By ALEXA LARDIERI, US HEALTH EDITOR
A type of Lyme disease caused by a rare bacterium that leads to more severe symptoms has appeared in a US state for the first time, health officials are warning.
A resident of Herkimer County, New York, located in the central part of the state, tested positive for Borrelia mayonii last year, according to a new CDC Morbidity and Mortality Weekly Report.
Prior to this case, the pathogen had only ever been detected in people in Minnesota and Wisconsin.
Lyme disease is a tick-borne illness typically caused by the bacterium Borrelia burgdorferi transmitted to humans from the bite of an infected blacklegged tick, also known as the deer tick.
Borrelia mayonii is also transmitted by the deer tick, but in far rarer cases.
Both bacteria cause similar symptoms, including fever, chills, headache, muscle and joint pain, rash and late-stage arthritis.
Borrelia burgdorferi causes the hallmark ‘bullseye’ rash, while Borrelia mayonii causes a widespread rash, higher fevers, nausea, vomiting and a higher amount of bacteria in the blood.
On July 8, 2025, New York State Department of Health was notified that the resident tested positive for the rare bacterium after they had received treatment for symptoms ‘consistent with tick-borne infection’ the previous month.
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Lyme disease is a tick-borne illness typically caused by the bacterium Borrelia burgdorferi transmitted by a deer tick. Borrelia mayonii is also transmitted by the deer tick, but in far rarer cases
The above shows Borrelia mayonii surveillance and detections by county in New York state from 2021 to 2025
Testing also revealed the patient was co-infected with anaplasma phagocytophilum, a separate deer tick-transmitted bacterium that causes human granulocytic anaplasmosis (HGA).
HGA commonly causes a benign fever and infections typically resolve on their own. However, life-threatening complications can occur and about three percent of patients die, according to a report from the NIH.
The CDC has reported approximately 52,000 cases of HGA between 2000 and 2021. It is the second-most commonly reported tick-borne disease in the US after Lyme disease.
Approximately 89,000 cases of Lyme disease were reported to the CDC by state health departments in 2023.
However, more recent estimates using other surveillance and reporting methods suggest that as many as 476,000 people are diagnosed with and treated for the disease each year in the US.
Meanwhile, there have been fewer than 20 human cases reported of Borrelia mayonii and all of them had been in the upper Midwest prior to the New York patient.
The New York patient was treated with the antibiotic doxycycline and made a full recovery.
Because the patient had spent time outdoors and reported no recent travel, a public health investigation was ordered to investigate the source of the person’s Borrelia mayonii infection, the CDC report stated.