• Posted July 14, 2023

Ticks May Be Spreading 'Wasting Disease' Among Wisconsin Deer

Ticks may be responsible for the spread of chronic wasting disease (CWD) in Wisconsin's deer population, according to a new study.

Researchers at the University of Wisconsin-Madison have found that ticks can harbor transmissible amounts of the protein particle that causes CWD, a fatal neurological disease seen in deer, elk and moose.

The pathogen, prion, can pass through soil or through bodily fluids, including feces. Prion can prompt certain proteins to fold abnormally, particularly in the brain. That can prevent these proteins from carrying out their normal functions.

Over time, the CWD prion can cause severe brain damage and eventually death in deer, the study explained.

While a lot of CWD studies focus on the role of soil in the disease's spread, researcher Heather Inzalaco was curious about other means of transmission. She's a researcher in the Wisconsin Cooperative Wildlife Research Unit, housed in the UW--Madison department of forest and wildlife ecology.

“Deer live these secret lives; we don't see everything that they do,” Inzalaco said in a university news release.

Inzalaco wondered if one possibility might be ticks. The arachnids acquire blood from CWD-infected deer, but she wondered if they could also host the prions.

“Deer will groom one another to get places that they can't reach on their own through self-grooming,” Inzalaco said. “If they're grooming each other and they're doing that to remove ectoparasites [such as ticks], that might be problematic because they're probably eating the ectoparasites.”

Inzalaco determined in the lab that ticks could carry the prions in their blood meal and that they could carry enough of the agent to infect another animal with CWD.

Then she partnered with the state Department of Natural Resources to study ticks collected from deer that hunters harvested and submitted for CWD testing. Among 176 deer with ticks studied, 15 tested positive for CWD.

Inzalaco determined that wild ticks also carried transmissible levels of prions, making them potential mechanical vectors for the disease.

“They're just like a little CWD 'tic-tac' that are possibly being eaten by the deer,” Inzalaco said.

The study did not go on further to test whether prion-carrying ticks did cause transmission to other deer.

Understanding the spread can help improve management of the disease. It isn't practical to treat all wild deer with tick preventatives, but Inzalaco believes better land stewardship could help manage tick populations.

This might include having contiguous habitat of native plant communities and properly managing areas to continue a natural fire regimen. This has been shown to limit tick populations, she said. When ecosystems have a lot of invasive plants, ticks proliferate.

The study findings were published online recently in the journal Nature.

More information

The U.S. Centers for Disease Control and Prevention has more on chronic wasting disease.

SOURCE: University of Wisconsin-Madison, news release, July 7, 2023