Human Health and Prion Diseases

In August, 2008 the first Michigan case of Chronic Wasting Disease (CWD) was confirmed in a 3 year old deer from a privately owned animal facility in Kent County. CWD is fatal neurological disease found in cervids (deer, elk and moose). The disease is a transmissible spongiform encephalopathy (TSE), caused by an abnormal protein known as a prion.

To date, CWD is not known to cause or be associated with disease in humans. No increase in human prion disease has been observed in areas of the western United States where CWD has been endemic in cervid populations for decades. However, because much is still unknown about prion diseases, the Centers for Disease Control and Prevention and the World Health Organization advise that humans do not consume animals that have been tested and are known to be infected with CWD. In general, people should not handle or consume wild animals that appear sick or act abnormally, regardless of the cause.

CWD prions are primarily found in central nervous system tissues (e.g. brain and spinal cord) and the lymphatic system (e.g. tonsils, lymph nodes and spleen) of infected cervids. Humans should avoid the handling or consumption of these tissues. Hunters should wear disposable gloves while field dressing and bone out meat from the carcass. Recent research has shown that CWD prions may also be found in the saliva and urine of the infected animal. Experiments conducted suggest that CWD prions can persist in the environment and may indirectly infect other susceptible animals that come into contact with the contaminated environment.

There are many different forms of prion diseases that affect humans and animals. Currently, the only known animal prion disease that has caused disease in humans is Bovine Spongiform Encephalopathy (BSE), or "mad cow" disease. This disease in humans is known as variant Creutzfeldt-Jakob disease (vCJD). Since the discovery of variant CJD in 1996, 208 people in 11 countries have been diagnosed with the disease. Only 3 cases of BSE have been found to date in the cows tested in the United States; 1 cow imported from Canada in 2003, 1 cow from Texas in 2004, and 1 cow from Alabama in 2006. No cases of domestically acquired vCJD have been found in the United States.

While variant CJD may be the most well known human prion disease, it is not the most common. Sporadic CJD, a form of prion disease not associated with any animal disease, accounts for approximately 90% of all human prion disease cases and is believed to be caused by a spontaneous genetic mutation that causes the production of the abnormal prion protein that can not be broken down by the body. Nearly all of the other human prion diseases are familial prion diseases (meaning they run in a family and can be passed down from one generation to the next) caused by an inherited gene mutation. The risk of acquiring a prion disease from an animal source is extremely remote. Research suggests that the biological differences between humans and animals prevent animal prion diseases from being easily transmitted to people. Scrapie is an animal prion disease in sheep that has been recognized since the 18th century and has never been shown to be transmitted to or cause disease in humans.