Chronic Wasting Disease (CWD) was found in 2 free-ranging wild deer in Macon County Missouri last Fall. Three more have been found since.
This bad news may indicate a dark future for our deer herd, but understanding this situation – and assessing how, when and how badly we may be impacted is not easy.
CWD will be a huge topic in Missouri for the next few years, possibly for the rest of our lives. The more clearly we understand the disease, the more productive public discussion will be. I hope you stick with me a bit while I provide some background on this complex topic.
Let’s start with a glossary of a few basic terms:
|TSE||Transmissible Spongiform Encephalopathy , a group of incurable fatal diseases. Some are contagious. Almost always species-specific. TSE's are very different from generally understood diseases (viral, bacterial, fungal, parasitic).|
|Prion||A malformed or "misfolded" protein with the ability to cause healthy proteins to similarly malform. They are the agent responsible for TSEs. Their method of infection sidesteps immune functions.|
|BSE (Mad Cow)||Bovine Spongiform Encephalopathy. Also known as Mad Cow disease. A TSE that affects cattle. Unique among TSEs in that it jumped from its host species to humans. Not contagious through contact or soil, but is transferred through the consumption of bone, brain and nervous tissues from an infected animal. Some of these tissues were commonly included in commercial livestock feed before the disease was understood. Changes in the animal feed industry and meat processing practices have nearly elimintated BSE.|
|CJD||Creutzfeld-Jacob Disease [ˈkroits-felt ˈyah-kawp] , the human TSE. Afflicts about 1 of every million humans worldwide. Average age for symptoms to appear is 68. The USA has about 200 CJD fatalities annually. Not contagious.|
|vCJD||Variant Creutzfeld-Jacob Disease. This is the label scientists assign to BSE when it jumps species to infect a human. A couple of hundred people worldwide have died of vCJD since an outbreak that was mostly concentrated in Britain, where it killed 28 humans at its peak in 2000. The average age for symptoms to appear is 26. Consumption of BSE infected beef products - likely those contaminated by nervous system tissue - is thought to be the cause. Only 4 cases of vCJD have ever been found in the US, each believed to have been contracted overseas. vCJD has been nearly eliminated as a result of progress against BSE, and new processing practices which exclude nervous tissues from meat products.|
|Scrapie||A contagious TSE of domestic sheep and goats. First documented in England nearly 300 years ago but only recently identified as a TSE.|
|Cervid||An animal from the taxonomic family "cervidae". Whitetail, Mule deer, Elk, Moose and Caribou are cervids native to North America. Some non-native cervids commercially raised in North America are Reindeer, Red Deer (often crossbred with elk), Sika Deer, Axis Deer and Fallow Deer.|
Chronic Wasting Disease. A contagious TSE affecting cervids. Transmissible primarily via animal to animal contact. Also via soil contaminated by the saliva, urine, feces and eventually the carcasses of infected cervids. Contaminated soil remains infectious for many years, the exact duration not yet known. Though TSE's specific to a few domesticated or confined species have been documented, CWD is the only contagious TSE known to spread among wild free ranging animals anywhere in the world. There are several dozen cervid species around the world, but CWD has so far only been detected in the US, Canada, an isolated infection in South Korean resulting from the importation of infected breeding stock from North American game farms, and in 2016 found in Norway in wild Reindeer and Moose.
|Captive Cervid Industry||An industry involving the trade in and confinement of privately owned cervids such as deer and elk behind escape resistant fencing for breeding, shooting and other purposes.|
A word often appearing in research, describing a disease which can transmit from animals to humans.
TSE’s are very different from the types of diseases we are familiar with, such as those caused by virus, bacteria, fungus or parasite. The infectious agent is the prion, something first identified only 30 years ago. They are the subject of intensive current research..
CWD is contagious, transmitted though social contact (nose to nose, social grooming, etc) as well as environmentally through saliva, urine and feces, and eventually through the carcasses of affected deer. The incubation period is at least 16 months, and external symptoms do not normally appear until late in the infection. CWD tests require dead deer. There is currently no live test.
