My first encounter with Chronic Wasting Disease (CWD) was on a vet school projector. Shown grainy photos of skeletal elk and deer, we were taught CWD was making its way across the country in an easterly direction. Coming from across the Rockies, this disease was infecting both wild and captive cervids (members of the deer family) and moving toward Indiana (I went to Purdue University), with increasing reports in Michigan over the past year.
Fast forward to 2013 and CWD has gone beyond Michigan. With cases reported in New York, Pennsylvania, and West Virginia, this debilitating disease is here in the U.S. to stay. Hunters, ranchers, park rangers, field biologists, and veterinarians are taught to identify affected animals. So, what exactly is CWD? Is it a threat to our domesticated livestock? Is there a cure? Read on to find out more.
CWD was first identified in captive mule deer in Colorado in 1967. This disease is progressively degenerative and affects the neurological system, leading to weakness, paralysis, and death, primarily from starvation — a wasting disease in every sense of the word.
Similar to some other neurodegenerative wasting diseases like mad cow disease, CWD is classified as a spongiform encephalopathy. Whereas diseases such as mad cow disease have been confirmed to be caused by a novel infectious agent called a prion, which is essentially a protein folded in an incorrect way, resulting in tissue damage, the presence of prions in CWD cases has yet to be confirmed; currently, prions are simply presumed to be the cause. Where CWD originated is not known.
CWD appears to be easily transmissible between wild and captive deer and elk, but the exact mode or modes of transmission are not understood. There have been no documented cases of CWD in domesticated livestock such as cattle and small ruminants. There has also not been any evidence to show that humans are susceptible. However, hunters in CWD known areas are advised to not eat animals that look sick or were tested positive for CWD (hunters can send samples of nervous tissue to certain labs for diagnosis on any kill). Additionally, hunters that field dress are advised to wear gloves and minimize handling of the brain and spinal cord.
As with the other spongiform encephalopathies, there is no treatment for CWD and no vaccine. Both federal and state governments have instituted surveillance programs to gather data on this spreading disease. Brain samples from road kill and a percentage of hunted animals are periodically sent to diagnostic labs for testing to find out more about disease prevalence. For farms that raise captive cervids, many states have mandatory monitoring programs.
Large animal veterinarians in states such as Colorado and Wyoming, where CWD is much more prevalent and there are larger numbers of farms raising captive deer, are exposed to this disease much more frequently than my measly slide presentation prior to graduation. I do not have any captive deer patients and my exposure to the wild deer population is limited mostly to the animals I see in the fields and woods from a distance. However, it’s important to know what the wild animals are harboring in our own backyards.
Dr. Anna O'Brien