Once deer, elk and moose are infected with chronic wasting disease, things get unpleasant quickly. The animals become emaciated and weak and start to stagger before succumbing to the disease. Chronic wasting disease has been a major concern since it was first discovered in Colorado in 1967 and scientists haven’t been able to pin down exactly how it is spread – until now. 

Researchers with the University of California - San Francisco have learned that chronic wasting disease, which is related to mad cow disease, is spread in the feces of infected animals long before they show signs of illness. The infectious agent, a form of protein called a prion, is retained in the soil where it can then be transmitted to other animals along with the plants that they eat.

The rates of transmission are highest among deer. Dr. Stanley B. Prusiner, director of the Institute for Neurodegenerative Diseases at the University of California, San Francisco and the study’s lead author, says that deer can give off the infectious agent from lymph tissue in their intestinal linings up to a year before they develop chronic wasting disease.

The prions bind to clay in soil, allowing them to persist for long periods of time. When deer graze on dirt infected with these prions, the infectious agents remain in their intestinal regions and are spread back into the soil through fecal matter. Wild herds can easily spread the disease across state lines, and in captive herds, it’s all but impossible to control.

Unfortunately, nothing can inactivate prions bound to soil outside of a laboratory environment, so the researchers say there is no chance that chronic wasting disease will be eradicated. Scientists at Colorado State University, which just received a $2.5 million National Science Foundation grant to conduct the research, will further study transmission of the disease.