This beautiful young white-tailed deer is healthy and alert. He shows no signs of the deadly Chronic Wasting Disease that is occurring in some deer, elk, and moose populations. Robert Benson Photo.
07/10/2015 – Mad Deer Disease Is Bad News
When my husband said that “Mad Deer Disease” had been detected in south Texas, I thought he was joking. I said “There is no such thing as mad deer disease.” Or is there?
I had never heard of mad deer disease before this conversation. But it does apparently exist and has been known for almost 50 years. It is more accurately called Chronic Wasting Disease. CWD, as it is referred to, is a fatal disease affecting the brains of white-tailed deer, mule deer, elk and moose.
And this is bad news.
Chronic Wasting Disease was first identified in captive mule deer in a Colorado research facility in 1967. Since that time, the disease has been detected in 23 states and two Canadian provinces. It was first reported in Texas (in the Hueco Mountains of far west Texas) in free-ranging mule deer in 2012. And just last week Texas Parks and Wildlife Department confirmed the disease in a white-tailed deer that died in a breeding facility in Medina County, Texas.
As I said, this is bad news.
CWD was determined in 1978 to be a type of Transmissible Spongiform Encephalitis (TSE). Mad cow disease is also a TSE and is technically called bovine spongiform encephalitis. A similar disease, called scrapie, affects sheep. All these diseases cause a slow wasting away of the animal’s body. After losing weight and condition, the affected animal shows behavioral symptoms such as aggression, lowering the head, and walking in set patterns. The erratic behavior of cattle infected with the TSE earned it the name “mad cow disease.”
You may recall that mad cow disease burst into the news in 1986. A downer cow in Great Britain was found to have the neuro-degenerative disease when it was sent to the slaughterhouse. It was unable to stand. Upon post-mortem examination, its brain and spinal cord had spongy lesions. Other cows were discovered with the same symptoms and brain lesions. Investigation showed that many cows in the United Kingdom at that time were being fed a protein supplement made from the discarded meat of other domesticated animals (including downer cows). The infectious agent was apparently a protein substance transmitted via this feed. The practice was promptly stopped.
Unfortunately, a similar disease called “variant Creutzfeldt-Jakob disease” began being diagnosed in people. It is almost certainly linked to consumption of beef, particularly beef contaminated with the brains, spinal cords, and certain other tissues from TSE-infected cows. Over 400,000 infected cows had entered the human food chain before the problem was detected. As a result, as of June 2014, in Great Britain alone, 177 people have died from this form of Creutzfeldt-Jakob disease. Fifty-two people elsewhere have also died. It is a disease that progresses very slowly, taking 2.5 to 8 years to develop in cattle, and maybe decades in humans. Even though thirty years have passed since the outbreak occurred, more cases may still turn up.
TSE diseases are not new. They have been around for centuries. Hippocrates (in the 5th century BC) reported such illnesses in cattle and sheep. Quite possibly these neuro-degenerative diseases have been with us for a long time.
What is new is the increased numbers of cases. This is partly due to increased numbers of animals in smaller areas. And we humans may be helping these changes along. Certainly, feeding infected protein to cattle created the serious problems in the beef industry.
But what is going on with the disease in deer? To date, fortunately, CWD does not seem to be transmissible to species other than deer, elk, and moose. But how are they getting it?
Biologists believe that CWD is endemic in the grasslands of Colorado and Wyoming. Perhaps it even originated there as a genetic mutation. The disease produces a misfolded protein. The resulting particle, smaller than a bacterium, is called a prion. Somehow these prions act as templates for more prions to develop. These prions collect in the nervous system of the infected animal. Eventually the diseased animal dies. If some other animal feeds on the carrion, it takes in the prions. However, no other species have been found to be susceptible to the CWD prions; just deer and elk. But deer and elk are herbivores; they do not scavenge on dead animals. How are they contracting CWD?
Recent discoveries are indicating something surprising. The prions are being found in all of the diseased animal’s tissues (not just nervous tissue). Worse still, researchers have discovered that prions are excreted by the sick animals in their feces and urine. And prions are nearly indestructible. Ultraviolet light, chlorine bleach, and high heat (up to 1,100 degrees F) won’t denature the prions. Even worse, they collect in the soil and bind to plants’ leaves and roots.
This is really bad news. Areas where sick deer have been are littered with these microscopic infective prions. Any healthy deer ingesting plants in these areas are also ingesting prions. And more cases of CWD are showing up.
Is there any risk to humans or domestic animals? Scientists say no. Even the World Health Organization has weighed in, citing examination of all the studies available, and has concluded that “currently there is no evidence that CWD can be transmitted to humans.”
Nonetheless, officials are advising caution. Hunters and naturalists in the field should be alert for unusually thin deer, and deer acting abnormally, or walking with difficulty. Report such incidents to state wildlife agencies.
Only two cases of CWD have been reported in Texas. Two cases do not an epidemic make. But we should be vigilant in observing all of TPWD’s regulations regarding the hunting and handling of deer. After all, with appropriate regulations, the world’s beef industry has survived mad cow disease. Now, it’s time to protect wildlife and the hunting industry.
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