DNR advises hunters not to eat the parts of the deer where the infected proteins that cause the disease are found. And it recommends against eating any deer that appears sick. Hunters, according to the agency, should wait for test results before eating any meat. But the agency gives little guidance about making a decision whether to eat deer that test negative.

Although the medical society reported that no scientific evidence has linked CWD to human illness, it also said that more research is necessary before a definitive answer is available.

Dr. Ayaz Samadani, a past president of the society and a member of the task force that made the report, said Thursday that hunters should base their decision on eating venison on how many CWD-infected deer have been identified in their area.

“If your deer looks healthy and there is no disease in that county, then it’s safe if it is processed correctly,” Samadani said.

The question of whether to eat the venison becomes more difficult, Samadani said, if there are infected deer in the area. The problem, he said, is that a negative test for CWD does not mean the deer does not have the disease; the deformed proteins that cause the illness may not be at a detectable level or they may be present in tissue that wasn’t tested.

So, if a hunter kills a deer in the 411-square-mile eradication zone – where 40 deer have tested positive for the disease – should he eat the meat?

“Nobody has an answer to that question,” said Dr. Dennis Maki, an infectious disease expert at UW-Madison.

The only thing everybody agrees upon is that nobody should eat meat from a deer that tests positive for the disease; there simply remains too much scientific uncertainty about whether CWD can pass to humans.

“The bottom line is that there is a mixed message coming from the science,” said James Kazmierczak, an epidemiologist with the state Division of Public Health. “No one can really say there is a zero chance.”

Kazmierczak said hunters, when considering whether to eat venison from a deer that tests negative, are forced to weigh the risk and make a decision that is based at least partly on their own willingness to take a risk. And in this case, he said, weighing risk is difficult. It’s difficult, he continued, because unlike being struck by lightning or getting in an automobile accident, there are no statistics on CWD and human illness because there are no recorded cases of CWD causing disease in people.

“To quantify risk for something that has never occurred is impossible,” Kazmierczak said.

The closest comparison, according to Maki, is mad cow disease in England. There, he said, as much as half a million pounds of infected meat entered the food supply in the late 1980s. Since then, about 120 people have died of the disease. Maki’s conclusion is that the odds of someone getting a prion disease from eating venison, even if it is from the eradication zone, is very low.

“Everybody wants zero risk,” Maki said. “For a variety of reasons, I think the risk is low. But to say it is zero is wrong.”