Researchers tested 2,000+ blacklegged ticks in New York over 9 years
• 38% of ticks carried at least one pathogen capable of infecting humans
• About 10% carried multiple pathogens (co-infection)
• The most common combination was Lyme disease + Babesia microti
• Babesia was found in 21% of ticks, higher than previous estimates
• Bartonella was not detected in the ticks tested at these study sites
A new study from researchers at the Cary Institute of Ecosystem Studies and SUNY Upstate Medical University highlights a growing concern in the Northeast: ticks are increasingly carrying multiple disease-causing pathogens.
Researchers tested more than 2,000 blacklegged ticks collected between 2014 and 2022 and screened them for 16 different pathogens.
The results show a significant level of infection in ticks that commonly bite humans.
• More than 38% of nymphal ticks carried at least one pathogen capable of infecting people.
• About 1 in 10 ticks carried two or more pathogens.
• The most common co-infection was Borrelia burgdorferi (Lyme disease) together with Babesia microti, the parasite that causes babesiosis.
This has important clinical implications. Different pathogens require different treatments. Lyme disease is treated with antibiotics, while babesiosis requires antiparasitic medications. If clinicians test for only one infection, co-infections may be missed.
Babesia stood out in the study. It was found in more than 21% of ticks, which is higher than earlier estimates. In the final years of the study, Babesia was even more common than Lyme bacteria in some samples.
Other pathogens detected included:
• Anaplasma phagocytophilum (anaplasmosis)
• Borrelia miyamotoi (hard tick relapsing fever)
• Rickettsia species associated with spotted fevers
• Powassan virus, a rare but serious virus that can cause brain inflammation
One notable finding: Bartonella bacteria were not detected in any of the ticks tested at the Cary Institute study sites. Researchers noted that while some clinicians suspect Bartonella may be tick-borne, this particular study did not find evidence of it in the sampled ticks.
Researchers emphasize that co-infection risk is rising, and healthcare providers in the Northeast should consider testing for multiple pathogens when patients become ill after a tick bite.
One striking statistic: the probability of exposure to a pathogen from a single nymph tick bite is approaching 40%.
For people spending time outdoors, tick prevention and routine tick checks remain critical.
LaDeau, Shannon L., KellyOggenfuss, AlexanderSchmidt, SaravananThangamani, and Richard S.Ostfeld. 2025. “Ecological Dynamics of Blacklegged Ticks, Vertebrate Hosts, and Associated Zoonotic Pathogens in Northeastern Forests.” Ecosphere16(12): e70508. https://doi.org/10.1002/ecs2.70508
Gabriella True
