What bacteria causes Lyme disease?

Q: What bacteria causes Lyme disease?

Lyme disease is a bacterial infection caused by *Borrelia* bacteria, most commonly *Borrelia burgdorferi* in the United States. It spreads to humans through the bite of infected blacklegged ticks (deer ticks). Early symptoms often include a bullseye-shaped rash, fever, fatigue, headache, and joint pain. If left untreated, the infection can spread to the joints, heart, and nervous system. Because Lyme disease symptoms can mimic many other conditions—like the flu, arthritis, or chronic fatigue—early identification is critical to getting the right treatment and avoiding long-term complications. If you've noticed unusual symptoms after a possible tick exposure, or you're simply unsure what's causing how you feel, taking a free, instant, online symptom check can help you understand what may be going on and guide your next steps with confidence. Reviewed for medical accuracy: 07/15/2026

Reviewed by Yoshinori Abe, MD

Internal Medicine

Lyme disease is a bacterial infection caused by Borrelia bacteria, most commonly Borrelia burgdorferi in the United States. It spreads to humans through the bite of infected blacklegged ticks (deer ticks). Early symptoms often include a bullseye-shaped rash, fever, fatigue, headache, and joint pain. If left untreated, the infection can spread to the joints, heart, and nervous system.

Because Lyme disease symptoms can mimic many other conditions—like the flu, arthritis, or chronic fatigue—early identification is critical to getting the right treatment and avoiding long-term complications. If you've noticed unusual symptoms after a possible tick exposure, or you're simply unsure what's causing how you feel, taking a free, instant, online symptom check can help you understand what may be going on and guide your next steps with confidence.

Reviewed for medical accuracy: 07/15/2026

Important Next Steps

Discover if Lyme disease could explain symptoms Learn whether your symptoms need care today Find likely causes of possible Lyme infection See OTC options for tick-bite symptoms Find a doctor for Lyme disease care Discover home remedies for tick-bite discomfort Understand if your symptoms need urgent care

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Explanation

Lyme disease is an illness caused by bacteria from the Borrelia group. In the United States, the main bacteria that causes Lyme disease is called Borrelia burgdorferi. When a person is bitten by a tick that carries these bacteria, they can get Lyme disease.

Key Points:

Cause: The bacteria responsible for Lyme disease are known as Borrelia. In the U.S., Borrelia burgdorferi is the most common cause.
Transmission: Lyme disease is spread through the bite of infected ticks.
Symptoms: People with Lyme disease might get a rash, fever, headache, or feel tired.

Understanding the bacteria that cause Lyme disease helps doctors know how to treat it and prevent it from spreading. If you spend time in areas where ticks live, it is important to check for ticks and remove them quickly to lower the risk of getting Lyme disease. If you're experiencing any concerning symptoms after a tick bite or potential exposure, you can use a free symptom checker to help assess your condition and determine if you should seek medical care.

(References)

Chomel B. (2015). Lyme disease. Revue scientifique et technique (International Office of Epizootics), 26601457.
Marques AR, Strle F, & Wormser GP. (2021). Comparison of Lyme Disease in the United States and .... Emerging infectious diseases, 34286689.
Steere AC, Strle F, Wormser GP, Hu LT, Branda JA, Hovius JW, et al. (2016). Lyme borreliosis. Nature reviews. Disease primers, 27976670.

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