Chronic wasting disease still keeps secrets about itself that researchers in Missouri and elsewhere are hoping to discover, which could help people better understand how the deadly deer disease spreads.
The Missouri Department of Conservation announced last week it has added regulations to the state's wildlife code as part of efforts to slow the spread of chronic wasting disease, or CWD.
New regulations that take effect Feb. 29 will restrict the transportation and disposal of deer carcasses into and within the state — carcasses being a way for the disease to be carried from one location to another.
CWD has no vaccine or cure and eventually kills all deer infected by the prions that cause it.
Prions are bits of infectious protein that cause other normal forms of prion proteins found in mammals and most animals to become misshapen, said Jasmine Batten, an MDC research scientist and wildlife disease coordinator.
As those proteins become misshapen, "they can't function normally," Batten said. "The body can't eliminate them. They congregate, and they actually cause neurological degeneration and damage."
She said there's no evidence CWD affects humans, but being lethal to deer, Missouri's Conservation Department describes CWD as a threat to deer hunting and watching traditions and to the state's hunting economy, which "gives a $1 billion annual boost to the state and local economies."
The Centers for Disease Control and Prevention does caution that people should not eat an animal that tests positive for the disease.
"Since we've found CWD in our free-ranging deer in 2012, (MDC) has dramatically increased our surveillance from 5,500 deer a year to over 30,000. That surveillance itself is indeed research," Batten said about the focus of MDC's work with CWD, " find the disease, take steps to slow the spread, monitor changes and provide stakeholders with relevant information."
"Our biggest goal in the last couple of years has been stopping the spread of CWD. We want to keep it rare in the state so that down the road, if we do have new technology and new science, we're in a position to be able to do something about it, versus if the disease was wildly out of control," she said.
As of July 1, Missouri has counted 116 cases of CWD in free-ranging deer in 16 counties — including one case in Cole County, in the 2014-15 testing year, according to the MDC.
Most of the cases in the state have been detected since 2017, with Macon, Adair, Franklin and Ste. Genevieve counties having the most.
The first cases in the state were detected in 2010 and 2011, "in captive deer at private big-game breeding and hunting facilities in Linn and Macon counties. A total of 11 cases were confirmed in captive deer at the facilities," according to the MDC.
In Missouri, CWD is in isolated pockets in small areas, where in 25-100 square miles, less than 5 percent of deer are infected — whereas in Wisconsin, there are areas of the southwest part of that state where at least 50 percent of adult male deer are infected, she said.
"CWD is a very slow-spreading disease, so we've really not been in this game for very many years. A lot of the places that we've found (CWD), we've just been working on it for a year or two, so it's going to take a while for us to be able to look at that data and see what we can learn about the disease," Batten said.
That's not to say Missouri is not involved in applied research into understanding CWD, beyond just monitoring its spread.
Batten said tissue samples from deer that test positive for CWD are being provided to Colorado State University, where there's a prion research laboratory that's working to identify different strains of the disease that are in North America, in order to potentially better track how the disease has spread.
"The hope is that with that research, we can kind of learn more about the disease in Missouri, what are the characteristics — do we have different versions of it that could have management implications," she said.
"It's very expensive and difficult work to do. It has to be done in a prion-certified lab," she said of such work that Colorado State is doing.
Batten said prion research has to be done at labs with Biosafety Level 3 certification — second-highest out of four levels of biological lab safety.
BSL-3 labs have workers under medical surveillance, and in addition to the required safety gear for workers, the labs themselves must be built so the entrance is "through two sets of self-closing and locking doors," and "exhaust air cannot be recirculated, and the laboratory must have sustained directional airflow by drawing air into the laboratory from clean areas towards potentially contaminated areas," according to the CDC.
Closer to home than Colorado, Batten said Missouri is fortunate to have such a certified lab at the University of Missouri, where "this year, (MDC is) moving toward them doing all of our testing."
Batten said it was MU's lab that contacted the MDC, and the partnership means faster-turnaround times for hunters because of increased testing capacity — testing that could be done at a Department of Agriculture lab in Springfield, but that lab doesn't have the capacity to keep up with the annual volume of tests, she said.
She said hunters have an interest in faster turnaround times for testing because, anecdotally, there's "growing interest from some hunters to have their deer tested before they consume the meat" — stemming from the CDC's recommended precaution to not consume animals that test positive.
Also, if getting the results takes a month because of the volume of tests to be analyzed, a hunter in that time might have already paid for their deer to be processed, Batten said.
She added some meat processors have already taken it upon themselves to hold quarters or meat of tested-deer before processing it and making sausage — to avoid the possibility of discovering after the fact some meat contaminated with CWD was processed and sent to multiple people.
"We're really interested in working with (MU) on exploring testing technology, generally — looking for ways to deal with this capacity, ways to speed the test up and ultimately, hopefully, ways to detect the disease earlier in animals," Batten said.
She said the current standard is to test the lymph nodes of deer, but detection only works after CWD has been in the animal for months.
Some testing in the state is mandatory for hunters, if deer are harvested from certain areas on Nov. 16 or 17 this year. That testing is free, and results are available online.
Voluntary testing is also available throughout the season, and that sampling is free at certain locations.
"Hunters can also have harvested deer tested for CWD by contacting the State-Federal Cooperative Veterinary Diagnostic Laboratory in Springfield at (417) 895-6861, or the University of Missouri Veterinary Medicine Diagnostic Laboratory in Columbia at (573) 882-6811. There are fees for CWD testing at these facilities," according to the MDC.
Batten said current testing technology, which makes it difficult to test for prions at low concentrations, also makes it difficult to determine exactly how CWD spreads — "where those prions end up in the environment, and how concentrated they are, and if they're concentrated enough for deer to get the disease."
Beyond spread through direct contact between deer, the prions that cause CWD can enter the environment through deer saliva and excrement, and remain infectious for years, as well as bind to soil when a deer carcass rots in one spot, Batten said. "We're really concerned about carcass movement for that same reason" of wanting to avoid having prions accumulate in one location, she said.
Plants can absorb the prions up through their roots and deposit them in their leaves, but it remains to be seen whether deer can be infected that way, she said — the subject of research at the National Wildlife Health Center in Madison, Wisconsin.
Batten added there's no evidence of CWD spreading through insects, and while the prions can stay infectious after passage through a deer predator's digestive tract, that doesn't seem to be a driving force, given the rate of spread.
"We do have some grant proposals out and are in conversations about that general topic — how can we work together to advance testing technology to benefit both research and hunters," she said of the work with MU.
Though there's a renewed interest in federal funding that could open possibilities, there's not a lot of federal money going toward CWD research, she said. "Throughout most of the country, most of the funding is coming from state agencies or universities," she said.
"Here in Missouri, right now at least, we are funding all of the testing work that we're doing, pretty much through our state agency," Batten said, and that means a contract for paying MU for its diagnostic services.
What would delivery of a cure look like, if one were to be found for CWD?
Batten said a prion vaccine is pretty far off, and "it's difficult with free-ranging wildlife to do vaccinations," but there are precedents for it, such as dropping rabies vaccines that animals can come along and eat.
"It's not something that's never been done," Batten said.