Study: 50% of deer ticks tested carry Lyme disease bacteria
May 20, 2026
Contact:
Jeff Starck
Marshfield Clinic
715-389-4978 / jeffrey.Starck@sanfordhealth.org
MARSHFIELD, Wis. – More than half of deer ticks tested by Marshfield Clinic Research Institute from its citizen science tick study were found to carry the bacteria that causes Lyme disease.
The Marshfield Clinic Research Institute launched the Tick Inventory via Citizen Science (TICS) in the spring of 2024 to investigate tick species ranges in the upper Midwest, as well as the pathogens carried by I. scapularis, also known as the deer tick or black-legged tick.
Deer ticks, which may only be the size of a poppy seed, are commonly found in Wisconsin in wooded areas and grasslands. They make contact as people brush past, latch onto their host and engorge in blood. The ticks can potentially carry pathogens that can lead to different diseases.
Reported Lyme disease cases have quadrupled over the past 20 years, according to the Wisconsin Department of Health Services. The TICS study shows the vital importance for Wisconsin residents and visitors’ awareness of ticks and knowing the signs and symptoms of Lyme disease.
“Ticks may be small, but the illnesses they carry are not,” said Jennifer Meece, PhD, Marshfield Clinic Research Institute senior vice president of research. “Knowing the symptoms of tickborne illnesses can mean the difference between early treatment and long‑term health complications.”
Meece and Alexandra Linz, PhD., a staff scientist at Marshfield Clinic Research Institute, published a pre-print paper May 15 that outlines the TICS study’s early findings. A preprint is an early posting of a research article before peer review by independent scientists or accepted at a journal.
New tick species are becoming more prevalent or detected for the first time as climate conditions shift. In the upper Midwest, Lyme disease is the most common tickborne disease, by far. The deer tick, which carries Lyme disease, can also transmit the pathogens causing anaplasmosis, babesiosis, ehrlichiosis, and several more tickborne diseases in this region.
“Having a clear understanding of tick species’ endemic ranges is critical,” Linz said. “Knowing where and how these ranges are changing, including each species’ local pathogen prevalences, will be crucial to a public health response to tickborne diseases.”
Background
In TICS first two years, citizens submitted 12,493 ticks. The most common tick species submitted was D. variabilis (American dog tick or wood tick), followed by I. scapularis. Combined, these two species comprised 99.7% of all submissions. Wood ticks are larger than deer ticks and, in our region, essentially never transmit infection to humans. Researchers received more wood ticks from citizen science submissions than from traditional tick collection methods, which suggests that people miss smaller ticks.
The paper outlines the results of species distributions from 2024 and 2025 of the TICS study along with the pathogen testing results from 707 non-engorged adult female deer ticks submitted in 2024. The positive rates were:
- 51% positive for Borrelia burgdorferi (Lyme disease)
- 9% positive for Babesia microti (Babesiosis)
- 9% positive for Anaplasma phagocytophilum (Anaplasma)
- 3% positive for Ehrlichia muris eauclairensis (Ehrlichiosis)
- Multiple pathogens were identified in 14% of tested specimens, and significant associations were observed between burgdorferi and B. microti, and B. burgdorferi and E. muris eauclairensis.
The large sample size provided by the participation of citizen scientists allowed researchers to detect rare species of ticks not yet established in the upper Midwest. One example is the northward range expansion of A. americanum (lone star tick). Over two years, the Research Institute received 22 specimens that were identified as lone star tick, 16 of which were from Wisconsin. Lone star ticks have a sugar molecule in their saliva that can cause an immune response to red meat called alpha-gal syndrome or “red meat allergy.”
Another aspect that makes the TICS study unique compared to previous tick studies in the state is that it looks at all of Wisconsin instead of specific, limited sampling locations.
Researchers and clinicians offer caution on their results—the study doesn’t indicate that there is a 50% chance of acquiring Lyme disease from a deer tick bite. We know from other studies that the risk is about 3% (and that risk decreases to 0.3% for people who receive doxycycline post-exposure prophylaxis). For a person to be at risk of developing Lyme disease, the deer tick must be attached for at least 36 hours.
