Prescribed cure may accelerate the spread of a deadly disease
If a contagious and deadly brain rot spread by deer and elk threatens people who eat venison, can controlled burns that boost deer, elk and moose populations slow the spread of the illness?
The controlled burn prescription, advanced by Colorado State University immunologist Mark Zabel, is soon to be tested on National Park Service land in Arkansas and Colorado, Carl Zimmer of The New York Times reported on June 26, 2017.
The deadly brain rot is variant Creutzfeld-Jakob Disease, believed to have killed at least 231 people worldwide, 177 of them in Britain.
Sheep, cannibals, & mad cow disease
Called vCJD for short, variant Creutzfeld-Jakob Disease is spread through ingestion or other absorption of prions, the misfolded scraps of cellular protein associated with Chronic Wasting Disease (CWD) in deer, elk, and moose; scrapie in sheep; kuru among cannibals in Papua New Guinea; and bovine spongiform encephalopathy in cattle (BSE), better known as “mad cow disease.”
Zabel and his former graduate student Aimee Ortega outlined the case for trying to stop CWD with controlled burns in the September 2016 edition of Microbiology & Molecular Biology Reviews.
Bucks & dough
State and provincial wildlife agencies, funded in large part by the sale of licenses to hunt deer and elk, along with owners and managers of private hunting preserves, appear to be leaping for the idea like a buck in hot pursuit of a doe.
New research meanwhile threatens their bucks and dough, if hunters heed the implications of recent cruel monkey experiments which might be rationalized––or not––by the potential of the findings for reducing both animal and human suffering.
Much depends on whether hunters are persuaded to stop hunting in recognition of the risk that venison-eaters might develop vCJD.
“Makes Swiss cheese of your brain”
As Quality Deer Management chief executive Brian Murphy recently explained to Brian Bloom of the Jackson, Mississippi Clarion Ledger, CWD (and by implication vCJD) “ultimately eats holes in your brain. It slowly makes Swiss cheese of your brain.”
The possibility that ingested CWD prions might trigger vCJD has long been recognized. The Archives of Neurology in October 2001 reported about the deaths of three deer hunters and frequent venison eaters, residents of Maine, Oklahoma, and Utah, respectively, all were under age 30, who developed vCJD between 1997 and 2000.
After CWD was found a few months later among deer in Wisconsin, Milwaukee Journal-Sentinel staff reporter John Fauber recalled that Minneapolis computer engineer Kevin Boss, 39, a deer hunter and venison eater who hunted in Wisconsin, had developed an apparent case of vCJD in 1994, dying two years later.
Does risk make hunters quit?
Surveying 405 Wisconsin deer hunters, the St. Norbert College Survey Center in Hayward, Wisconsin, reported that 36% said they might quit hunting where CWD was believed to exist.
Not clear, since hunting participation has declined around the U.S. and Canada, is whether fear of vCJD has actually contributed. In 2001, however, before the discovery of CWD in Wisconsin, the state Department of Natural Resources sold more than 688,000 licenses to hunt deer with firearms. The Wisconsin DNR sold only 599,000 licenses to hunt deer with firearms in 2016, the lowest total since 1976.
The effect of warnings about vCJD is currently getting another test. The Health Products & Food Branch of Health Canada warned on April 26, 2017 that “the most prudent approach is to consider that CWD has the potential to infect humans,” and recommended “avoiding consumption of foods from known infected or any diseased animals, and taking precautions when handling cervid carcasses.” Cervids are deer, elk, and moose.
Continued the Health Products & Food Branch of Health Canada advisory, “There is also the potential for Canadians to be exposed to cervids through farming (including veterinary services), slaughter, and [antler] velvet harvest, as well as through field dressing of hunted animals, preparing trophies and/or the use of cervid-derived materials (e.g., urine) as hunting lures.”
Beginning in 2009, working at the Alberta Prion Research Institute at the University of Calgary, Canadian Food Inspection Agency researcher Stefanie Czub “exposed 18 macaques to CWD in a variety of ways: by injecting infected material into the brain; through contact with skin; by feeding them infected meat; and intravenously,” explained Andrew Nikiforuk, contributing editor to The Tyee, a Vancouver-based news magazine.
