In the 1960s, a new disease called chronic wasting disease appeared in Colorado and quickly spread through populations in surrounding states. Since then, new instances of the disease have been popping up – sometimes widespread, sometimes relatively confined – but always fatal. It is this 100% fatality rate and the current absence of a cure that has conservationists, hunters, and scientists alike on edge.
So what is chronic wasting disease? Which organisms can contract it? Most importantly, which measures are being taken to stop it? This brief look into chronic wasting disease and a potential new weapon against it aims to answer these questions.
What Is CWD?
Chronic wasting disease, otherwise known as CWD, is a contagious disease that affects members of the deer family. It is a transmissible spongiform encephalopathy, or TSE, similar to bovine spongiform encephalopathy (BSE), or mad cow disease, in cattle. Other TSEs include scrapie, which affects sheep and goats, and Creutzfeldt-Jakob disease in humans.
TSEs are a rare class of brain diseases primarily associated with an accumulation of abnormal prion proteins. Commonly found on the surfaces of many cells, prion proteins can unfold in the presence of TSE diseases like CWD, and clump in the brain. After some time, accumulations of clumped prions can form in the spinal column and the central nervous system, severely impeding its function. CWD is ultimately fatal to the host animal.
How Does CWD Spread?
CWD affects free-ranging deer, moose, and elk throughout North America, South Korea, and Northern Europe. When these free-ranging animals move about their environment, they shed prions via feces, urine, and saliva. After death, the decaying carcasses of animals infected by CWD continue to leach prions into the soil and the surrounding water supply.
Other organisms that encounter prions from a live animal, its secretions, or via the environmental exposure to the prions shed by deceased animals, can contract CWD. While it is not thought that humans or other organisms can contract the disease, the spread of CWD is still a concern. Throughout the past sixty years, the disease has spread to three continents and nearly 30 states.
Reducing the Impact of CWD
Since animals with CWD are often asymptomatic for nearly two years, managing the live animal-to-live-animal spread among wild deer populations has proven difficult. Similarly, the fact that prions can continue to exist on plant matter and soil for years while retaining the ability to infect additional animals has made combating the spread a challenge. However, researchers have identified a new way to reduce the possibility of animals contracting the disease from the soil.
Although prions are unstable, unfolded proteins, they still perform one of the most basic functions of proteins within a live animal – binding. Recent findings suggest that humic acid, a common soil organic matter compound, can bind to prions and reduce their infectivity. Researchers have increased humic acid concentrations in mice, effectively reducing the impact and infectivity of these prions.
Continuing the Fight Against CWD
Further research into the protein stability of CWD and other TSE prions could implicate other organic compounds that may bind and impact the transmission of the disease.
Reducing the amount of infectious soil by manipulating the concentrations of such compounds could go a long way to preventing the spread of CWD before it affects other populations. Much more research about CWD is needed, but the future is beginning to look a bit more positive for the ever-increasing number of animals at risk for infection.