Lyme disease rates have more than doubled in Wisconsin over the past several years with more than 5,000 reported cases during 2022. With little information available on disease hotspots, many residents are unsure of how to protect themselves. But over the past couple of years, John Orrock, the Wayland E. Noland Distinguished Chair in Integrative Biology, has led a research project to identify how climate affects the activity of animals that feed and infect ticks, which could aid in efforts to predict future disease hotspots to help inform residents when risks of becoming infected are high.
“I have focused a lot of my career on how the spatial pattern of animal movement affects interactions among organisms. But honestly, spatial patterns make the most sense when you include the aspect of time,” Orrock says.
The spatial pattern of animal activity is relevant to Orrock’s research because, for a disease to be transmitted, the animal and the tick must be in the same space simultaneously. For example, if an animal — say a mouse or a deer — comes out 10 minutes later due to weather conditions, it may avoid contact with the tick and therefore avoid disease. Based on this knowledge, Orrock became interested in investigating how the intersection of space and time impacts disease.
Orrock and his team started studying mice specifically because of the impact they have on the zoonotic disease cycle.
“Even if there are millions of ticks, disease transmission depends on how often ticks encounter infected animals like rodents,” Orrock says. “Timing is essential for determining whether or not organisms interact with one another, and in this case it's ticks, mice and a third party — the pathogen.”
Because Borrelia burgdorferi — the bacterial pathogen that causes Lyme disease — is not transmitted from female ticks to their offspring, young ticks must feed on an infected animal to become infected themselves. Many small ticks feed on rodents, and rodents can maintain persistent Lyme infections. As a result, the rodents may play an important role in the dynamics of Lyme disease because rodents infect ticks that later go on to bite (and possibly infect) humans.
Using a new tool that he developed to measure activity timing in wild rodents, Orrock and his team (Dr. Alli Brehm, graduate students Mark Fuka and Biz Locke, and undergraduate Amelia Weidemann), along with collaborators Professor Lynn B. Martin and Dr. Vania Assis at the University of South Florida, began their research project tracking rodents through the National Ecological Observation Network (NEON).
“By using our new method of measuring timing at sites across the U.S. to determine if there are predictable changes in rodent behavior that lead to predictable changes in rodent disease, it could lead to our ability to predict changes in large-scale human disease risk,” Orrock says.
So far, Orrock and his team have studied mice activity for two years at eight different NEON sites around the U.S. Using data on temperature and precipitation patterns and the timing of mouse behavior, they are using statistical models to explore whether it is possible to predict when rodents are active and thus whether they are likely to encounter ticks.
“I was excited to see that, by implementing this new technique for measuring timing at many sites across the U.S, we've been able to understand animal behavior at spatial scales that are unprecedented,” Orrock says. “We're showing that animal behavior can be understood at large spatial scales.”
By understanding the relationship between climate, space, and time, scientists hope to be prepared to identify where hotspots and coldspots of disease risk may form. The data collected from this research project may benefit Wisconsin specifically because the state has proved to be a hotspot for tick-borne disease. Knowing this information would better prepare citizens to avoid hotspots, reducing the risk of disease.
“These questions are particularly relevant and appropriate for places where Lyme disease is a big issue for humans, aka Wisconsin,” Orrock says.