The mystery of how deer and elk spread chronic wasting disease from one animal to another may be solved: Their tongues are infectious.

When the animals lick or slobber on each other - a fairly common occurrence - the agent that causes the fatal disease may be shed from their tongues via saliva. And when they graze, leaving sloughed-off tongue cells and saliva in grass and soil, the disease could be widely transmitted.

Richard Bessen, an associate professor of veterinary molecular biology at Montana State University in Bozeman, discovered the infectious agent, called a prion, in deer and elk tongues. Details of disease transmission still need to be worked out, he said, but he believes the prions in saliva are significant in the growing national epidemic of the disease.

But a Wyoming Game and Fish Department official said the discovery hasn't really proven anything regarding transmission of the disease.

Terry Kreeger, supervisor of Game and Fish Veterinary Research Services, said in an e-mail from a hunting trip in Minnesota this week that the new research shows that the chronic wasting disease prion is in the tongue, and "that is all."

Game and Fish Department officials said the agency has been conducting research for several years on the disease and is continuing with a massive surveillance program that aims to track the spread of the disease. Officials said the department's research continues to focus on various possible means of transmission in deer and elk, including through saliva, feces and urine.

Chronic wasting was first detected in the Rocky Mountain region in 1967. The disease has been endemic in a 12,000-square-mile area of southeast Wyoming and northwestern Colorado for more than 30 years. The disease has now spread to a dozen states and two Canadian provinces.

Last month officials in West Virginia and Alberta announced their first cases of the malady in wild deer, an indication that the problem is still spreading. And last week the Colorado Department of Wildlife said it had found it in a wild bull moose for the first time.

Chronic wasting disease belongs to a group of fatal maladies called transmissible spongiform encephalopathies, which include mad cow disease and sheep scrapie.

Infectious prions are also found in sheep tongues, Bessen said. He presented his findings at the Second International Chronic Wasting Disease Symposium held in Madison, Wis., in July. Results should be published in the next few months.

The findings "are pretty convincing," said Dr. Patrick Bosque, a neurologist and expert on prion diseases at the Denver Health Medical Center, who added, "Up to now, no one has been able to show how the disease spread from deer to deer."

The U.S. Department of Agriculture, which provided the tissue samples used by Bessen, declined to comment until the findings are accepted for publication in a scientific journal.

The details of how prions get into certain animals have been worked out, Bessen said. When cows, sheep, monkeys or other animals eat feed contaminated with prions, the infectious particles land in their guts. From there they invade lymph tissue and nerves that travel from the gut into the spinal cord and the brain.

But wild deer and elk are not likely to eat contaminated feed. Somehow the disease is spread from animal to animal, via the environment.

The question is how prions move from the brain to peripheral tissues and how are they shed.

"We decided to focus on the tongue," Bessen said. It is a muscle with extensive nerve connections to the brain and the central nervous system. Some nerves make direct connections with taste cells, which shed into saliva. And a type of tonsil tissue found at the back of the tongue is a potential target for prions.

"Prions love nerves," Bessen said. "They jump on them and go."

Experiments clearly show that the tongues of elk and deer contain prions, Bessen said. Nasal tissue is also infected. Other experiments with hamsters show that prions travel specifically to taste buds on the tongue, raising the possibility that the same happens in deer and elk.

So far there is no evidence that people exposed to chronic wasting disease are in danger of contracting it or any related prion disease.