I didn’t really want to write about this topic since it is not directly related to The Deer-Forest Study. However, it has become evident that there is a lot of misinformation being shared about chronic wasting disease (CWD) in Pennsylvania. This blog post will try to answer some basic questions about the disease and try to dispel some myths and misinformation.

I first learned about CWD when I was an undergraduate at Washington State University. Not much was known about the disease, and what little was known was scary.

If I recall correctly (it was a long time ago!), animals in Wyoming Game and Fish’s cervid research facility were getting sick and dying. Given the condition of the animals, they at first thought it was a nutritional issue.  They’d remove all animals for a period of time.  Then replace them with more animals and they would die. They tilled the soil and sprayed caustic chemicals.  Then they placed more animals in the pen and they died!

I graduated from college and pretty much forgot about this disease.  It only occurred in Colorado and Wyoming and wasn’t much of a concern anywhere else. And I wasn’t studying cervids.

Fast forward 40 years and CWD is spreading across the U.S. and is found around the world. It has no known cure.


What is chronic wasting disease (CWD)?

CWD is caused by a prion, which is a mis-shaped protein. Proteins are complex organic compounds that occur in many different forms. Meat contains a lot of protein, as do soybeans – just different kinds. The CWD prion is similar to proteins in the brain of deer and when the prion comes in contact with those, it causes the deer protein to “mis-fold” and become a prion. This chain reaction continues.  Prions cluster around neurons in the brain creating “holes”, and ultimately death of the animal.

If you want to learn more about CWD, you can visit the PGC’s website. They have a lot of information about the disease in general as well as where it occurs in Pennsylvania.


Myths and Misinformation

There has been a rash of myths and misinformation recently in the news media and online.  While there are still many unknowns regarding CWD, there are also knowns. 


Baiting does not cause the spread of disease in deer.

This zinger is being spread by a well-known deer hunter from the Midwest. Unfortunately, nothing could be further from the truth. Michigan is a perfect example of why this statement is false.  When baiting was outlawed the incidence of tuberculosis in deer dropped dramatically. 

CWD can be spread by deer-to-deer contact and can be picked up in the environment. Feeding deer (either with food or minerals) greatly increases animal-to-animal contact. Researchers demonstrated that CWD prions were found at mineral licks in soil and puddles.

You don’t need to be an epidemiologist to know that if you walked around a shopping mall letting everyone lick a lollipop it would spread the flu faster. 


CWD is not caused by a prion but rather a certain type of bacteria.

Dr. Frank Bastian of Louisiana State University contends that CWD and other similar diseases are not caused by a prion but a type of bacterium. Unfortunately, his results have not been replicated and his hypothesis is not widely shared by CWD researchers. There is a lot we don’t know about CWD, and so this hypothesis should be pursued. But, in the meantime, there still is no cure for CWD.


Red Herring: spread of CWD does not depend on deer density.

Disease transmission may be density-dependent (more deer means faster spread of the disease) or frequency-dependent (doesn’t matter the deer density, it just spreads at a certain rate). Since we don’t really know whether CWD spreads either way, some have argued that trying to reduce deer density to reduce the spread of the disease is misguided.

This is a perfect example of trying to confuse the public and misdirect the conversation. There are more important reasons why deer density could increase the spread of CWD regardless of how disease transmission occurs.

Why density matters:

First, 1-year-old female dispersal rates increase with increasing deer density. Although female dispersal rates are lower than males (average 12%), as many as 1 in 3 females may disperse in some WMUs in Pennsylvania!

Additionally, females disperse farther than males. In Pennsylvania, female dispersal averages 11 miles, and we documented one female traveling over 150 miles before establishing a permanent adult home range. Males average about 5 miles.

Second, with lower deer densities you will have fewer 1-year-old male or female deer to disperse. This will further slow the spread of CWD.


Can prescribed fire reduce CWD in the environment?

The prion requires temperatures in excess of 2,000 degrees Fahrenheit before it is destroyed. Prescribed fire rarely reaches those temperatures, nor can it be achieved over large areas of private land.


What can be done?

The best information we have to date is that as proportion of CWD-infected deer increases, it will slowly reduce the survival of adult female deer.  Avid blog readers know that the survival of this segment of the population is most important for maintaining deer populations.

So how do we slow the spread of disease? The best tool we have at this time is to reduce deer densities because it accomplishes several things at once:

  1. It reduces dispersal of 1-year-old deer because fewer females disperse with lower deer densities.
  2. It reduces overall number of dispersing male and female deer because there are fewer of them.
  3. It will reduce the average time that infected deer spend on the landscape shedding prions and infecting other deer and the environment. Remember, some deer can be infected for 18 months before they appear sick.

Has this worked?

A few states have had success with this approach. Illinois has used targeted removals to supplement deer hunting and maintain deer densities and low prevalence. Unfortunately, because their landscape has so little forest their male deer disperse, on average, 14 miles. This makes it difficult to contain the disease, but they appear to have had some success. Colorado has demonstrated success in reducing CWD prevalence by reducing deer density using hunting and targeted removals. In the area where this was tested, CWD prevalence declined. In surrounding areas, where deer density was not reduced, CWD continued to increase. 

What’s the alternative?

Don’t like the idea of reducing deer densities?  Think there will be a cure for CWD in the near future? Ok, but the stakes are high if you’re wrong.  Here’s what happens – CWD spreads faster across the landscape, more deer in more places are infected, and the potential to cause a decline in deer populations is a reality instead of a hypothetical.

If I’m wrong and a cure is found after deer densities have been reduced, deer populations can be allowed to rebound in just a few years by reducing harvest rates on antlerless deer. Species like the white-tailed deer have tremendous reproductive potential.  A downward trend is temporary. But CWD is forever.

Given what I know, I’d say we aren’t slowing the spread of CWD across Pennsylvania. So guess who’s winning the battle to decide how to manage CWD?

-Duane Diefenbach

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