“To date,” Nikforuk continued, “three of five macaques fed a total of five kilograms of infected white tail deer meat over a three-year period tested positive for chronic wasting disease. That’s the human equivalent of eating a seven-ounce steak per month. Two of three macaques fed deer meat developed the symptoms of the disease, including anxiety, ataxia and tremors. One animal lost a third of its body weight in a six-month period. Two macaques that had infected matter inserted into their brains via steel wire also developed the disease. Incubation times ranged from 4.5 to 6.9 years.”
Game farms spread the disease
The Canadian advocacy organization Alliance for Public Wildlife told Nikforuk that Canadian hunters and their familes consume “between 7,000 and 15,000 CWD-infected animals every year, and that percentage is rising by 20% a year” as CWD spreads.
“Ninety infected game farms in Saskatchewan spread this new and emerging disease all over that province, and the level of testing there is still pathetic,” Alberta hunter and independent prion researcher Darrel Rowledge fumed to Nikforuk.
“Farming cervids caused this whole thing,” Rowledge added, “exactly as some of the world’s best scientists predicted,” notably University of Calgary professor emeritus professor emeritus Valerius Geist, who warned almost from the beginning of game farming in Canada that transporting deer and elk to be hunted in captivity could import CWD.
Buying & selling
Recalled Nikforuk, “CWD first emerged among captive deer at a [Colorado State University] wildlife research facility in 1967. Researchers didn’t realize that the mysterious killer was caused by prions until 1978.
“Since then,” Nikforuk summarized, “the disease has spread via trucks as the game farm industry traded and sold elk and deer across North America. Scientists confirmed the first case on a game farm in Saskatchewan in 1996, and later traced the origin of the outbreak to infected CWD animals from a U.S. game farm,” specifically in South Dakota.
“Alberta soon confirmed CWD infections as well,” also traced to South Dakota game farms, “and in 2004 wildlife experts confirmed repeated transfers of the highly infectious disease from commercial farms into wild deer and elk populations in Canada.
“No safe dose”
“Since then the disease has spread like a boreal wildfire,” Nikforuk wrote. “CWD has now been confirmed in 24 states and has caused havoc in states that traditionally prize the hunting of wild deer such as Wisconsin and Pennsylvania.”
The Challenge of CWD: Insidious and Dire, a handout published by the Alliance for Public Wildlife, warns that “There is no safe dose of CWD prions. Infection is possible with very low doses. Unlike other prion diseases,” such as scrapie and mad cow disease, “CWD can be spread from animal to animal via urine, feces and saliva. It is the most contagious of all prion diseases.
“CWD is nearly indestructible,” the handout continues. “ It can remain infectious in the environment for long periods of time, particularly in clay-based soils, which incredibly increase the agent’s infectivity up to 680 times. Prions can withstand an assault of disinfectants, detergents, radiation, freezing and even incineration.
Even scarier, the handout says, “CWD can be picked up by plants and remain infectious. Recent studies have shown that plants as varied as alfalfa, barley and tomato can absorb prions and serve as an infectious source for mice.”
“Worst outbreaks are in the Rockies”
Reported Carl Zimmer of The New York Times on June 26, 2017, introducing Mark Zabel and his scheme to fight CWD with controlled burns,
“Direct contact, it turns out, may not be the only way in which prions are transmitted. Sick animals and cadavers spread prions across the landscape. Plants and soil may remain coated with deformed proteins for years, perhaps even decades. If deer got sick only by direct contact,” Zimmer wrote, “you would expect the outbreak to be most severe in the Midwest, where populations are densest. But some of the worst outbreaks are in the Rocky Mountains, where there are fewer animals.”
Zabel, therefore, “now suspects that the only way to rid the land of them is to set controlled fires,” Zimmer summarized.
Speaking for themselves
Wrote Zabel and Ortega in their Microbiology & Molecular Biology Reviews article “The Ecology of Prions,” “Controlled burning of landscapes in North America helps to mitigate ﬁre danger in drought-stricken areas, in some of which CWD is endemic. Burning of plants, feces, and topsoil in these areas may reduce the low-level prion infectivity present in these areas,” even though “the burn temperature and duration are certainly much lower” than necessary to destroy a prion.
Asserting that “Prescribed burning may sufficiently lower prion titers on landscapes to at least impede the indirect transmission of CWD,” without really explaining how, Zabel and Ortega suggested that burning, “Combined with directed hunter harvests, systematic culling, and targeted implementation of CWD vaccines,” which do yet yet exist but are in development, “we may be able to stem the slow but steady spread of CWD across the landscape.”
