What Percentage of Ticks Have Lyme Disease?

What Percentage of Ticks Have Lyme Disease? (How Many Ticks Carry Lyme Disease)

In highly endemic regions of the northeastern United States, studies have found that roughly 25–60% of deer ticks (Ixodes scapularis) may carry Borrelia burgdorferi, the bacterium that causes Lyme disease. Infection rates vary by region, tick species, and life stage.

As the authors point out, “Concurrent polymicrobial infections in humans can have a synergistic effect and result in a more severe course of illness.”

In an effort to investigate what percentage of ticks have Lyme disease and other pathogens, researchers examined three tick species, including the deer tick (Ixodes scapularis), collected in Suffolk County, Long Island.

Their study revealed that over half of the deer ticks (63%) were infected with at least one pathogen.

This means that a single tick bite may expose a person to more than one infection at the same time.

“Borrelia burgdorferi was the most prevalent pathogen (57% in adults; 27% in nymphs), followed by Babesia microti (14% in adults; 15% in nymphs), Anaplasma phagocytophilum (14% in adults; 2% in nymphs), Borrelia miyamotoi (3% in adults), and Powassan virus (2% in adults),” writes Sanchez-Vicente.

These findings highlight the complex ecology of tick-borne infections. A single tick bite may transmit more than one pathogen, which can complicate both diagnosis and treatment.

Dual infections were detected in 19% of the I. scapularis ticks, while triple infections were detected in 3% of the ticks.

“Of note is that nearly one-quarter of the I. scapularis ticks tested had polymicrobial infections,” writes Sanchez-Vicente, “and this justifies the modification of the clinical approach to tick-borne diseases to cover all infection possibilities.”

These findings reinforce growing recognition that tick-borne coinfections are common and can influence both disease severity and recovery patterns.

[bctt tweet=”Polymicrobial infections represent another aspect of tick-borne diseases that can complicate diagnosis and augment disease severity.” username=”DrDanielCameron”]

Several pathogens detected in this study—including Anaplasma, Babesia, and Ehrlichia—infect blood cells and in rare cases may also be transmitted through blood transfusions.

This warrants concern given that the ratio of Lyme disease cases to babesiosis cases has been approximately 4 to 1 for the last eight years. “This ratio also holds for the ratio of B. burgdorferi to B. microti in ticks in this study, i.e., 3.8 to 1,” the authors write.

For a broader overview of overlapping infections transmitted by ticks, see our discussion of Lyme disease coinfections and Babesia and Lyme disease.

Are Most Deer Ticks Infected With Lyme Disease?

No. Infection rates vary widely depending on geography and the stage of the tick. In some highly endemic areas of the northeastern United States, studies have found that over half of adult deer ticks may carry Borrelia burgdorferi or another tick-borne pathogen, while infection rates in nymph ticks are generally lower.