No vaccine, always fatal; what to know about chronic wasting disease and risks to humans;
| Food Safety News – Just as hunters have been stalking deer and elk, so, too, has a deadly brain disease been stalking their four-legged quarry.
Known as a chronic wasting disease (CWD), it infects deer, elk, and moose. It was first confirmed in Colorado in the 1970s.
Back then, wildlife officials thought it would take more than 100 years to find its way east. They were confident that the Mississippi River would serve as a natural border.
But since being confirmed in Wisconsin in 2002, it has made its way to 25 states, most recently into Mississippi and Tennessee, and two Canadian provinces.
News headlines warn that it’s now within miles of the Alabama state line, approaching Indiana, and looking like it might get into Idaho.
“It continues to spread,” said Kip Adams, the conservation director for the Quality Deer Management Association.
The affected states are Colorado, Illinois, Iowa, Kansas, Maryland, Michigan, Minnesota, Missouri, Montana, Nebraska, New Mexico, Mississippi, New York, North Dakota, Ohio, Oklahoma, Pennsylvania, South Dakota, Tennessee, Texas, Utah, Virginia, West Virginia, Wisconsin, and Wyoming. The two Canadian provinces are Alberta and Saskatchewan.
Lou Cornicelli, Minnesota’s Department of Natural Resource wildlife research manager, said that managing CWD is challenging because of how it spreads and persists in the deer population. For example, males are much more likely to have CWD than females; male deer also move the disease farther on the landscape because they typically travel longer distances, especially in the fall, when hunting season is on.
According to the U.S. Centers for Disease Control and Prevention, it is possible that CWD may also occur in other states without strong animal surveillance systems, but that no cases have been detected yet.
Also according to CDC, once it is established in an area, the risk can remain for a long time in the environment. The affected areas are likely to continue to expand.
What about humans?
For humans, this is a concern that goes past the deer. That’s because CWD, along with mad cow disease (bovine spongiform encephalopathy, or BSE), scrapie in sheep, and Creutzfeldt-Jakob in humans, is among a family of brain diseases known as transmissible spongiform encephalopathies (TSEs).
In these diseases, holes develop in the brain, causing the brain to become spongy. (Story continues below … )
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Symptoms of Creutzfeldt-Jakob in humans include psychiatric and behavioral changes, trouble walking, loss of weight, and problems with memory and thinking.
There is no vaccine for it, and it is always fatal.
Symptoms in deer are similar: the animal becomes emaciated and exhibits abnormal behavior. As in humans, it is always fatal.
Although humans can become infected with mad-cow disease (bovine spongiform encephalopathy) from eating beef products contaminated with central nervous system tissue, such as spinal cord and brain, from cows infected with the disease, there is no record of anyone coming down with the human variant of chronic wasting disease from eating infected deer, elk or moose meat.
In addition, current thinking is that mad cow disease and chronic wasting disease are “distinctly different.”
Even so, Claudio Soto, professor of neurology at the University of Texas, told Food Safety News.com in an earlier interview, that even though there have been no confirmed cases of infections in humans from CWD, the public should know that “it’s a possibility that needs to be explored.”
“I don’t want to scare people,” he said, “but these CWD prions are accumulating, and prions have a long incubation period — sometimes as much as 30 to 40 years in humans.”
Much smaller than bacteria, prions are single proteins that can’t be destroyed by typical “kill strategies” such as extreme heat or ultraviolet light.
As for human cases of Creutzfeldt-Jakob not related to mad-cow disease, there has been an 85 percent increase nationally since 2002, when there were 260 cases compared with 481 in 2015, according to data from CDC.
Out on the landscape, CWD is also increasing and expanding its territory, although researchers are quick to say that this increase in Creutzfeldt-Jakob cases shouldn’t be construed as cause and effect.
How big a problem is it?
To date, no studies have shown that chronic wasting disease can actually be passed on to humans, as is the case with mad cow disease. In addition, no human cases of the chronic wasting disease have ever been identified.
Even so, health authorities are concerned about the possible risk to those who eat deer and elk from areas where CWD is established.
The US Centers for Disease Control and Prevention advises that the human health risks from CWD if any exist, are extremely low. However, as a precaution, the agency, as well as the World Health Organization (WHO), recommends that all products from animals known to be infected with any prion disease (for example, BSE in cattle, scrapie in sheep, and CWD in deer and elk) be excluded from the human food chain.
States with CWD management zones ask hunters to supply the head of a deer so it can be tested for CWD. If it is, they are advised not to eat any of the deer. While many hunters do get their animals tested, some don’t believe it’s a problem and doesn’t take advantage of the offer to have their animal tested.
Donald Davis, co-author of a recent report, “Basic Facts Surrounding CWD,” stresses the importance of relying on science instead of “often repeated pure speculation and rumor.” Not only is CWD a relatively rare disease, he said, but that in the past 20 years, fewer than 1 to 3 deer/elk per 1,000 tested positive for CWD nationwide.
