As chronic wasting disease hovers at our doorstep, recent discoveries about how this disease spreads – and the parts of the deer it affects – should raise our collective alert level to “red.”
Chronic wasting disease (CWD) is a brain disease that affects cervids: deer, elk, and moose. It causes an affected animal’s brain to become peppered with holes, like a sponge, leading to tremors, confusion, weight loss, and – eventually – death.
Like mad cow disease, CWD is caused by abnormally shaped prions, or proteins. Unlike mad cow disease, which has killed humans who ate affected cows, thus far there is no evidence that CWD is capable of spreading to people who eat even the most risky parts of an affected deer. It has been assumed that the only potential risk existed in the consumption of a deer’s brain and spinal cord, since those parts were known to harbor the infectious prions in a deer with CWD. So there has been a lack of concern over people contracting CWD, because people generally consume only a deer’s muscle and fat.
But some scientists, including Glenn Telling of the University of Kentucky in Lexington, suspected deer muscles of harboring the disease, spelling potential concern for hunters in CWD-affected regions. CWD has been reported in 14 states and two Canadian provinces, from the Rockies to as far east as west-central New York state.
To find out if deer muscles contain CWD, Telling and his associates injected mice that were genetically altered to be susceptible to CWD with tissue from the brains and muscles of both healthy and sick deer. As expected, mice injected with healthy deer brain and muscle tissue remained healthy, and those injected with CWD-afflicted brain tissue contracted CWD. But to the surprise of many, mice injected with the muscle tissue from sick deer – the parts people are most likely to consume – eventually came down with CWD.
At present, the focus of the northeastern states is on preventing CWD from becoming a concern by halting its eastward march. Since the spread has been strongly linked to game farms, New York, Vermont, Maine, Massachusetts, and New Hampshire have all banned the importation of live deer and elk (as well as certain parts of carcasses from CWD-infested areas). New York, Vermont, and Massachusetts have also banned the supplemental feeding of deer, while Maine and New Hampshire strongly discourage it.
Feeding deer is a problem because, besides disrupting their migration, wintering, and natural feeding patterns and making them more vulnerable to starvation and predation, it makes them more vulnerable to CWD by causing many deer to come into close proximity with one another and each other’s bodily fluids. Scientists have long known that CWD is transmissible through urine, feces, and blood; but according to a troubling new study, the disease can also spread through saliva.
Edward Hoover of Colorado State University in Fort Collins tested transmissibility in deer raised from birth in Georgia, a CWD-free state. Test deer were exposed to blood, a urine-feces mix, brain tissue, or saliva of deer that were dying of CWD. All test subjects, with the exception of those exposed only to the urine-feces mix, developed CWD.
This confirms that saliva, previously unsuspected as a CWD vector, can spread CWD and may indeed be one of the most effective agents of transmission, since deer are social animals that lick and groom one another. But direct deer-to-deer contact is apparently not necessary for transmission. Healthy deer entering deer-free areas that once held sick deer can easily contract CWD, and now, say scientists, their saliva – on the grass or another surface – is the most likely culprit. Another reason to not feed the deer – though for now, scientists believe, it’s still safe to eat them.