A type of Lyme disease caused by a rare type of bacteria that leads to more severe symptoms has appeared in a new 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.
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.
NYDOH lab members collected 147 nymph deer ticks – ticks in the second stage of life – along hiking trails in the wooded area of the patient’s home and 22 from a nearby forest.
One tick from the patient’s yard tested positive for Borrelia mayonii. In October, investigators collected 305 adults ticks from the same two locations, of which nine from the patient’s property tested positive for the bacterium.
Based on the findings, the CDC report stated the investigation indicated local tick-borne transmission of Borrelia mayonii.
The higher prevalence of the bacterium in adult ticks suggests there is the presence of a local ‘reservoir’ for the ticks, an animal that harbors and perpetuates a disease.
The evidence also suggests ‘established enzootic transmission,’ low-level spread and maintenance of a pathogen, in the local surrounding New York area, as opposed to accidental introduction of the bacterium from a place where it is endemic, such as the Midwest.
Doctors have warned recently that this tick season could be a particularly one and hospital visits for tick bites are already up.
Emergency Department tick-bite visits have reached their highest level nationwide in nearly a decade, with 71 visits per 100,000 people — more than double the average of about 30 per 100,000 for this time of year.
Ticks reside in grassy, brushy and wooded environments and the season typically begins in May.
New data updated April 12 show the Northeast now has the highest rate per population – at 163 tick-related ED visits per 100,000 people, up from just 52 in March.
That already outpaces recent full-year highs in the region, which ranged from 74 to 89 per 100,000 between 2021 and 2025.
Ticks reside in grassy, brushy and wooded environments and the season typically begins in May.
The arachnids spread disease by biting into the skin and feeding on blood.
To prevent infections, people should cover their skin when outdoors with long pants or sleeves, use tick repellent, always check themselves for ticks after being outside and see a doctor right away if they do find a tick attached to their body.