However, CDC points out that while nationwide, the overall occurrence of CWD in free-ranging deer and elk is low, in several locations where the disease is established, infection rates may exceed 10 percent (1 in 10), and localized infection rates of more than 25 percent (1 in 4) have been reported.
“The infection rates among some captive deer can be much higher, with a rate of 79% (nearly 4 in 5) reported from at least one captive herd,” according to the CDC.
CWD can occur in captive game farms and also among wild, free-ranging deer and elk.
Davis also said that studies were done on humans in CWD-endemic areas, and where people eat large amounts of venison, show no more cases of the human form of brain disease than in areas without CWD.
The report also points out that in spite of the expenditure of over $100,000,000 of public funding, and thousands of animals killed, none of the prevention, control, or eradication methods employed by the various states since 1998 have been shown to be effective in either preventing increased prevalence of CWD or the increased geographic distribution.
However, a report on a CDC site about the potential transmission of CWD to humans points out that because CWD has occurred in a limited geographic area for decades, an adequate number of people may not have been exposed to the CWD agent to result in a clinically recognizable human disease.
The article includes information on research on people who have shown symptoms of the human variant form of CWD but comes up with no definite conclusions whether the people had actually been infected by a deer with CWD.
However, it warns that “the level and frequency of human exposure to the CWD agent may increase with the spread of CWD in the United States.”
It also points out that “provided sufficient exposure, the species barrier (between deer and humans) may not completely protect humans from animal prion diseases.”
And it calls for more research on this, saying that “because the number of studies seeking evidence for CWD transmission to humans is limited, more epidemiologic and laboratory studies should be conducted to monitor the possibility of such transmissions. “
How does it spread?
The disease is caused by misformed proteins, referred to as prions. It can be spread in various ways: saliva, feces, urine, and other bodily fluids — and even grasses, which have been shown to bind to, uptake and transport infectious prions.
These prions are persistent. In 1985 when the Colorado Division of Wildlife tried to eliminate CWD from a research facility by treating the soil with chlorine, removing the treated soil and applying an additional chlorine treatment before letting the facility remain vacant for more than a year, they were unsuccessful in eliminating CWD from the facility.
CWD and mad cow disease
Mad cow disease was first discovered in the United Kingdom in 1986. Originally, cows were considered the “dead-end host.” In other words, the disease would not spread to other species, including humans.
Cows were said to have become infected by eating “recycled” products such as sheep carcasses infected with scrapie, another brain disease, and also cow carcasses infected with mad-cow disease.
In January 1993, the mad-cow epidemic reached its peak with almost 1,000 new cases being reported each week.
Three years later, things went from bad to worse — then to worst when the first case of the variant human form of mad-cow disease, vCreutzfeldt-Jakob, or vCJD, was reported. The cause of this human form of brain disease is said to be from eating contaminated meat or other products from cattle (excluding dairy products) infected with mad-cow disease. It didn’t stop there: more people came down with the disease. All died.
So alarming was this that 4.5 million cows were butchered. The stench of piles of burning cows filled the air.
Trade was disrupted, and countries with cases of the mad-cow disease were banned from exporting their beef.
Since 1996, more than 230 vCJD cases have been identified in 12 countries, 178 of them in the United Kingdom, 27 in France, and four in the United States. Just last fall, a case of mad cow disease was confirmed in Scotland.
What about the hunters?
Even though some hunters will say they don’t have any worries about getting infected with CWD from eating an infected deer or elk or moose, they’ll also say they prefer to hunt in areas where CWD isn’t prevalent. Some don’t bother to get their deer tested.
“I won’t stop hunting,” said Kip Adams, conservation director for the Quality Deer Management Association (https://www.qdma.com). “But I will have any deer I kill tested (for CWD) before eating it or feeding it to my family.”
When he goes hunting, he’s very aware of where the CWD management areas are. Although he has hunted in those areas in Pennsylvania and other states, he makes sure he follows the states’ testing and monitoring protocols.
“If I shoot a deer I wouldn’t consume it until I get satisfactory test results,” he said. “It’s a hunter’s responsibility to do that.”
Washington state hunter Dick Klein quickly says he’s no expert on this but he has watched some shows about it. He feels fortunate that his state has no CWD problems but should he be invited to hunt in areas of states that do have CWD, he would quickly decline.
“I wouldn’t want to eat it (venison) or see my family or pets eat it,” he said. “I wouldn’t want to take any chances.”
In Minnesota, CWD numbers are worrisome. When it comes to the deer that were killed and turned in for testing, there were 14 positives and one suspect for 2018, an increase from recent years. That’s particularly worrisome because those 14 positives were part of the total 30 positives for 2016, 2017, and 2018.
