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Chronic wasting disease affecting PA wildlife


Matthew Zollars, Contributing Writer

Mad Cow Disease is a neurological disease in cattle that essentially turns nerve tissue to mush.  According to the University of Michigan Medicine, people cannot get mad cow disease but, people can get a similar disease called variant Creutzfeldt-Jakob disease (vCJD) via consumption of nerve tissue of cattle infected with mad cow disease.  The symptoms of vCJD are dementia, psychotic behavior, problems moving parts of the body, and coma. The disease always results in death, and there is no cure.

According to the CDC, a new disease called Chronic Wasting Disease has been spreading throughout the United States.  CWD is a disease transmitted via prions and is known to exist in cervid (mammal of the deer family) populations. Prions are abnormal, pathogenic (disease-causing) agents that are highly transmissible and result in the abnormal folding of cellular proteins called prion proteins, located in the brain.  The abnormal folding of prion proteins causes brain damage, which is typically rapidly progressive and always fatal. A 2010 study conducted by Robert C. Holman found that "during 1979 through 2006, an estimated 6,917 deaths with CJD as a cause of death were reported in the United States.”

In a pamphlet from the USGS, it states that CWD was first found in Colorado in 1967 within a herd of mule deer used for research.  According to a 2015 study conducted by D.C. Bourne, CWD is one of a few diseases known as transmissible spongiform encephalopathies (TSE) and is the only known TSE of non-domesticated animals.  The Centers for Disease Control and Prevention states, “TSEs are a family of rare progressive neurodegenerative diseases that affect both humans and animals.”

The USGS determined that the disease-causing prions are present in feces, urine, saliva, and various other body tissues.  There is currently no known treatments or vaccines for CWD. CWD is fatal and years can pass before the animal exhibits symptoms.  According to the CDC as of 2019, cervids in twenty-four states in the USA have been found to carry CWD as well as Alberta and Saskatchewan, Canada.

Although found in cervids, it is unknown the extent to which CWD can be transmitted to other taxonomic groups.  According to Bourne, there are several known natural hosts of CWD: mule deer, white-tailed deer, Rocky Mountain elk, and moose.  To determine the extent to which CWD may be transmitted by different species, researchers have attempted to transmit CWD to several different species via oral and cerebral inoculation with varying success.  A 2008 study conducted by Christina J. Sigurdson stated that species such as cattle, goats, and sheep have been successful with intracerebral inoculation; twelve of fourteen inoculated cattle developed neurological diseases after twenty-two months.  The USGS states that currently there are no known cases of CWD infection in humans; epidemiological studies fail to link prion-based diseases in hunters or young people in North America and CWD.

CWD can have a wide variety of adverse effects on humans and the environment.  According to the USGS, “conservation efforts conducted by State agencies that rely on hunting as a source of revenue could be negatively affected.”  The ecological implications have profound potential; changes in cervid populations could affect the balance of the ecosystem. Many businesses rely on hunting activity, which would suffer from a decrease in hunter numbers.

The CDC recommends not consuming or handling meat from deer or elk that appear sick or are acting strangely.  The CDC also highly recommends having deer and elk that were harvested in areas containing CWD, tested for the presence of CWD.

CWD has been spreading relatively rapidly in the United States.  Although there have been no known cases of humans becoming infected, this should not be taken lightly as studies have shown that some livestock species are susceptible to CWD.  Preventative measures should be made to prevent the transmission to humans; people should avoid contact with deer in known CWD areas as well as having meat tested for the presence of CWD to avoid consumption of possible prions.  Local hunters should be wary when field-dressing and processing deer meat and should use rubber gloves especially when coming into contact with spinal and brain tissue to prevent possible transmission.