Chronic wasting disease (CWD) has been present in Fall River County for over 15 years. South Dakota Game Fish and Parks (GFP), reports 2001 as the first time an infected animal was found in Fall River County and in the State.
CWD is a unique disease. Unlike other ailments caused by viral, bacterial or fungal infections, CWD is caused by a mal-formed protein known as a prion.
Prions cause damage in animals' central nervous system because they can change 'normal' proteins in cells into other prions. These prions cause a host of symptoms according to GFP, including: "progressive loss of weight and body condition, behavioral changes, excessive salivation, increased drinking and urination, depression, loss of muscle control and eventual death."
CWD is part of a family of prion diseases known as Transmissible spongiform encephalopathies or TSEs. The 'spongiform' part of TSE references the microscopic holes in the brain caused by the prions. Encepholapathies are diseases that effect the structure or function of the brain.
Prion diseases are hard to control because of the prions unique durability in the environment. According to the Center for Disease Control (CDC), TSEs are "always fatal".
TSEs can be found in animals other than deer. Creutzfeldt-Jakob disease is a TSE found in humans, scrapie in sheep and Mad Cow disease effects mostly bovine populations.
According to Steve Griffin of GFP, there hasn't been a statewide survey in some time, however the agency does do its best to track the prevalence of the disease through voluntary hunter harvest samples of deer.
GFP takes a slightly more aggressive stance with elk. Prior to elk season opening, all hunters are requested to send a sample of harvested elk to GFP to test for CWD.
Griffin said part of the reason for the emphasis on elk is because the elk herd numbers in the State were low a few years ago.
Griffin said that compared to deer, elk tend to have a lower prevalence rate of CWD, around 1%-3%, saying some deer populations in Wyoming are at rates around 20%. He added that rates in elk can rise in herds that are confined to a certain area, like Wind Cave National Park or Custer State Park.
A digital map on GFPs website shows a large concentration of infected elk in and around Wind Cave. While some of this may be a result of a semi-enclosed herd, Greg Schroeder of Wind Cave added the Park is also taking a very aggressive stance on the disease, "this is a priority for us."
Schroeder said the Park is actively taking measures to sample its herd and added that part of the reason they appear to have more cases is simply because they are sampling more animals. He also said that any animal that shows symptoms is euthanized and its carcass is disposed of appropriately.
According to Griffin, a goal of deer and elk management is to make sure the rate of CWD doesn't climb to a point where the populations can't sustain themselves.
While there has never been a documented case of CWD transferring from deer or elk to humans, that doesn't mean it's impossible. "We don't know if humans can get it," said Griffin.
Mad Cow disease made the jump to some humans in the 1990s in Europe. Many of these cases were traced to the consumption of certain organ meats as well as the practice of feeding the remains of infected cattle to new cattle in the form of protein supplements.
"If you know you are hunting in a CWD area and harvest something that looks sickly, we suggest you get it tested and if it comes back positive, we suggest you don't eat that meat," said Griffin.
Spreading CWD is also a concern for GFP. Most of South Dakota's cases are found in the Southern Black Hills and all of them are within West-River. Griffin said hunters can play a key role in mitigating the spread, "proper carcass removal will assist in stopping the spread of this disease."
He suggested de-boning harvested animals and leaving the spinal column and brain in the field. He added if leaving the bones wasn't an option, certain landfills can properly dispose of the material.
A map of "Approved Big Game Disposal Sites" can be found at GFP's website along with additional information regarding CWD and other wildlife diseases.