Boosting the deer population
Apart from the question of whether the burning temperature will be anywhere near the temperature required to destroy prions, the Zabel/Ortega argument as a whole suspiciously resembles a traditional strategy for increasing the deer population for the benefit of hunters.
That Zabel and Ortega are advancing their case from Colorado State University seems especially odd in view of the Colorado experience with both wildfires and CWD over the past 50 years. The wildfire history of Colorado over this time is documented here:
4-5 times more fire––and more CWD
CWD was first identified in Colorado in 1967, the year after what was then a record wildfire year for the state, with 673 fires burning 7,361 acres.
Since then, the average number of wildfires and acres burned per year have increased steadily, to an average of 2,973 fires & 41,430 acres burned per year in 2000-2009, while CWD has run amok.
Despite the rapidly increasing frequency and intensity of wildfires, fire cumulatively burning acreage equal to more than 15% of the whole of Colorado has utterly failed to control the spread of CWD. To the contrary, fires may have accelerated the spread of CWD, for example by causing infected herds to migrate from fire zones into proximity to other herds, and then by attracting uninfected herds into post-fire regrowth areas shared with infected animals.
If Zabel and Ortega are correct in their theory that deer and elk become infected chiefly by ingesting prions taken up by plants, wildfires might have stimulated the ingestion of prions by stimulating the new growth that deer, elk, and moose most like to eat.
Setting fires to promote the regrowth that deer favor, in particular, is a tactic practiced since pre-Columbian times.
Explains the Pennsylvania Game Commission web site, under the heading Controlled Burns Improve Hunting Opportunity, “Who were the first prescribed burners in Pennsylvania? The Seneca, Susquehannock, Delaware and other tribes. Why did they burn? To improve hunting grounds and game populations.
“Controlled burning improves wildlife habitat and hunting opportunity by increasing soft mast production in shrubs like blueberry, huckleberry, and blackberry; rejuvenating succulent browse plants preferred by deer and elk; promoting oak habitats and their vitally important acorns; [and by] maintaining grasses and broadleaf plants sought by brooding turkeys and grouse.”
Use of controlled burns to boost deer populations to encourage the sale of hunting licenses has come under increasing criticism since circa 2000 because of the growing perception in many regions that having too many deer presents a traffic hazard, inhibits the growth of the biggest bucks, harms bird habitat, and — most of all — because of increasing concern about “controlled” fires becoming wildfires.
In response, however, private property owners who hunt or lease land for hunting have over the same time formed many “controlled burn groups” to boost deer population regardless of state management policy.
Under pressure to stop controlled burns, chiefly as a fire hazard, fire advocates have advanced many pretexts to continue, including tick control and control of “noxious” weeds and non-native plants.
“Raises significant questions”
Since prescribed burns will tend to increase the deer population willy-nilly, since most of the burning is highly unlikely to destroy prions, and since more deer tends to increase the risk of infectious disease transmission (even if the transmission only occurs through cervid practices such as gnawing bones for calcium), more burning appears to more resemble a prescription for spreading CWD than a prescription for actually controlling it.
Commented Program for Monitoring Emerging Diseases moderator Martin Hugh-Jones, DVM, Ph.D., MPH, “Taking a flame thrower to an obviously contaminated site may well do some good, but to a suspected meadow or normal deer habitat raises significant questions. If fires are to help control CWD, maybe their preferred site would be on deer breeding farms with good security. Thus quarantined deer could be moved to ‘clean’ pasture while the ‘contaminated’ pasture is burnt,” with “boundary fencing high enough to prevent the breeding deer from escaping and wild deer from gaining entry.”
“Directed hunter harvests” & culling
The other major parts of the Zabel/Ortega prescription, “directed hunter harvests” and “systematic culling,” have no more history of success.
Killing all cattle in Britain who might have been exposed to either mad cow disease or scrapie, a total of 4.4 million between 1986 and 1998, did not entirely eliminate bovine spongiform encephalopathy, and that was logistically much easier than exterminating wild cervids distributed over regions that are many times bigger than Britain.
After CWD was first identified in Canadian elk, the Canadian Food Inspection Agency killed more than 8,000 animals at cost of $30 million, to no avail. Colorado officials killed 10,000 deer to try to contain CWD just in 2001, but 16 years later it remains endemic in much of the state.