Wasting Deer: Deer saliva and blood can carry prions

For the first time, researchers have shown that saliva alone can transmit a brain-destroying disease from one animal to another.

Three oral doses of saliva from a deer sick with chronic wasting disease passed the infection to other deer kept in isolation suites indoors, reports Edward Hoover of Colorado State University in Fort Collins. The finding gives substance to worries that the disease spreads through such deer social habits as touching noses and licking to groom each other.

The study also found that both an injection of blood from a sick animal and exposure to infected brain tissue transmitted the infection, Hoover and 16 colleagues report in the Oct. 6 Science.

Fourteen states and two Canadian provinces have reported chronic wasting disease, which strikes mule deer, white-tailed deer, Rocky Mountain elk, and occasionally moose. The disease belongs to the cluster of deadly brain ailments, such as mad cow disease, that are spread by misshapen prion proteins (SN: 11/30/02, p. 346: Mad Deer Disease?). No case of human disease has been traced to game, but researchers haven’t ruled out the possibility.

Biologists have known that animals can catch the disease simply by occupying an area where sick animals once lived. Contaminated land has vexed researchers, who don’t want to risk introducing chronic wasting disease into diseasefree regions but don’t want tests confounded by dirty fields.

For the new study, researchers at the University of Georgia in Athens supplied 14 white-tailed deer fawns. The state is free of chronic wasting disease. Researchers in Colorado kept the animals indoors during their 18-to-22-month lives and dosed them with material from sick mule deer.

Although saliva, blood, and brain tissue transmitted the disease, three oral doses of mixed urine and feces didn’t have an effect. However, Hoover cautions that the two animals that received that material carried gene variants known to render deer less susceptible to prion infections.

Four cases of the human version of mad cow disease have been traced to blood transfusions, but Hoover notes that no study of another prion disease has shown transmission through saliva.

The saliva result is “the exciting part of this study” for wildlife managers, comments wildlife-disease specialist Margo Pybus of Alberta’s Fish and Wildlife Division in Edmonton. The dose in the study, 50 milliliters of contaminated saliva, is large enough to be “unlikely” in the real world, she says, but further research may define how small a dose of saliva can transmit the disease.

The new study “lends tremendous credibility to regulations that restrict baiting and feeding of deer,” says Bryan J. Richards, who leads the chronic wasting disease work at the National Wildlife Health Center in Madison, Wis. To fight the disease, states are now banning hunters’ once-common practice of setting out deer feed. In theory, deer clustering around the windfall might increase unsafe social contacts. “A lot of states have been ridiculed because there was no proof” of danger from deer baiting, says Richards.