The data reflecting the current spike in tick-borne illness is significant. In Wisconsin, the state Department of Health Services reported a rate of 44 tick-bite visits for every 10,000 emergency room visits for the week ending April 19. According to public health entomologist Xia Lee, this represents roughly double the number of ER visits seen at the same time last year.
While the spike is evident in the Midwest, the trend is not isolated. Data from the NBC Boston report indicates that ER visits for tick bites across the Northeast have climbed to their highest levels for this season in nearly a decade. This suggests that tick populations are becoming a more frequent point of concern for residents during the early spring months.
Climate anomalies and the ‘frost-free’ window
From a public health perspective, the timing of tick emergence is closely tied to temperature thresholds. Ticks are hardy, but their activity is governed by the presence of frost and humidity. Andrew Lewandowski, a pediatrician and board member for Healthy Climate Wisconsin, notes that climate change is increasing the number of frost-free days, which allows ticks to emerge from dormancy earlier and increases their biting behavior.
The recent weather patterns provide a clear catalyst for this year’s numbers. Despite a winter that felt more typical than in recent years, February was almost 6 degrees warmer than usual in Wisconsin, and the state is currently experiencing its wettest April on record. These conditions—warmth combined with high humidity—create an ideal environment for tick survival and movement.
“With some of these warm snaps that we get in the winter time, it’s increasing the timeframe that ticks can be active and can spread disease,” Andrew Lewandowski, pediatrician and board member for Healthy Climate Wisconsin
This environmental shift is particularly evident in the behavior of wood ticks, which are appearing about two weeks earlier than normal. When these early wood ticks are combined with the deer tick populations already present in the environment, the result is a concentrated spike in emergency department visits. This shift in timing often catches the public off guard, as many assume a snowy winter automatically equates to a slower tick season.
Differentiating the risks of wood and deer ticks
It is critical for patients and providers to distinguish between the types of ticks encountered, as the disease risks differ. Wood ticks are often the first to appear during these early warm snaps, but deer ticks (also known as blacklegged ticks) are the primary vectors for Lyme disease.
For more on this story, see Tick bite ER visits hit highest weekly rate since 2017.
The geographic reach of the deer tick has expanded. PJ Liesch, an extension entomologist at UW-Madison, reports that they have spread from the woods of northwestern Wisconsin to nearly all corners of the state. The risk of infection upon a bite is significant; Liesch notes that an average of 20 percent of juvenile deer ticks and 40 percent of adult deer ticks are positive for Lyme disease.
Because of these factors, medical professionals are preparing for a surge in diagnoses. Dr. Greg Demuri, a professor of pediatric infectious diseases at the University of Wisconsin School of Medicine and Public Health, has expressed his expectations for the coming months.
“I think it’s going to be a big year for Lyme,” Dr. Greg Demuri, University of Wisconsin School of Medicine and Public Health
The danger is highest during the spring, when people return to outdoor activities and tick populations are highly active. While officials will not know the full extent of the Lyme disease impact until the season typically peaks around June, the early ER data serves as a leading indicator of the risk.
Clinical presentation and early intervention
For those seeking care in the emergency department, the challenge is that early tick-borne illnesses often mimic other common ailments. Dr. Peter Adler, emergency department chief at UPMC Passavant, explains that the initial symptoms are often indistinguishable from the flu, including fever, chills, nausea, and generalized body aches.
The most definitive early warning sign is the characteristic bull’s-eye-shaped rash. This rash typically forms at the site of the bite about one to two weeks after the tick has attached and the bacteria have entered the system. Early detection is the primary goal to ensure that the infection is managed promptly and to prevent the progression of the illness.
Treatment typically involves the administration of appropriate antimicrobial medications. Medical professionals may assess the duration of the tick’s attachment and other risk factors to determine the most effective course of pharmaceutical intervention to stop symptoms from developing or worsening.
This follows our earlier report, ECDC Report: Monitoring SARS-CoV-2, MERS, and Global Health Threats.
Public health officials emphasize that prevention remains the most effective tool. This includes wearing long clothing, avoiding tall or brushy grass, and using insect repellent containing DEET. Julie McCarthy, the assistant public health director for nursing and behavioral health in Needham, Massachusetts, points out a common misconception: many people associate DEET only with mosquitoes, but it is a critical component of tick prevention.
The role of pets and reporting trends
Human risk is not only tied to where people walk, but also to the animals they bring into their homes. Dog owners often serve as an unintentional bridge for ticks to enter living spaces. In Jamaica Plain, dog owner Sharon Woo shared that she has noticed more ticks on her dogs this year, leading her to vaccinate her pets against Lyme disease.
“First thing when tick season starts, I’m more worried about my dogs,” Sharon Woo, dog owner
The concern is practical: dogs carry ticks from the outdoors into the home, where the ticks can then transfer to their owners. This intersection of pet ownership and human risk adds another layer to the public health challenge, as ticks are not limited to wooded trails and can be found in well-manicured backyards.
Looking at the broader timeline, the increase in reported cases is part of a longer trend. Wisconsin saw a record 6,469 cases of Lyme disease in 2024, with cases quadrupling over the last 20 years. However, this rise is not solely due to more ticks. Julie McCarthy notes that the data has been slowly creeping up
due to a combination of expanded geographic spread, better reporting processes, and an increased desire among patients for testing.
As climate patterns continue to shift, the timeframe for tick activity is likely to expand. Without efforts to mitigate these environmental changes, the window for infection will remain open longer each year, placing a sustained burden on emergency departments and primary care providers across the Northeast and Midwest.
