Tickborne diseases are the most common vector-borne infections in the U.S., and for decades Lyme disease has dominated the conversation in endemic regions. But ticks are carrying more than Lyme alone and co-infections are becoming harder to ignore. New research suggests ticks are harboring a wider mix of pathogens than previously recognized, and that co-infections are becoming an increasingly important part of the clinical picture.
A recent study published in Ecosphere offers a closer look at this shift in the northeastern U.S. Researchers analyzed more than 2,000 nymph-stage blacklegged ticks (Ixodes scapularis) collected over nearly a decade in Dutchess County, New York, and found that many carried pathogens capable of infecting humans, sometimes more than one at a time.
About 10 percent of the ticks studied were infected with at least two pathogens. The most common pairing was Borrelia burgdorferi, the bacterium that causes Lyme disease, and Babesia microti, the parasite responsible for babesiosis. For clinicians, that overlap is more than an academic concern. Lyme disease is typically treated with antibiotics such as doxycycline, while babesiosis requires antiparasitic therapy, most often a combination of atovaquone and azithromycin. When a single tick bite transmits both infections, recognizing and treating each becomes essential.
Co-infections can also complicate diagnosis. Symptoms often overlap, and illness may be more severe or prolonged than in single-pathogen infections. Together, these findings reinforce a growing reality: In endemic areas, suspected tickborne illness cannot be assumed to be Lyme disease alone.
Multiple pathogens, one vector
The Ecosphere study also highlights just how diverse tickborne pathogens can be. More than one-third of the ticks tested were infected with at least one pathogen known to cause human disease. In addition to Borrelia burgdorferi and Babesia microti, researchers identified Anaplasma phagocytophilum and Borrelia miyamotoi. Less commonly, ticks carried Rickettsia species, and one tick tested positive for Powassan virus, a rare but potentially serious infection.
One of the more striking findings was the increasing detection of Babesia microti. Toward the end of the study period, it appeared frequently, sometimes even more often than Borrelia burgdorferi in sampled ticks. That trend suggests babesiosis may be gaining ground in parts of the Northeast and underscores the need to broaden diagnostic considerations.
Similar patterns are emerging beyond the U.S. In Sweden, a study of Ixodes ricinus ticks removed from humans found that among ticks infected with Babesia, nearly half were also co-infected with Borrelia. The implication is clear: Co-infection is not a regional anomaly, but part of a broader shift in tickborne disease ecology.
Why prevention matters even more now
As the number of pathogens carried by ticks increases, so does the importance of prevention. The U.S. Centers for Disease Control and Prevention (CDC) recommends avoiding wooded or brushy areas with tall grass and leaf litter, using Environmental Protection Agency (EPA)-registered insect repellents, and treating clothing and gear with permethrin. Checking for ticks after time outdoors, showering soon after coming inside, and promptly removing attached ticks are also key steps.
These measures have long been standard advice. But in an era of co-infection, their importance is heightened: A single missed tick bite may now carry more than one pathogen.
What could change next
Even as risks grow, new tools for prevention may be on the horizon. In March 2026, Pfizer and Valneva reported that their Phase 3 Lyme disease vaccine candidate demonstrated more than 70 percent efficacy in preventing confirmed Lyme disease in individuals aged five years and older. The companies said they intend to pursue regulatory submissions, marking one of the most significant advances in Lyme prevention in decades.
At the same time, researchers are exploring a fundamentally different strategy: stopping transmission at the level of the tick itself. New work has mapped how a tick’s nervous system regulates its salivary glands during feeding, offering insight into how tick saliva facilitates both blood feeding and pathogen transmission.
Broader efforts are also underway to expand the vaccine pipeline beyond Lyme disease. As outlined by an Infectious Diseases Society of America (IDSA) Science Speaks blog, multiple tickborne disease vaccines remain in development, but most are still in early stages, and no human vaccines are currently available in the U.S. Together, these developments point toward a future in which prevention extends beyond avoiding tick bites. Vaccines, combined with existing measures and potential new approaches targeting tick biology, could reshape how tickborne diseases are controlled.
Why this shift matters for clinicians
For clinicians, the implications are immediate. Long-term surveillance of tick populations is essential to understanding which pathogens are circulating and how often co-infections occur. The takeaway is straightforward: Suspected tickborne illness should not automatically be attributed to Lyme disease alone. Considering the possibility of co-infection can improve diagnostic accuracy and guide more appropriate treatment. As tick populations expand and the range of pathogens they carry continues to grow, both clinical awareness and prevention will become increasingly important.
Melvin Sanicas is an infectious disease physician.
