Scientists still don't know whether eating that deer in the process of developing prion-caused brain and body wasting disease someone recently hunted can be passed to humans. The same goes for any other animal eaten historically by humans.
New research from David Westaway, Ph.D., of the University of Alberta and Jiri Safar, Ph.D., Case Western Reserve University School of Medicine has uncovered a quality control mechanism in brain cells that may help keep deadly neurological diseases in check for months or years, says a January 16, 2014 news release, "Prion discovery could help keep deadly brain diseases in check." The prion-caused brain illnesses are caused by the conversion of normal cellular prion proteins into the diseased form.
A new prion discovery could help keep deadly brain diseases in check. Latest research from David Westaway, PhD, of the University of Alberta and Jiri Safar, PhD, Case Western Reserve University School of Medicine has uncovered a quality control mechanism in brain cells that may help keep deadly neurological diseases in check for months or years.
The findings, published in The Journal of Clinical Investigation, "present a breakthrough in understanding the secret life of prion molecules in the brain and may offer a new way to treat prion diseases," said Westaway, Director of the Centre for Prions and Protein Folding Diseases and Professor of Neurology in the Faculty of Medicine and Dentistry at the University of Alberta.
Prion diseases lead to incurable neurodegenerative disorders such as Creutzfeldt-Jakob disease in humans, mad cow disease (Bovine Spongiform Encephalopathy) and chronic wasting disease in deer and elk
For years, scientists have been perplexed by two unexplained characteristics of prion infections: vastly differing asymptomatic periods lasting up to five decades and when symptoms do arise, greatly varying accumulation of the diseased proteins. In striking contrast, test tube prions replicate rapidly, and in a matter of days reach levels found in brains in the final stage of the disease.
"Our study investigated the molecular mechanism of this intriguing puzzle," said Safar, according to the news release. Safar is Co-Director of the National Prion Disease Pathology Surveillance Center and Associate Professor in Departments of Pathology and Neurology in Case Western Reserve University School of Medicine.
In probing these mysteries, Westaway, Safar, their teams and other collaborating researchers in the U.S., Italy and the Netherlands studied a molecule called the 'shadow of the prion protein.'
"Dramatic changes in this shadow protein led us to expand our view to include the normal prion protein itself," said Westaway. "This is a crucial molecule in brain cells because it is pirated as the raw material to make diseased prion proteins."
The production and degradation of the normal prion protein had previously received little attention because it was assumed its production pipeline did not vary. "The puzzle of the long asymptomatic time period required sorting out the different types of prion protein molecules. Our laboratory developed new techniques to tease out these subtle differences in shape," Safar said in the news release.
The researchers discovered a marked drop in the amount of the normal prion protein in eight different types of prion diseases. Strikingly, this drop occurred months or years before the animal models showed tell-tale clinical symptoms of the brain disease.
"Our belief is that cells under prion attack are smarter than we once thought," Westaway explained in the news release. "They not only sense the molecular piracy by the diseased proteins, but they also adopt a simple and at least partly effective protective response – they minimize the amount raw material from the pipeline for prion production."
"We believe we can kill two birds with one stone, because the normal prion protein is also a receptor for toxicity. Augmenting this natural protective response may be a preferred route to cure prion infections," Safar added in the news release. The study's discovery of a natural protective response can also explain the long latency period in other more common neurodegenerative diseases.
"The pre-clinical phase of the disease—before it shows symptoms—is when you want to set things straight. We may be able to take a slow disease and bring it to a complete standstill," Westaway said in the news release. "Since some scientists believe the normal prion protein is an accessory in the brain cell death of Alzheimer's disease, gaining a new understanding of rare yet lethal prion diseases may provoke fresh insights into human dementias."
The study's funding came from the Alberta Prion Research Institute, Alberta Innovates-Health Solutions, the Canada Foundation for Innovation, the US National Institutes of Health and Centers for Disease Control and Prevention, the University Health Network, and the Charles S. Britton Fund.
