Chronic wasting disease might be passed in the blood and saliva of infected deer, according to a Colorado State University-led study published in the Oct. 6 edition of Science.

Researchers say the findings raise new questions about whether the disease can be spread by blood-sucking insects or social contact between animals. Moreover, the evidence suggests that no tissue from an infected animal can be considered free of disease-causing prions.

Chronic wasting disease is a degenerative brain disease in cervids characterized by weight loss leading to death. It was discovered in 1967 in mule deer at a wildlife research facility in Colorado. Today, CWD has been found in free-ranging and captive deer and elk in 14 states and two Canadian provinces.

The research team tested the blood, saliva, feces, and urine of CWD-infected deer to determine how the disease is passed between animals. Infectious prions were discovered in the animals' tonsils as soon as three months after exposure to saliva or blood from an infected deer.

Scientists have been at a loss as to how animals were infecting one another with the fatal disease agent. "This study shows for the first time that CWD can be passed to deer that come into contact with the blood and saliva of infected deer," said study leader, Dr. Edward A. Hoover, a CSU Distinguished Professor in the Department of Microbiology.

Grooming, licking, and nuzzling are important social interactions among deer and elk—behaviors that are accompanied by salivary exchange.

Although there are no known cases of CWD transmission to humans, people should avoid bodily fluids from CWD and other prion infections, Dr. Hoover said. "The study also causes us to reconsider a potential role for blood-feeding insects such as mosquitoes and ticks in the transmission of CWD or other prion infections," he added.

The study was conducted during an 18-month period with financial support from the National Institutes of Health.