Why Lyme disease isn’t the only tick-borne infection you need to worry about
Co-infections are a real danger as more ticks carry multiple pathogens, study suggests.
When you show up at your family doctor’s office with a tick bite, chances are the first thing your physician might think about is Lyme disease, but new research suggests you both might need to worry about multiple infections, not just one.
A study published in the December 2025 edition of Ecosphere details a worrisome trend in the northeastern United States – one that could have implications for Canada as well, due to exploding tick populations and rising case counts of tick-borne illnesses in several regions of the country.
The researchers analyzed more than 2,000 black-legged ticks – one species that carries Lyme disease – collected in their nymph stage over nine years in Dutchess County, which is about 140 kilometres north of New York City on the border with Connecticut. The study found a significant percentage of the nymphs carried more than one pathogen that could cause infection in humans – meaning many patients could be showing up in doctors offices with not only one tick-borne disease, but several.
“More than a third (38.8%) of nymphs were infected with at least one pathogen, and Borrelia burgdorferi (the agent of Lyme disease) was detected in all six sampling locations and years,” the article says.
“Pathogens included Babesia microti (NIP = 21.4%), (Borrelia) burgdorferi (19.3%), Anaplasma phagocytophilum (5.8%), (Borrelia) miyamotoi (1.5%), Powassan virus (<0.01%), and two regionally emergent Rickettsia (10 nymphs sampled in 2016 and 2021).”
Babesiosis on the rise
The researchers highlight a concerning increase in one particular pathogen: Babesia microti – the organism that causes babesiosis – at more than 20 per cent.
“Rates of (Babesia) microti infection were high relative to prior work, and coinfection with (Borrelia) burgdorferi increased during the study period,” the researchers write.
Babesiosis can cause flu-like symptoms, extreme fatigue and weakness, nausea and anemia. Otherwise healthy patients recover with minimal medical attention but the infection can be severe and even deadly in the elderly or people with compromised immune systems.
This isn’t the first paper to warn health-care professionals about severe and potentially deadly tick-borne co-infections. In a case study published last year, physicians at Brantford General Hospital in Southwestern Ontario sounded the alarm about what they believe is the region’s first reported case of anaplasmosis, which can be fatal in one to seven per cent of cases. Other serious tick-borne infections seen recently in Canada are Powassan virus – which can lead to neurological damage in 50 per cent of severe cases and has a fatality rate of 10 per cent – and Rocky Mountain spotted fever.
Still, many primary-care physicians in Canada are unfamiliar with tick-borne illnesses and struggle to diagnose and treat them. Current testing methods for Lyme disease, the country’s most common vector-borne infection, are prone to false negatives.
Testing for other tick-borne pathogens is also a challenge. Hard tick-borne relapsing fever, caused by Borrelia miyamotoi, has been detected in Canada and produces symptoms very similar to Lyme disease, but there is no standard test for it in this country. That raises a troubling question: how many Canadian patients infected with Borrelia miyamotoi have gone undiagnosed because of a false negative test for Lyme disease?
The study’s results have clear implications for primary care physicians, says Dr. Melvin Sanicas in the April edition of his Science Speaks blog, published by IDSA.
“Suspected tick-borne illness shouldn’t automatically be assumed to be Lyme disease or any other single tick-borne infection alone,” says Sanicas, a prominent physician-scientist specializing in global health, immunology, and preventive medicine.
“Considering the possibility of co-infection can lead to more accurate diagnoses and better treatment decisions. As tick populations expand and the range of pathogens they carry grows, clinician awareness and prevention will become even more important.”