New science expands Chronic Wasting Disease debate
Chronic Wasting Disease has been a persistent issue among hunters and resource managers in all 25 states in which it now exists, including here in Wisconsin, since the first CWD positive elk was discovered in Colorado in 1967.
A positive doe found just west of Shell Lake in Washburn County in 2012 has rekindled discussion about CWD here in Wisconsin.
Initially the concern about CWD was focused on the health of the white tail deer population and the economic implications CWD could have on the deer hunting industry. New science has raised the possibility that we should be looking more closely at the potential effect CWD could have on human health, as well as hope that a new vaccine might stem the spread of CWD.
Wisconsin has more than 600,000 deer hunters who regularly harvest 300,000 to 400,000 deer annually, according to DNR Regional Wildlife Manager Mike Zeckmeister.
"Deer hunting ... generates more than $500 million in retail sales and over $1 billion in total impact to the state's economy," he said. "A healthy whitetail deer population is critical to the state's economy."
DNR CWD Wildlife Biologist Tim Marien said the state has spent roughly $43 million on the CWD program since the first whitetail tested positive in 2002. That money came from a combination of federal and state agencies including USDA and USFW. The most money was spent in 2003, $12.6 million, immediately after the initial detection of CWD in Wisconsin. The funding for surveillance, testing and research has decreased steadily since then to $600,000 in 2012.
If you do what a lot of folks do and just read the first couple of sentences of a paragraph and assume you've got the gist of what's being said, this is what you'll likely read in the first paragraph, of informational materials about the impact of CWD on human health, "there is no evidence that CWD poses a risk for humans," followed shortly by, "The World Health Organization has reviewed available scientific information and concluded that currently there is no evidence that CWD can be transmitted to humans." That's not exactly what the science is saying.
"I would not eat a deer that has not been tested (for CWD)," said retired veterinarian David Clausen, chairman of the Wisconsin Natural Resources Board.
Clausen said he is concerned that public access to information, including the latest science, isn't what it should be to enable hunters and other consumers to make informed decisions about CWD. He's also concerned government officials have been less than transparent in their decision-making process and that their priorities have been questionable when it came to preserving the resource and associated economy versus the health and well-being of citizens.
"We have a responsibility to be honest with the citizens of Wisconsin," he said. "If we are doing nothing to influence the progression of CWD, we need to say that. We need to be more up front about the likely ramifications of our inaction. We cannot continue to maintain to the public that we can manage this disease by simply watching it."
On March 20, 1996, British Health Secretary Stephen Dorrell rose before the House of Commons to inform colleagues that scientists had discovered a new variant of Creutzfeldt-Jakob disease (a fatal nervous system disease in humans), in 10 victims, and that they could not rule out a link to consumption of beef from cattle infected with bovine spongiform encephalopathy (BSE), also known as mad cow disease.
To date 217 cases of CJD have been diagnosed, mostly in the United Kingdom. The mad cow outbreak demonstrated that prion infections could cross species barriers between humans and cattle, increasing concern about the possible transmission to humans of a CWD another TSE.
Pursuant to the Federal Food, Drug, and Cosmetic Act, material from CWD positive deer and elk may not be used in any animal feed, and animal feed containing CWD positive material is considered adulterated and must be recalled from the market.
"Why isn't the same degree of caution apparently necessary regarding human consumption of CWD positive deer?" Clausen asked.
In Wisconsin, the Department of Health Services has maintained surveillance for human prion diseases since 2002.
"Hospitals and physicians who suspect a case are legally mandated to report those to us," said Jim Kazmierczak, state public health veterinarian.
It is DNR procedure to inform hunters who have had their deer tested for CWD, by phone, that their deer tested positive and that it is their recommendation, as well as that of the CDC and World Health Organization, that they do not eat that venison and instead dispose of it properly.
Beginning in 2004, if it was discovered that the hunter had already consumed venison from a contaminated deer for whatever reason, his or her name was referred to the DHS. A follow up call was made by DHS officials to conduct a brief interview to obtain the names of all of the people who had consumed venison from that particular contaminated deer (friends, family members etc.).
Those names are added to a registry of all hunters and other folks who have been identified as having eaten venison from a CWD positive deer. Today that registry consists of roughly 1,000 names.
"Based on the small numbers (consumers of venison) along with the long incubation period, we didn't think it (the registry) would be a very valuable tool for at least 10 or 20 years after we initiated it," said Kazmierczak.
Those names are regularly compared to the names of people who have been confirmed to have died from a human prion disease like CJD in the state of Wisconsin.
"The longer we don't find any venison eaters on our list of cases, the more sure we can be. To date, we don't have any incidences of human illnesses being related to CWD," confirmed Kazmierczak.
