ELi on EARTH: Chronic Wasting Disease in Local Deer

Photo: White-tailed deer, credit Scott Bauer, USDA Agricultural Research Service

Deer are becoming increasingly prevalent in and around East Lansing, and this is leading to a number of health and safety concerns. Besides the potential problem of collisions between deer and humans, there are also tick-borne diseases like Lyme disease that travel via deer, as previously reported for ELi. Now scientists are currently trying to figure out whether another disease showing up in our local deer—chronic wasting disease—could be transmissible to humans.

Chronic wasting disease (CWD) in deer is a form of transmissible spongiform encephalopathy (TSE), the class of diseases that also cause “mad cow disease” (bovine spongiform encephalopathy), a fatal disease which has been transmitted to humans. While some scientific investigations have suggested that CWD is unlikely to be transmissible to humans, a paper published this month in the Journal of Virology indicates that “the barrier preventing transmission of CWD to humans may be less robust than estimated” previously.

Regular readers of ELi’s Council Capsule will recall that on August 18 of this year, East Lansing’s Environmental Services Administrator Cathy DeShambo told City Council that three deer in Meridian Township have been identified as having CWD. Indeed, the Michigan Department of National Resources (DNR) announced in May that the “state’s first [identified] case of chronic wasting disease in free-ranging white-tailed deer” occurred in Meridian Township.

According to that announcement, “The animal was observed last month wandering around a Meridian Township residence and showing signs of illness. The homeowner contacted the Meridian Township Police Department, who then sent an officer to euthanize the animal. The deer was collected by a DNR wildlife biologist and delivered for initial testing to the DNR Wildlife Disease Laboratory” at MSU. The U.S. Department of Agriculture’s National Veterinary Services Laboratory in Iowa confirmed the finding.

Based on DeShambo’s report to Council, three local cases have now been confirmed. This is one reason why local governmental agencies are considering “culls,” i.e., controlled kills of local deer.

CWD is caused by prions, a biological phenomenon posited and named by Stanley Prusiner, M.D., who received the Nobel Prize in 1997 for his work on prions. Most transmissible diseases are caused by pathogens that contain genetic material; examples of these pathogens are viruses and bacteria. But prions are infectious proteins that replicate themselves. (“Prion” is short for “proteinaceous infectious particle.”) When they infect the nervous system of an organism like a human or deer, the proteins replicate themselves, changing the structure of the brain and other neural tissues. Human prion diseases include kuru and Creutzfeldt-Jakob Disease.

Prion diseases are not treatable and are believed to always be fatal. They are so strange—caused by proteins self-replicating without DNA—that for many years, Prusiner was mocked by other scientists for putting forward the very concept.

Mad cow disease and kuru are transmitted to humans when humans eat the prion-laden parts of infected animals, including brains. There is no evidence of any transmission of CWD from deer to humans, but people are being warned not to eat any animals that appear to be sick and not to salvage road-killed deer. They are asked instead to contact the Michigan DNR so that that agency’s staff can retrieve such animals for testing.

According to the DNR, CWD is transmitted from deer to deer via “saliva and other body fluids of infected animals. Susceptible animals can acquire CWD by direct exposure to these fluids or from environments contaminated with these fluids or the carcass of a diseased animal. Once contaminated, research shows that soil can remain a source of infection for long periods of time, making CWD a particularly difficult disease to eradicate.”

The DNR wants members of the public, including hunters, to report deer that appear to be unusual thin or exhibiting unusual behavior (“for example, acting tame around humans and allowing someone to approach”). Suspicious animals should be reported by calling 517-336-5030. Road-killed deer should be reported by calling 517-614-9602 and leaving “a voicemail with location information and staff will attempt to pick up carcasses on the next open business day.”