Wisconsin Hunters Asked to Help Fight Chronic Wasting Disease

Wisconsin’s deer hunting season has been expanded in recent years, with the discovery of several new cases of Chronic Wasting Disease in the state’s deer population. The special hunts are meant to eradicate deer in Iowa, Dane and Sauk Counties – where all the cases of Chronic Wasting Disease have been found so far – in hopes that the disease will be wiped out before spreading further.

Although deer from almost every county in Wisconsin will be tested for infection, resources are not available to test every deer killed. That prospect does not bode well for the hunting season, which contributes a large measure to Wisconsin’s economy. Additionally, a smaller deer harvest this fall could mean a larger deer population – and more Chronic Wasting Disease – next spring.

Why Should We Worry About Chronic Wasting Disease?
Chronic Wasting Disease (CWD) is related to bovine spongiform encephalopathy (BSE, or “mad cow disease”), which has been found in European cattle in recent years. And BSE has been linked to a new variant of Creutzfeld-Jakob Disease, which research suggests likely resulted from human consumption of beef from cattle infected with BSE. CWD, BSE and the new variant of Creutzfeld-Jakob Disease (vCJD) are all classified as transmissible spongiform encephalopathies (TSEs), a group of rare degenerative brain disorders characterized by tiny holes that give the brain a "spongy" appearance. Confirmed diagnosis can only be made by a biopsy of the brain tissue, although some health care providers also use spinal fluid samples, electroencephalograms, and magnetic resonance machines to help in their diagnosis.

Research suggests that TSEs are caused by an abnormal version of a protein called a prion. Prion proteins occur in both a normal form, which is a harmless protein found in the body's cells, and in an infectious form, which causes disease. The harmless and infectious forms of the prion protein are nearly identical, but the infectious forms have been described as “misfolded proteins” or “mutant proteins” and experts say they accumulate in the brain, lymph nodes and spinal cord.

According to Mohammad Almoujahed, MD, Assistant Professor of Medicine in the Medical College of Wisconsin’s Division of Infectious Diseases, "Chronic Wasting Disease has been known to occur in deer and elk in the US for decades, but ongoing surveillance did not show any human case of the disease and there is no scientific evidence that CWD can infect humans. This differs from vCJD in that the link between vCJD and BSE was established by strong epidemiologic and laboratory evidence."

TSEs Uncommon But Frightening
Creutzfeldt-Jakob disease (CJD) is the most well-known of the human TSEs. It is a rare type of dementia that affects about one in every one million people each year. The new variant of CJD differs from the classic CJD in that symptoms are more likely to be psychiatric in nature, with the usual neurological symptoms not showing up until later in the illness. Additionally, vCJD often strikes younger people, with the average victim being only 28 years old. The new variant was first described in 1996 and has been found in Great Britain and several other European countries. Worldwide, the total number of vCJD cases is 125, with most of the cases in Britain. BSE has not been detected in the US, but officials are prudently watching for any link between Chronic Wasting Disease and vCJD. Unfortunately there is no treatment available for vCJD, and the disease is always fatal.

In addition to chronic wasting disease, which occurs in deer and elk, other TSEs found in animals include scrapie, which affects sheep and goats, and transmissible mink encephalopathy. In a few rare cases, TSEs have occurred in other mammals such as zoo animals. These cases are probably caused by contaminated feed.

Wisconsin Deaths Could Play a Crucial Role
The state of Wisconsin and the Centers for Disease Control and Prevention (CDC) worry that the same link that led from BSE to vCJD might lead from Chronic Wasting Disease to vCJD. Human TSEs can occur three ways: sporadically; as hereditary diseases; or through transmission from infected individuals. Sporadic TSEs may develop because some of a person's normal prions spontaneously change into the infectious form of the protein and then alter the prions in other cells in a chain reaction. Inherited cases arise from a change, or mutation, in the prion protein gene that causes the prions to be shaped in an abnormal way.

Transmission of TSEs from infected individuals is relatively rare. TSEs cannot be transmitted through the air or through touching or most other forms of casual contact. However, they may be transmitted through contact with infected tissue, body fluids, or contaminated medical instruments. Normal sterilization procedures such as boiling or irradiating materials do not prevent transmission of TSEs. The CDC is currently conducting tests on the tissues of three Wisconsin hunters who died from TSEs. It would be exceedingly unusual – if not statistically impossible – for cases to occur in three people who hunted in the same area and all attended local wild game dinners.

TSE symptoms vary, but they commonly include personality changes, psychiatric problems such as depression, lack of coordination, and/or an unsteady gait. Patients also may experience involuntary jerking movements called myoclonus, unusual sensations, insomnia, confusion, or memory problems. In the later stages of the disease, patients have severe mental impairment and lose the ability to move or speak.

There is currently no treatment that can halt progression of any of the TSEs. The diseases tend to progress rapidly and usually culminate in death over the course of a few months to a few years. Treatment is aimed at alleviating symptoms and making the patient as comfortable as possible. A clinical trial of a potential therapy for CJD is expected to begin soon at the University of California at San Francisco.

Despite the frightening symptoms that accompany vCJD and the widespread media coverage of Chronic Wasting Disease in Wisconsin’s deer population, it is important to remember that vCJD is very rare, and that as yet there has been no causal link established between Chronic Wasting Disease and human diseases such as vCJD. Nevertheless, the Wisconsin DNR continues to keep a vigilant watch on the state’s deer herds. Wisconsin health authorities continue to warn hunters not to eat the brain, eyeballs, spinal cord, spleen, or lymph nodes of the deer they shoot or any part of a deer that appears ill. The CDC is closely following all the details of Creutzfeld-Jakob Disease and its new variant. The US Food and Drug Administration is effectively protecting the food supply from contamination, and the National Institutes of Health are researching new ways to treat and diagnose vCJD.

In addition to the ongoing research at the CDC, the National Institute of Neurological Disorders and Stroke conducts and supports research on TSEs. This research is aimed at determining how abnormal prion proteins lead to disease, at finding better tests for diagnosing CJD and other disorders, and ultimately at finding ways to treat the TSEs.

This article includes information from the National Institute of Neurological Disorders and Stroke, the US Centers for Disease Control and Prevention (CDC), the Wisconsin Department of Natural Resources and the Milwaukee Journal-Sentinel.

Each year, Medical College of Wisconsin physicians care for more than 180,000 patients, representing nearly 500,000 patient visits. Medical College physicians practice at Children's Hospital of Wisconsin, Froedtert Memorial Lutheran Hospital, the Milwaukee VA Medical Center, and many other hospitals and clinics in Milwaukee and southeastern Wisconsin.