What Percentage of Ticks Have Lyme Disease?
“What are the chances this tick carried Lyme disease?”
This is one of the most common questions after a tick bite.
Quick Answer: In highly endemic regions of the northeastern United States, approximately 25–60% of deer ticks (Ixodes scapularis) may carry Borrelia burgdorferi, the bacterium that causes Lyme disease.
Clinical Insight: A single tick bite may expose a person to more than one infection, which can complicate both diagnosis and treatment.
In some regions, infection rates are even higher when all pathogens are considered—not just Lyme disease.
What percentage of ticks carry Lyme disease?
In one study of ticks collected in Suffolk County, Long Island, researchers found:
- 57% of adult ticks carried Borrelia burgdorferi
- 27% of nymph ticks carried Borrelia burgdorferi
- 63% of ticks carried at least one pathogen
These findings show that in some areas, more than half of ticks may carry Lyme disease or another infection.
Ticks often carry more than one infection
Ticks are not limited to a single pathogen.
Researchers identified multiple infections in the same ticks, including:
- Babesia microti
- Anaplasma phagocytophilum
- Borrelia miyamotoi
- Powassan virus
Dual infections were found in 19% of ticks, while triple infections were found in 3%.
This means that a single tick bite may transmit more than one infection at the same time.
These patterns are discussed further in tick-borne coinfections and Babesia and Lyme disease.
Why coinfections matter
Coinfections can affect how illness presents and how patients respond to treatment.
As researchers note, polymicrobial infections may lead to more severe disease and complicate diagnosis.
This challenges the traditional “one microbe, one disease” model of infection.
Do all ticks carry Lyme disease?
No. Infection rates vary depending on:
- Geographic region
- Tick species
- Life stage (nymph vs. adult)
In highly endemic areas, adult ticks are more likely to be infected than nymphs.
In other regions, infection rates may be significantly lower.
Clinical takeaway
Not every tick carries Lyme disease—but in endemic areas, the risk is substantial.
More importantly, ticks often carry multiple pathogens, increasing the complexity of tick-borne illness.
Understanding these risks can help guide early evaluation and treatment decisions after a tick bite.
Frequently Asked Questions
What percentage of ticks have Lyme disease?
In endemic areas, approximately 25–60% of deer ticks may carry Lyme disease.
Do most ticks carry Lyme disease?
No. Infection rates vary by region, but in some areas, a significant percentage of ticks are infected.
Can one tick carry multiple diseases?
Yes. Many ticks carry more than one pathogen, including Babesia and Anaplasma.
Are nymph ticks less likely to carry Lyme disease?
Yes. Nymph ticks generally have lower infection rates than adult ticks.
Related Reading
Dr. Daniel Cameron, MD, MPH
Lyme disease clinician with over 30 years of experience and past president of ILADS.
Symptoms • Testing • Coinfections • Recovery • Pediatric • Prevention