Once in an environment, CWD prions remain viably infectious for a very long time – perhaps as much as 20 years. There is no known practical method of clearing an infected area. Healthy deer introduced to supposedly cleaned and disinfected pens have developed CWD. Prions are not "alive" and thus cannot be "killed". They are extremely resistant to being rendered inert, apparently unaffected by chemicals and temperatures normally used in sterilization or decontamination.
CWD was first diagnosed in a captive deer at a Colorado wildlife research facility in 1967. In 1981 it was found in a wild Colorado Elk. Soon after it was found in Wyoming. It continues to expand to neighboring states, but has also “hopped” to geographically distant areas – such as Missouri. It is now in 17 states and two Canadian provinces.
Though it is impossible to absolutely prove that the captive cervid industry is responsible for the spread of CWD, there is abundant evidence. Despite 10 years of statewide testing, thus far all infected wild Missouri deer have been found within 2 miles of a North Central Missouri captive cervid facility in which infected animals had already been detected. This is consistent with CWD discoveries in most other states.
The sale and transportation of infected animals to game farms in areas harboring CWD could be responsible for the spread of the disease to distant areas.
Hunters unknowingly transporting infected carcasses back home after a successful western hunt are another possible source. For instance, there are no confined cervid facilities anywhere near where the disease was found in West Virginia. There is just no way to definitively prove what is the real cause.
I’ve read and heard some hunters claim that CWD is just part of nature, that it must have been around for a long time and nature will find a balance.
I spoke about that with MDC Whitetail Biologist (and CWD point man) Jason Sumners. He responded “That’s simply untrue. I would say in the last 4 to 5 years we’ve finally begun to gain enough knowledge on some of the situations going on in Colorado and Wyoming to have a better understanding of what is happening.”
Sumners explained that CWD is unlike any other disease, saying “It is very clear that CWD becomes a very slow drain on the population. When many people talk about deer diseases, they want to correlate everything with EHD or Bluetongue, and the disease doesn’t function that way. It maintains itself in the system. It doesn’t disappear like viruses that crop up and go away. As it accumulates and increases in frequency, mortality begins to exceed birth rates, and populations decline. They’ve seen a 50% decline in areas out west in the last decade.”
And it is not slowing down. Percentage of infected animals continues to rise, and populations continues to fall. It kills every animal it infects. The potential future is quite grim.
But attempts to manage outbreaks have shown some measure of effecitveness. While Wisconsin, Colorado and Wyoming have significantly impacted deer herds, outbreaks in Illinois and New York have been thus far held to much more limited scope. There is hope that Missouri's effort, which has much in common with Illinois and New York, may be similarly effective at controlling the outbreak and at least slowing the spread of the disease.
In order to better gauge the prevalence and distribution of the disease, in February the MDC set about killing 600-700 deer in the area surrounding the positive samples.
Three tested positive. The MDC will take what they learned in those tests and decide on future management actions.
Hunters and their families of course are concerned about the safety of the venison in their freezer. And honestly, there is no expert that will tell you the risk is zero.
They will say that despite decades of people hunting deer and elk in the high-CWD areas of Colorado and Wyoming, no human related TSE has been confirmed. Ever. Anywhere. It appears that, unlike “Mad Cow disease” which jumped from cattle to humans, the inter-species barrier for CWD is holding – as it does with most TSEs. But there are no guarantees for the future.
Prions concentrate in the lymp nodes, brain and spine. Despite the apparent absence of risk, field dressing and butchering techniques that avoid contacting or disturbing those areas seem prudent. And the saw that you use to remove antlers should probably be permanently kept separate from any other butchering duties. And leave the spine intact. As has always been the case, any animal showing apparent signs of illness should not be handled and certainly not consumed.
CWD is a complex topic that cannot be done justice in a single magazine article. I’ve put together a simple website with resources that will help you learn more, at http://NoMOcwd.org.
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