Prevalence of chronic wasting disease -- a cousin to mad cow disease that affects deer, elk and other cervids -- is on the rise in western Kansas, according to a biologist with the state's top wildlife agency.

The Kansas Department of Wildlife, Parks and Tourism recently announced that, of the 363 deer samples collected and tested since the start of the fiscal year, 37 of them tested positive from CWD.

Shane Hesting, wildlife disease coordinator for the KDWPT, told The Topeka Capital-Journal this week that most of those samples were hunter kills in southwest Kansas, because that was the zone of surveillance this past season. The state has five zones of surveillance, which are areas where the KDWPT focuses its sampling efforts during any given year, and the surveillance zone rotates clockwise on a yearly basis around the state. Deer from other zones also are tested, but typically on the hunter's dime unless the animal shows signs of having the disease.

During the past several years, Hesting said, northwest Kansas in particular has seen a noticeable increasing trend percentage-wise in the number of CWD positives.

"I guess over the last five or six years, it's an increasing trend of prevalence," Hesting said. "We used to have statewide surveillance where we'd collect 2,800 or 2,500 samples statewide from hunters and we'd end up with a half of a percent prevalence out of the total, and all of them are in the west.

"But now, it's 10 percent of the sample size is positive ... and probably over half of those positives come from the northwest, because we test sick and suspect animals on a statewide basis. So, we're seeing a lot more sick ones in the northwest, which is indicative of an increasing prevalence trend."

Part of the reason for the increasing prevalence of CWD positives is because the disease has an incubating period in which the deer appears to be otherwise healthy. During that time, it spreads the disease through excretion of bodily fluids that contain the abnormal prions that cause the disease. When deer interact with each other, they can spread the disease to other deer that come into the area.

"The abnormal prions that cause CWD, as soon as an animal gets it, it starts incubating," Hesting said. "So, we know that the prions are excreted in saliva and feces, so another deer could pick those up at any time the animal becomes infected. As the time increases for the animal that has the disease, of course they're going to be dumping more prions out onto the landscape and then transferring to other animals and so forth."

This makes methods like baiting with feeders an increasingly risky practice, because it causes deer to congregate. When deer are concentrated around a food source, the disease can easily spread to several other animals, causing a snowball effect where the disease spreads exponentially through an area's deer population.

"Another thing about sick animals is that you start seeing more and more of those the longer the animal has the disease," Hesting said. "So, the more animals you have incubating the disease and then making it to symptomatic stage increases over time. In my opinion, it takes about 10 years from when you get CWD to when you start seeing sick animals on the landscape. That's probably a close rule of thumb, it probably varies state to state.

"The more of the sick ones you have, of course, they're going to be more obvious to the public who are reporting those animals. When you have just a few sick animals out there, the predators take them out and then they're just not visible to the public, so you're just not getting those reports. So it's a function of prevalence -- how high the occurrence level is in the population, and then how long it's been out there."

Eastern Kansas

Hesting said that eastern Kansas has been free of the disease when it comes to testing, though that doesn't mean CWD is absent from the area or that it couldn't begin showing up.

"We haven't had a detection in the eastern half of Kansas that we've found," Hesting said. "Typically, when you're a state that has CWD, we say that the prevalence or the occurrence of a disease is below the detectable level when you're not finding it. It could possibly be there and probably is there but is just not showing up in your sample size."

Because the disease has such a long incubation cycle, animals can be infectious for a long time without even showing signs of having the disease.

"Symptoms are something that you'll read about or hear about a lot, but really they only show up in the last few months of the disease cycle," Hesting said. "So, three-fourths of the time that the animal has CWD they look apparently healthy, it's only in the last few months they start drooling and really became emaciated and disoriented and lethargic."

Hesting said one of the main ways to prevent the disease from spreading is to not move carcasses, especially from infected areas to uninfected ones. However, he said, the best method would be to not move live animals, either, something that the government wildlife agencies and deer and elk farmers are taking to heart as they can't easily determine whether a live animal is infected. He said fish and wildlife agencies for the most part have put a lot of animal relocations on hold for now.

"There's a live-animal test, they can look at the tonsils and they can look at the anal mucosa of the deer or the elk, but they are not sensitive enough. They miss a lot of positives," Hesting said. "So, really, the most valid test comes from an animal that's dead. You can pull the lymph nodes out of the head that way and the obex and brain stem and get probably close to 90 percent sensitivity or greater."

Future testing

During the next fiscal year, which begins July 1, the KDWPT's zone of surveillance will rotate to the 12 counties in the northwest corner of the state.

"So four over and three down, those counties," Hesting said. "We like to get the 2 1/2 years and older deer for testing, routine surveillance. A hunter can have those tested for no charge if they're in the northwest corner. If they're outside that northwest zone, then they have to cover the cost themselves. We can help them, and there's a good video on YouTube of how to pull the sample. They can type in 'K-State CWD' to bring it up and it'll show how to pull the right sample out of the animal."

Hesting said hunters or landowners can either ship the sample or take it directly to the Kansas State Veterinary Diagnostic Laboratory, 1800 Denison Ave. in Manhattan. He said the cost for the test this year was $28. Those who requested the $7.50 sampling kit also received a shipping label in the kit that allowed them to ship the sample to the lab free of charge.

While it does cost some money to test a deer or elk from outside the surveillance zone, it may be a good idea to do so just for peace of mind before eating the animal's meat, especially in an area that is known to carry the disease.

"Right now, with CWD, there hasn't been a transmission to people in the United States, but the CDC is urging caution because TSEs (transmissible spongiform encephalopathies) having an incubation time and there could be something we don't know about yet," Hesting said. "So, we don't recommend eating sick wildlife and we don't recommend eating a deer known to have CWD. So if they did a test and it came back suspect or positive, we would not recommend eating that animal."

Hoof rot

The state also has battled with a form of hoof rot disease in the past several years that peaked during the 2016-17 deer season. With the unusually wet winter the state has experienced this year, it may again become an issue this year if the heavy precipitation continues into the summer and fall.

"We have it every year, and it seems to correlate with wet weather," Hesting said. "So, wherever we've had above-normal precipitation, we have more hoof rot in those areas. That's unrelated to CWD. In Kansas, hoof rot's caused by secondary bacterial infections, which come on after the hoof has been injured either by running over rough terrain -- during the rut, especially, the bucks are more prone to hoof disease because they're running over rough terrain, getting injured, getting punctures in their hoofs and so forth -- and then those bacterial infections start the process of hoof rot.

"We had a few this year but it's nothing like, I think three years ago, we had a lot more. The trend was higher three or four years ago. We get some every year because of the rut and deer on their feet a lot moving around, but not like in the past, so far."