Increase of tick-borne diseases in Illinois highlights the need to prevent tick bites year round

More than 6,400 Illinois residents were diagnosed as having a tick-borne disease from 2004 to 2022, with cases occurring in every county in the state and in every month of the year. That number represents dramatic growth in human cases of tick-borne diseases during that time and reflects the urgency of prevention efforts, according to a new study in Ticks and Tick-borne Diseases.

For the study, researchers the University of Illinois Urbana-Champaign analyzed 6,423 cases reported to the Illinois Department of Public Health and found that the annual number of reported tick-borne disease cases increased by an average of 23 each year during the study period. Lyme disease accounted for most cases, adding, on average, 18 cases per year.

The researchers also compared human disease data with canine disease data and found that exposure patterns in dogs largely mirrored those seen in people.

“My big takeaway for the public is that we see tick-borne diseases 12 months out of the year and in every county in the state of Illinois,” senior author Rebecca Smith, DVM, PhD, an epidemiologist and professor of pathobiology at the University of Illinois, said in a university news release. “We have different tick-borne diseases in different places and different risks in different places, but every county, every month, there is a risk.”

Lyme most common tick-borne disease in Illinois

Every Illinois county reported at least one tick-borne disease case during the study period. Lyme disease was the most commonly reported, with cases concentrated in northern parts of the state. Ehrlichiosis and spotted fever group rickettsioses were more common in southern Illinois, and anaplasmosis occurred most often in the north and south.

Cases were more common in rural counties, areas with higher deer-harvest rates, and counties with lower median household incomes.

The researchers also found that, while cases peaked in June and July, every tick-borne disease except babesiosis was reported in every month of the year. The surge in cases in early summer corresponded to the peak period of activity for nymphal ticks, which are smaller than adult ticks and harder to spot. 

The researchers noted that the rise in reported cases likely reflects a combination of factors, including environmental changes and increased awareness and testing.

Prevention ‘starts by preventing tick bites’

Ticks have become more widespread in recent years—not just in Illinois, but across the country. “Definitely there is a geographic expansion, and we can see the effects of [them] expanding to areas where maybe in the past ticks were limited by overwintering temperatures,” says Pilar Fernandez, PhD, assistant professor at the Allen School for Global Health at Washington State University. 

And ticks aren’t just expanding their geographic footprint. They’re moving beyond forests into new ecosystems. In endemic areas, “anywhere when you go outside, particularly when you encounter some sort of vegetation—even in your backyard—risk is not zero,” says Alvaro Toledo, PhD, associate professor in the department of entomology at Rutgers University.

Neither Fernandez nor Toledo was involved in the study.

Because there are no vaccines or other large-scale public health prevention strategies for tick-borne diseases in people, experts say proactively avoiding tick bites when outdoors, performing tick checks after spending time outdoors, and seeking prompt treatment if symptoms develop are the best ways to stay safe. 

Toledo advises wearing light-color clothing with long sleeves, long pants, and socks when outdoors in endemic areas and treating outdoor clothing and gear with an acaricide (a pesticide specifically designed to kill ticks and mites) like permethrin. (Always apply permethrin to clothes and never directly to the skin.)

Checking for ticks on people, pets

People who live in endemic areas (where ticks carry diseases such as Lyme) and whose yards adjoin grasslands or forests can make wood-chip moats to help keep ticks at bay. 

“You can create an area between the forest and your grass with wood chips, because the wood chips will be drier and ticks are very sensitive to dry conditions,” says Adela Oliva Chavez, PhD, assistant professor in the department of entomology at the University of Wisconsin-Madison who also was not involved in the Illinois study. “So if you make a perimeter around your house [with wood chips] that is wide enough for the ticks not to be able to crawl [across], that can help.”

It’s also important to perform tick checks immediately after being outside in endemic areas, say experts. Transmission risk is far less within 24 hours of a tick attaching to skin. 

If you find a tick, says Chavez, “the best way to remove it is to find tweezers, come as close as possible to what we would consider the head of the tick and [pull in] a straight-up movement so that the tick comes out.” Try to remove all parts of the tick, especially the mouthparts, continues Chavez, because they contain salivary glands which, if embedded in skin, increase the risk of transmission and secondary infection. 

Cat and dog owners should perform tick checks on their pets regularly, adds Chavez. “Owning a pet increases your chances of a tick bite, because they might bring the tick inside your house,” she says.

Do not use petroleum jelly or try to burn the tick to remove it, she continues. Those methods may trigger the tick to release infected fluid into the skin. 

For more information on removing ticks, she recommends consulting the Centers for Disease Control and Prevention’s pictorial instructions. 

“Prevention of tick-borne diseases starts by preventing tick bites,” concludes Toledo. “That's the critical step that people can proactively do to prevent Lyme disease, Rocky Mountain spotted fever, and so on.”