Controlling wasting disease in deer
Chronic wasting disease, the deer-equivalent of mad cow disease, has crept across the U.S. landscape from west to east. It appeared first in captive mule deer in Colorado in the late 1960s. By 1981, it had escaped to the wild. It reached the Midwest by 2002. Little is known about its potential to infect humans.
Now researchers at the University of Illinois offer a first look at the long-term effectiveness of the practice of culling deer in areas affected by CWD to keep the disease in check. Their study appears in the journal Preventive Veterinary Medicine.
Each year, the Illinois Department of Natural Resources tests 7,000 (hunted, culled or incidentally killed) deer for CWD infection, conducts aerial surveillance to see where deer congregate and sends in sharpshooters to cull deer at the sites with disease, said Jan Novakofski, a professor of animal sciences at the University of Illinois and an author of the study, according to the October 21, 2013 news release, "Targeted culling of deer controls disease with little effect on hunting."
"We know a lot about how far deer typically move," he said. "If they're sick, they're going to spread the disease that far. So if you find a deer that's sick, you draw that small circle and you shoot there." He called this approach "a textbook scientific strategy for control. You reduce contact and you reduce the spread of infection with the smallest overall impact on healthy deer."
Novakofski and his colleagues at the Illinois Natural History Survey (part of the Prairie Research Institute at the U. of I.) found that the strategy worked: The prevalence of CWD in tested Illinois deer remained at about 1 percent from 2002 to 2012.
The team also found that hunters were killing more deer each year in each region of the state (north, central and south) regardless of CWD and CWD management. Statewide, the number of deer killed by hunters went from 147,830 in 2001, before the appearance of CWD, to 181,451 in 2012.
The only exception: Two counties out of 10 with cases of CWD saw a reduction in hunter harvest over the same period."We wanted to know whether Illinois hunters have fewer deer to hunt now than they did before CWD," said Nohra Mateus-Pinilla, a wildlife veterinary epidemiologist at the INHS who led the study with postdoctoral researcher Mary Beth Manjerovic. "We found that hunter harvest has increased, and the prevalence of CWD has been maintained at low levels for 10 years in Illinois."
This finding answers a long-time complaint by some hunters that the culling of deer makes it harder for them to find deer to shoot, Novakofski said in the news release. "Since 2001, hunter harvest of deer has increased similarly in the northern region of Illinois, where CWD occurs, and the rest of the state, where there is no disease or sharpshooting," he explained. In the two Illinois counties with fewer deer, "the reductions were 11 to 20 percent," Manjerovic recalled, according to the news release.
The team compared the Illinois experience with that of Wisconsin, which changed its CWD-management strategy from one that relied on culling to one that consisted primarily of allowing hunters to thin deer herds, the researchers said. Wisconsin saw a striking increase of infection in CWD-tested deer after it did that, the team found.
"In the early years in Wisconsin, (CWD prevalence) was still about 1 percent, just as it was in Illinois," Manjerovic said in the news release. "Then the strategy changed. Since 2007, CWD prevalence has increased to about 5 percent."
"We can't find an environmental or other variable that explains the increase in prevalence except a change in management," Novakofski said, according to the news release. The numbers may not seem alarming to some, said postdoctoral researcher and co-author Michelle Green. But the trend is of concern, she said.
"CWD is a prion disease (like mad cow disease) and it's 100 percent fatal
There's no current way that we can actually make the deer better, so it's important that we keep it from spreading too far throughout the population," she said. "And then there's also the connection to mad cow disease. We don't have enough information yet to really understand what the impact to human health could be."
"We all hope that there is never a case of chronic wasting disease in humans. We all hope that it never spreads to people or agricultural animals," Novakofski said in the news release. "If it ever does, the investment in maintaining prevalence at a low level in Illinois will be repaid a thousand-fold."