“We don’t want to scare people off from being outdoors – Wisconsin residents and its visitors love the state because of the natural wonders and beauty,” Meece said. “We just encourage people to take proactive steps to protect themselves from ticks and be observant if they do find themselves with a tick bite.”
Impact on health care
Awareness and early recognition of symptoms are key to preventing serious disease. Wisconsin saw 6,469 cases of Lyme disease in 2024 – the highest on record – with an average of about 4,600 cases reported each year during 2019-2023, according to Wisconsin Department of Health Services. Lyme disease is the most common vector-borne disease in the U.S., with an estimated 476,000 people diagnosed and treated each year, according to the Centers for Disease Control and Prevention.
If you find a tick attached to your skin, use tweezers to remove the tick as soon as possible. Grasp the tick close to the skin’s surface to avoid squeezing the tick’s body. Pull the tick away from the skin with steady pressure to avoid causing the tick mouthparts to break off and remain in the skin.
Symptoms of illnesses resulting from a tick bite can include rash, fever, joint pain, and fatigue within several days to weeks. Contact your medical provider if you have these symptoms. Lyme disease doesn’t always result in the classic bullseye rash. Bring the tick in a small plastic bag to your provider, if possible.
“Testing is important, because early treatment is highly effective in preventing later stages of the disease from developing,” said Dr. Thomas Boyce, a pediatric infectious disease physician with Marshfield Clinic. “If you remove a deer tick that is attached and engorged, a single dose of an antibiotic (doxycycline) can reduce the risk of contracting Lyme disease ten-fold.”
TICS study researchers say their efforts, and those by public health departments, highlight the need for increased awareness of tick bite prevention strategies in the public.
To reduce the risk of tick bites, spray the insecticide permethrin on clothing, sleeping bags, and tent fabric. Wear clothing that covers your skin. Finally, have someone help you check for ticks after time spent outdoors.
Get your tick kit
For more information, or to request a pre-paid collection kit be sent to you, contact tics@marshfieldclinic.org or 1-715-389-7796 (extension 16462). Parks and nature centers interested in having kits available for their visitors also are encouraged to contact Marshfield Clinic Research Institute.
Once the tick, dead or alive, has been placed in the collection kit, just drop it in the mail to submit. Any tick found on people or pets is appreciated. Each kit will come with a unique identification number that people can use to look up, via an online dashboard, the species of ticks they submitted.
What’s next?
The TICS study, which had a humble original goal of 500 ticks, has already launched several other projects.
- TICS has expanded into Bemidji in northern Minnesota.
- Researchers are performing Microbiome analysis by sequencing 200 burgdorferi positive and 200 B. burgdorferi negative ticks to learn more about non-pathogenic microbes that may influence whether or not a tick carries a pathogen.
- They are partnering with Bayfield County Public Health and University of Minnesota to investigate Powassan virus.
- Researchers are working with University of Wisconsin to determine where and when most people are at risk of tickborne disease exposure as well as writing a methods paper about how to conduct citizen science.
- The Research Institute also engaged individuals who have experienced Lyme or another tick-infection to tell their story.
About Sanford Health
Sanford Health, the largest rural health system in the United States, is dedicated to transforming the health care experience and providing access to world-class health care in America’s heartland. Headquartered in Sioux Falls, South Dakota, the organization has 55,000 employees and serves more than 2 million patients and nearly 415,000 health plan members across the upper Midwest including South Dakota, North Dakota, Minnesota, Wyoming, Iowa, Wisconsin and the Upper Peninsula of Michigan. The integrated nonprofit health system includes a network of 58 hospitals, 289 clinic locations, 145 senior care communities, 4,500 physicians and advanced practice providers and 1,100 active clinical trials and studies. The organization’s transformational virtual care initiative brings patients closer to care with access to nearly 80 specialties. More than 400 residents and fellows are trained each year through graduate medical education with Sanford Health fully funding and supporting 29 of the 40 available programs. Sanford Health also includes Lewis Drug, a pharmacy and retail chain with 60 locations in three states and nearly 190 pharmacists. Learn more about Sanford Health’s commitment to shaping the future of rural health care across the lifespan at sanfordhealth.org or Sanford Health News.
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