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Ticks Harbor and Excrete Chronic Wasting Disease Prions by Heather Inzalaco

Heather Inzalaco, Best Student Poster, The Wildlife Society (2023). Chronic wasting disease (CWD) was discovered in Wisconsin white-tailed deer harvested in fall 2001 and CWD prevalence has increased in all sex and age classes and increased in spatial extent ever since.

Heather is interested in wildlife conservation and disease ecology as it pertains to the surveillance and management of infectious diseases with zoonotic potential. More specifically, she is keen on how behavior, land-use change, and environmental and climate variables influence the interactions between hosts and pathogens and drive disease transmission. She is studying how host behaviors influence environmental contamination and indirect transmission events of chronic wasting disease. She combines camera trap data for behavioral analysis and field sampling with biochemical and molecular biology techniques to evaluate the relative magnitude of chronic wasting disease prions in mechanical vectors and environmental reservoirs for indirect transmission.

To figure out if ticks might be playing an ecologically relevant role in the spread of CWD I did two things. The first thing I did was set up artificial membrane feeding experiments with black-legged ticks (Ixodes scapularis) so that I could feed them blood inoculated with CWD prions under controlled experimental conditions. This way, I was able to control the relative amount of prions in the blood the ticks were feeding on. These feeding experiments showed that black-legged ticks could take up prions from the blood meal and excrete them. The second thing I did was collect and test ticks from actual deer. To do this I got access to the Wisconsin Department of Natural Resource’s CWD processing facility, where hunter-harvested deer heads are analyzed. I set up a table there where I examined thousands of deer heads, removing and cataloging any that were attached. After looking through almost more than 2,000 deer heads, I collected ticks from 175 of them—all of which had some blood meal in them. Lymph node testing showed 15 of the deer heads were CWD-positive. So I studied the ticks on those 15 deer and found that three had CWD-positive ticks as well. These three tick samples had transmission relevant amounts of CWD prions found in them.

I presented my initial findings at The Wildlife Society’s 2023 Annual Conference in Spokane, which earned me the Best Student Presentation Award. My poster was titled “Ticks Harbor and Excrete Chronic Wasting Disease Prions.”

Now that we know ticks can harbor CWD prions at levels potentially relevant for transmission and white-tailed deer exhibit grooming behaviors, the next step is looking at whether consuming the infected ticks can cause disease and if consumption of ticks is occurring frequently among white-tailed deer. Since we don’t know how frequently grooming events happen it is an area for future research for how understanding how frequently deer are eating ticks and if there is a risk there.


chronic wasting disease poster white-tailed deer with graphs and chats
This project all started when I began thinking about deer behaviors that may have been overlooked when we think of how chronic wasting disease might be spreading geographically. Something that’s overlooked in the literature on CWD is deer grooming behaviors. White-tailed deer (Odocoileus virginianus) practice grooming. This is when they remove ectoparasites off one another with their mouths. That could mean they are eating tick blood meals that are infected with CWD prions .