Disease Self-Defense

Texas takes steps to protect its deer and elk population from chronic wasting disease as it becomes more prolific across the United States.

By Kristen Tribe

Texas landowners and hunting enthusiasts have watched from afar as chronic wasting disease has swept across state lines infecting animals in eight states.

As the mysterious condition has spread, the Texas Animal Health Commission, Texas Parks and Wildlife Department and Texas Deer Association have joined together in recent months to discuss a surveillance program to assess the condition of Texas cervids. TAHC is also drafting updated entry requirements to better protect the state’s elk and deer populations.

"CWD has never been identified in Texas, but we haven’t looked for it," says Dr. Linda Logan, Texas state veterinarian and TAHC’s executive director.

As a first step, the importation of live white-tailed deer, black-tailed deer, mule deer and elk into Texas was suspended indefinitely in the spring.

"Texas has no intention of keeping the borders closed permanently," Logan says. "It was done to give us lead time to update rules because otherwise, potentially infected elk would have continued to be imported."

Texas Parks and Wildlife Department regulates the importation of white-tailed deer, black-tailed deer and mule deer under the provisions of the Scientific Breeder Permit regulations, while TAHC sets standards for health requirements and also issues entry permits for elk and other deer considered to be exotic to Texas.

From September 2001 through February 2002, TAHC permitted 72 elk to enter the state from Colorado, Illinois, Missouri, Montana and Oklahoma. The TPWD reports that more than 2,100 deer were imported by scientific breeders since 1998, most coming from Louisiana, Iowa, Missouri, Oklahoma and Illinois.

"As far as the quarantine – almost every other state followed suit," says Logan. "Everyone’s changing their rules. We’re not the outlier; we’re the leader."

Background of the disease

CWD was first found in a wildlife research facility in northern Colorado in the 1960s, but it was not properly identified until 1978. It is a transmissible spongiform encephalopathy of deer and elk found only in North America.

So far it has been found in wild deer in Colorado, Wyoming, South Dakota, Nebraska and Wisconsin. In captive animals, it’s been found in Colorado, Nebraska, Montana, South Dakota, Oklahoma and Kansas.

While the disease is similar to bovine spongiform encephalopathy, it is not the same thing. BSE is thought to be transmitted by ingesting infected tissues, but CWD is believed to be transmitted horizontally.

"If one elk is infected in a pen, all elk will get it …We don’t know how it goes from animal to animal," Logan says. She says that there is no evidence that sheep or cattle can contract it in a natural environment. And there is no evidence at this time to suggest humans can contract CWD, either.

The most widely accepted theory is that CWD is caused by abnormal proteins called prions. They are resistant to degradation, and they have the ability to change other proteins to become more like them.

Dr. Kenneth Waldrup, TAHC epidemiologist, says once a prion gets into a cell, it doesn’t break down, and it recruits more of them. Eventually the cell is full of prions that it can’t break down and it dies. When it dies, it releases those prions and the cells around it take them up. Then the same cycle takes happens again. As more and more cells die in the same spot, it leaves holes, which are visible in the brain of animals that have died from CWD.

Unfortunately, diagnosis is still difficult because there is no live animal test available. The only definitive diagnosis is through post-mortem examination of the brain; although, Waldrup says the Colorado Division of Wildlife is using a technique in mule deer that is closer to a live test than anything else so far.

Live deer are captured and have to be chemically immobilized so researchers can take a tonsil biopsy. Waldrup says they know in mule deer that there is a prion associated with CWD that accumulates in lymph nodes before it goes to the brain.

"By taking the tonsil biopsies, they are testing to see if it has the bad prions. If they find a positive, they’re assuming that yes, this (deer) has it, and if it’s not clinical, it will be at some point and time," he says. Waldrup goes on to explain that the difficulty with a test like this is you have nothing compare it to.

If the test is positive, it’s usually safe to assume it’s true, but if it’s negative, it leaves researchers to wonder if it really was negative or the result of a bad biopsy. Waldrup said the tests have only been conducted for about a year in Colorado and its commercial application may not be very good.

Jerry Cooke, with TPWD, says until a live test is developed, one alternative is to have a closed pen and have every animal examined for signs of CWD. If there are no signs for three to five years, it probably means it is not in your herd, as long as the deer were in a fenced area.

Regulations coming soon

Waldrup says Wisconsin was doing routine sampling in hunter-kill deer in the fall and in one area of the state they actually found several positives. Upon further sampling, they determined about 1 percent of the deer in this particular area were positive.

A survey of sportsmen in Wisconsin said a significant number do not plan to hunt deer this year. Parks and Wildlife did some figuring, and if the same thing were to happen in Texas, they would lose about 150,000 licenses.

As CWD has become more prolific, it has become more urgent for Texas to reconsider its import regulations and to address the health of its own deer population.

"In Texas … if we don’t have it, we don’t want it; but if we do have it, we want to find it," Waldrup says. "We’re in the process right now of doing a risk assessment to determine where we are going to start looking in the wild population and we’re just going county by county."

Katherine Idsal, TPWD committee chairman, says all testing at this point is voluntary, but that it is in the landowner’s best interest to be able to say the state is CWD-free, so everyone is being encouraged to participate.

Waldrup says the only way to begin their quest is to establish herd histories, by testing every that dies.

Waldrup gives a lot of credit to "the white-tail guys. Some are independent, some are with the Texas Deer Association and some are with the Texas Wildlife Association," he says. "They’re leading the charge. They’re the tip of the spear and they have stepped up and have said, okay, we’ll participate in this program."

Idsal says hunters and producers can send deer heads to the Texas Veterinary Medical Diagnostic Laboratory, and they hope to also set up deer kills for testing. She says they will first focus on the areas considered to have the greatest risk – those where elk and whitetail deer have been imported within the last five years.

At the same time TAHC hopes to have their new regulations in place by the end of the summer or early fall.

"The federal government is getting ready to pass stringent CWD rules," says Logan. "We want to make producers and ranchers prepared. We want to be ahead of the game and make sure our rules are in line with their’s."

She said people don’t realize how fast this is coming down the tracks.

Waldrup says establishing federal regulations will be difficult because almost every state is going to be different.

For example, here in Texas the regulations are confined to the four species of deer known to be susceptible, but some other states include all deer in their regulations. Plus, different agencies manage deer in every state. He says he thinks it will be difficult to come up with anything on the federal level until a live animal test is developed.

Meanwhile, back home in Texas, TPWD and TAHC are "walking a tightrope to come up with regulations that address the problem and that reassure folks but at the same time don’t cause panic. You don’t want to sweep it under the rug, but you don’t want to cause panic either," Waldrup says.

Editor's Note: Please note that after this article was
written in June, a mule deer from the White Sands Missile Range in new
Mexico tested positive for chronic wasting disease. This was the first
positive test for CWD in this state