Rare Lyme disease-causing strain spreads to new state: What to know

(NEXSTAR) – A rare pathogen known to cause Lyme disease has been detected in a new state, far from where it has traditionally been found.

Lyme disease, spread by ticks, isn’t rare. In 2023 alone, more than 89,000 cases of the disease were reported to the CDC. The actual number of people diagnosed each year could be closer to 476,000, health officials say.

While nearly every state had a reported case of Lyme disease in 2023, a map from the CDC, seen below, shows that the majority came from Wisconsin, Minnesota, and throughout the Northeast.

The disease is spread by the blacklegged tick, sometimes known as the deer tick or by its scientific name, Ixodes scapularis. Symptoms of Lyme disease can include a “bullseye” rash and a fever to complications with your nervous system, heart, and joints, according to the Cleveland Clinic.

The tick-borne illness is typically caused by the bacterium Borrelia burgdorferi, the CDC explains. However, in rare cases, the bacterium Borrelia mayonii may also be to blame.

B. mayonii is considered “a rare, newly emerging species,” Wisconsin health officials say. It was found to have caused human illness for the first time in a Minnesota resident, according to the state’s Department of Health. Three years later, B. mayonii was identified as a cause of Lyme disease.

Between 2013 and 2024, Wisconsin reported 10 cases of Lyme disease related to B. mayonii. The symptoms of Lyme disease caused by B. mayonii are similar to cases caused by B. burgdorferi: fever, chills, headache, rash, and muscle or joint pain, with arthritis also reported in later-stage infections.

Wisconsin and Minnesota have, over the last decade, remained the only states where B. mayonii has been detected. That appears to have changed in 2025, a new report from the CDC shows.

Last July, a resident in Herkimer County, New York, tested positive for B. mayonii, the report, released earlier this month, explained. A nymph Ixodes scapularis – aka, a young blacklegged tick – collected from the resident’s property tested positive for B. mayonii. So, too, did nine more ticks.

This is the first time the “emerging species” has been found in New York, according to the report.

While concerning, few of the ticks tested by the New York State Department of Health tested positive for B. mayonii. The CDC reports that one nymph out of 627 and nine adults out of 891 tested positive, or 0.2% and 1%, respectively. On the patient’s property, 0.7% of the nymphs and 3.9% of the adults tested positive for B. mayonii.

The authors of the CDC report said continued surveillance of tick-borne disease is “critical.”

The blacklegged tick has been found across more than half the U.S., CDC data shows. A map from the agency shows it has been found from North Dakota south to Texas, east to Florida, and back north to Maine.

In addition to Lyme disease and anaplasmosis (which the New York patient also tested positive for), the blacklegged tick can spread babesiosis, hard tick relapsing fever, ehrlichiosis, and Powassan virus.