Scientists have been experimenting in laboratories around the world to try and better understand how prion diseases work. Prions are tenacious abnormal proteins and impressively resilient responsible for spreading CWD. They are typically transmitted between whitetail deer in saliva, urine and feces. They can also be transmitted from soil.
A team of scientists at the UW-Madison, led by assistant professor of soil science Joel Pedersen, proved prions have an affinity for a particular type of clay, montmorillonite, found in many common types of soil. Prions bind to the soil and can remain as infectious as those transferred directly by animals for at least two years.
This is just the kind of science Clausen thinks people should know about.
"We should be asking what are the department's (DNR) duties and responsibilities regarding increasing environmental contamination of soil and possibly plants with a disease agent that both CDC and WHO recommend people not consume," he said.
As a result of the Mad Cow outbreak in the UK, scientists made a significant discovery. Prion infections were found in extra neural lymphoreticular tissues (tonsils, lymph nodes and spleen). Until that discovery, health officials had only been looking for evidence of prion infections in the central nervous system (CNS), brain and spinal column.
Recent research by French scientist Vincent Beringue using human and ovine transgenic mice, demonstrated that lymphoreticular tissue may be up to seven times less resistant to cross-species infection with prions than brain tissue. Beringue's research also showed these mice lived normal life spans without showing any CNS symptoms but were none-the-less capable of transmitting disease when their splenic tissue was inoculated into other normal mice.
Because of this science and Clausen's bringing it to the attention of the DHS, if a prion disease is suspected in Wisconsin, "both neural and extra neural tissues would now be sent to the CDC for examination," said Kazmierczak.
CWD can cross the species barrier using a transmission mechanism called "serial passage." Serial passage is occurring between deer naturally in nature.
"The longer CWD stays on the ground and the father it spreads," said Clausen, "the more likely this type of thing is to happen." In other words, the more adept CWD will become at crossing the species barrier.
At UW-Madison, the brains of hamsters were injected with CWD prions from infected deer and did not get sick. Hamsters appeared to be immune to CWD. Then the brains of ferrets were injected with CWD prions from infected deer and they got the disease and died. When infected brain tissue from the diseased ferrets was injected into the hamster's brains, the hamsters got sick and died.
"So apparently CWD can make this end run around the species barrier," said Kazmierczak. "It adds to our concern regarding the transmission and mutation of CWD when diseased deer carcasses are scavenged by other animals like coyotes, raccoons, and bears, even crows. We need to be guarded and cautious when we talk about CWD, we just don't know."
Dr. John Mapletoft works for Pan-Provincial Vaccine Enterprise Inc, (PREVENT). The Canadian-based organization connects and coordinates experts from public health, academic organizations, research institutes, the vaccine industry and the investment community to focus on the development of vaccine technologies.
PREVENT researchers have been working on a promising injectable vaccine to prevent the spread CWD among farmed cervids.
"Our goal is to prevent the disease in animals that don't have it," Mapletoft said.
Tami Ryan, a manager in the wildlife health section for the DNR, remembered being involved in several public forums back in 2010 when work on the vaccine was getting started.
"It did not evolve to fruition because at the time there were some pretty significant challenges to overcome with getting a vaccine developed in Canada into the U.S.," she said. "About the same time, funding levels started to really decline (in Wisconsin) taking with it funds for research on CWD."
A viable vaccine must meet three standards: it must demonstrate an immune response, it must be proven safe, and it must work. The CWD vaccine works by using a very short piece of protein that mimics a piece of the misfolded prion.
"We have demonstrated that our vaccine does induce an immune response in multiple species and that the immune response is specific for the misfolded prion protein," said Mapletoft. "We also know it does not otherwise interact with or harm the brain."
According to Ryan, one key question is if animals already infected with CWD tare vaccinated, can they still be carriers? Would they still be sharing prions and shedding prions into the environment?
Mapletoft said the current vaccine is "primarily seen to be a preventative (vs. cure) situation, so animals that already have the disease are not the target. That's not to say it may not help them."
The first vaccine tests began earlier this year on elk in Wyoming and another will be starting later this year in Saskatchewan.
One of the difficulties of testing a CWD vaccine is the long incubation period of the disease. Each of these tests will take a minimum of two years to determine if the vaccine is working, unlike a flu vaccine, which can be tested in a matter of days or weeks. Results from the Wyoming test aren't expected until 2015.
"The vaccine has always been pursued with the idea that once the injectable vaccine is up and running and generating revenue, you would then have funds to proceed with a second generation oral vaccine which could be put out in the wild," said Mapletoft.
"Frankly when the news came out recently about these trials in Wyoming, we were quite surprised," said Ryan. "We'll be paying attention."