You may have heard of a weird disease in deer called the “Zombie” deer disease, which is really Chronic Wasting Disease ( CWD). This is a contagious always-fatal neurologic disease affecting cervids (deer, elk and moose), that is contributing to declines in herds and raising the possibility of local extinctions. It has been identified for 40 years in Western states, but recently has been popping up occasionally in Texas in mule deer on the New Mexico border and some captive fancy deer herds near San Antonio. It is not in our native white tail deer population yet.
What it is? CWD belongs to a group of diseases known as transmissible spongiform encephalopathies (TSEs). Within this family of diseases, there are several other variants that affect domestic animals: scrapie, which has been identified in domestic sheep and goats for more than 200 years, bovine spongiform encephalopathy (BSE) in cattle (also known as “mad cow disease”), and transmissible mink encephalopathy in farmed mink.Several rare human diseases are also TSEs. Creutzfeldt-Jakob disease (CJD) occurs naturally in about one out of every one million people worldwide. Variant Creutzfeldt-Jakob disease (v-CJD) has been associated with the large-scale outbreak of BSE in cattle herds in Great Britain.
What are symptoms? It causes a characteristic spongy degeneration of the brains of infected animals resulting in emaciation, abnormal behavior, loss of bodily functions and death. While yearlings and even fawns can contract CWD (often getting the disease in utero from their mother), late-stage CWD symptoms are usually only visible in adult animals because of CWD’s long incubation period (usually around 18 months but may be as long as two years). In most cases, animals with CWD show no visible, outward symptoms of the disease for all but the last few months of the disease’s cycle. Thus, the majority of infected animals are virtually impossible to distinguish from healthy, non-infected animals. Because CWD affects the neurological system of an infected animal first, other causes of mortality (predators, vehicle collisions, other diseases) usually remove the animals from the population far before outward signs of the disease become apparent.
However, if an infected animal survives to the final stage of this always-fatal disease, the most obvious and consistent clinical sign is emaciation. CWD affected animals continue to eat but amounts of feed consumed are reduced, leading to gradual loss of body condition. Excessive drinking and urination are also common in the terminal stages.
Behavioral changes also occur in the majority of cases of late-stage CWD, including decreased interactions with other animals, listlessness, lowering of the head, blank facial expression and repetitive walking in set patterns. In elk, behavioral changes may also include hyper-excitability and nervousness. Excessive salivation, drooling and grinding of the teeth also are observed. This is where it got the “zombie” nickname.
Why is it important? CWD poses serious problems for wildlife managers and the implications for free-ranging deer and elk are significant. Where it occurs, CWD alters the management of wild deer and elk populations. Ultimately, perceptions about human health risks associated with all TSE’s may erode hunter’s confidence and their willingness to hunt in areas where CWD occurs. This would be a huge hit to Texas deer hunters if people were afraid to eat venison.
Can humans get it? Scientists don’t think so, but health and wildlife officials advise caution. Hunters are encouraged not to consume meat from animals known to be infected. In addition, hunters should take common sense precautions when field dressing and processing deer or elk taken in areas where CWD is found.
How can we control/prevent it? Migrating wild animals are hard to control. States are trying to stop cervids from crossing state lines, running surveillance programs and vaccines are being developed. The latest in vaccine testing was in my vet news this week, but it wasn’t 100% effective in the test cases.
For more information:
http://cwd-info.org/faq/
https://www.cdc.gov/prions/cwd/index.html
https://www.avma.org/News/JAVMANews/Pages/170815a.aspx
https://www.avma.org/News/JAVMANews/Pages/180915l.aspx
https://www.avma.org/News/JAVMANews/Pages/190701l.aspx