“That’s not good,” said Erik Hildebrand, who said what’s also worrisome is that there were 3 positives found outside the southeast section of Minnesota’s CWD management zone. “That shows that it’s spreading,” he said.
Added to that concern is that deer densities are very high in that management zone. The best way to contain the disease is to reduce deer density — combat the disease and prevent it from spreading — is to allow more people to harvest more deer. in that zone. And that’s just what the state did.
“We wanted to get more samples,” he said, referring to the state’s decision to open up some special hunts in the zone.
Landowners also come into the picture, primarily because 90 to 95 percent of the land in the management zone is private property. With that in mind, the landowners can get a special permit.
Hunting is popular in Minnesota, which has about one-half million deer hunters.
While there currently are no human health concerns related to CWD, Hildebrand said a lot of the research is new. “Who knows what research will be forthcoming — and when.”
Hildebrand said that not only does testing gives hunters peace of mind, “it also helps us know how prevalent it is on the landscape.”
He’s quick to say that this is not just Department of Natural Resource’s problem. “This is everyone’s battle, including hunters, their families, and communities,” he said. “We all have to come together to help contain this disease.”
As for killing all of the deer to wipe out the disease, as some people have actually suggested: Hildebrand said that just isn’t feasible. Whereas in England, they could kill 4.5 million cattle when it was discovered that mad cow disease could spread to humans, those were domestic animals that could be rounded up.”
“It’s a wild population,” Adams said, referring to deer and elk. “It wouldn’t be possible.”
Mark Zabel, Associate Director of the Prion Research Center, Colorado State University, said that while no evidence exists to suggest that CWD zoonoses (the transmittal of a disease to humans from animals) has occurred, the possibility remains that it could happen, especially since only a few family and friends would eat the entire deer. That, in turn, would expose them to much higher doses of CWD prions than what humans ate during the mad-cow outbreak in England.
He also pointed out that one major concern is that, over a period of years, the deer disease could mutate as it passes from animal to animal, eventually producing prions that could infect people.
“If CWD is an emerging prion disease on the landscape, it may still be evolving through infected deer,” he said. “We have shown in the lab that deer prions can change and/or spontaneously arise. So it may be just a matter of time before a CWD prion emerges capable of infecting humans. Eating high doses of CWD prions, as hunters and their friends and family would eat, could stress the species barrier to a breaking point.”
This is why CDC and state officials urge hunters to get their deer tested and to refrain from eating them should they test positive for the disease.
What about roadkill?
“ It’s time to start eating roadkills,” says a recent headline in a Colorado publication. The article goes on to say that “the stereotyped hillbilly eating roadkill has been replaced by an environmental food conscientious middle-class urbanite.” A far cry from corporate agriculture, indeed.
Oregon has just recently given the thumbs-up to harvesting road-killed deer and elk, joining about 20 other states that allow people to take meat from animals killed by vehicles.
Kip Adams, conservation director for the Quality Deer Management Association, said he has eaten road kill in the past and would have no trouble eating it now.
“But if I were in a CWD management zone, I would have it tested,” he said. You need to pay attention to state regulations and follow guidelines.”
“I would exercise caution when eating roadkill cervids (deer, elk, and moose), said prion scientist Zabel:
“Assessing the health status of the animal at the time of death is nearly impossible. Indeed, evidence suggests that CWD prevalence in roadkill, and certainly prey of mountain lions, is higher, increasing the likelihood of eating prion-infected meat from road kill.”
Food safety tips
CDC advises hunters that “to minimize the risk for exposure to the CWD agent,” they should “consult with their state wildlife agencies to identify areas where CWD occurs and continue to follow the advice provided by public health and wildlife agencies.”
The agency also advises hunters to avoid eating meat from deer and elk that look sick or test positive for CWD. They should wear gloves when field-dressing carcasses, bone-out the meat from the animal, and minimize handling of brain and spinal cord tissues. As a precaution, they should avoid eating deer and elk tissues known to harbor the CWD agent (e.g., brain, spinal cord, eyes, spleen, tonsils, lymph nodes) from areas where CWD has been identified.
In addition, hunters should wash their hands and instruments thoroughly after field dressing is completed, and they should request that their animal is processed individually, without meat from other animals being added to the meat from their animal.
While out in the field, hunters should be on the lookout for animals that are unusually thin and exhibit behavior such as having trouble walking, as well as those acting tame around humans and allowing someone to approach them. Such circumstances should be reported to a state wildlife agency.
Matt Dunfee, the coordinator of the Chronic Wasting Disease Alliance, said that hunters in most CWD areas are required to turn in the heads of any deer, elk or moose they kill so it can be examined for signs of CWD.
“Hunters are massively helpful in providing surveillance for wildlife agencies,” he noted.
(Republished with permission of Food Safety News. To sign up for a free subscription to Food Safety News, click here.)