Recent research at Colorado State University (CSU) and published in the journal Science (vol. 314: 133-136) suggests that chronic wasting disease (CWD) can be spread from one animal to another through their saliva, reports the Wildlife Management Institute.

CWD is a neurological disease of cervids (deer) that belongs to a family of diseases known as transmissible spongiform encephalopathies, or prion diseases. The disease attacks the brains of infected deer, elk and moose, causing the animals to become emaciated, display abnormal behavior, lose bodily function and die. There is no evidence that the disease is linked to any neurological disease that affects humans. At present, the disease has been found in 14 states and 2 Canadian provinces.

The mode of CWD transmission among animals has been a matter of conjecture. Its transmission is unusual because, unlike its very hard-to-spread, pathogenic relatives, it seems to spread fairly readily from animal to animal. Other body fluids, such as blood and urine, have been suspected. In fact, blood has been known to transmit other prion diseases. However, the seemingly easy transmission of CWD prompted speculation that saliva is a key vector. Normal cervid behaviors of nuzzling or grooming, especially during breeding season, would facilitate transmission through saliva.

The recent research was done with tame, tractable white-tailed deer fawns hand-raised in Georgia, away from any known source of CWD. Use of tame fawns allowed the researchers to handle the animals safely and easily in order to expose them to saliva, blood, urine, feces, and injected or orally administered brain tissue from infected free-ranging or captive Colorado mule deer that were CWD positive. The saliva was squirted into the mouths of the test deer.

The exposed deer were housed in a specialized lab for up to 18 months. Biopsies of tonsil tissue were taken periodically during that time period, to look for presence of CWD prion. At the end of the study, brains from the study animals were autopsied. All three of the saliva-exposed deer demonstrated symptoms of CWD, as did three deer given a single transfusion of blood from a CWD-infected deer. The three deer exposed to urine and feces, and the two control deer showed no symptoms.

The researchers cautioned that these results did not rule out urine and blood sources, because of the small number of test animals.

These CWD-positive results are significant and improve understanding of how the disease spreads. It has been known for some time that, even if infected deer are removed from a pasture, newly introduced deer can become infected with the disease. In latter stages of CWD, an infected animal demonstrates excessive drooling and drinking of water. Deposits of saliva could be a significant source of disease contamination and later transmission.

A logical next step in CWD research will be to study how infectious prions contaminate the environment.

To learn more about CWD please see the CWD Alliance website at www.cwd-info.org/index.php.