What is Lyme Disease?

A clear, evidence-based guide to Lyme disease — causes, symptoms, diagnosis, treatment, and long-term outcomes.

Can Lyme disease tests be negative early on?

Yes. Antibody tests may be negative in the first few weeks of infection. If clinical suspicion remains high and early tests are negative, repeat testing is recommended after a few weeks.

Infections

Lyme Disease

2025-11-18

Intro

Lyme disease is a bacterial infection caused by Borrelia burgdorferi and transmitted through the bite of infected Ixodes ticks (black-legged or deer ticks). Early detection and treatment are highly effective. Without treatment, the infection can spread to joints, nerves, and the heart.

Key Points

Caused by Borrelia burgdorferi (and in Europe, B. afzelii and B. garinii).
Spread through Ixodes ticks; transmission usually requires ≥36–48 hours of attachment.
Early symptoms include erythema migrans (bull’s-eye rash), fever, fatigue, and muscle aches.
Diagnosed with clinical assessment + two-tier serology.
Most cases respond well to 10–28 days of antibiotics.
A small group experience persistent symptoms (post-treatment Lyme disease syndrome), but active infection is rarely found.

Where Lyme Disease Is Most Common

Tick-borne risk

Lyme disease risk is highest in temperate regions of North America, Europe, and parts of Asia where Ixodes ticks are established. Risk can change over time as tick habitats expand.

Map is schematic and for educational use only. For regional risk and current surveillance data, see CDC, ECDC and national surveillance reports .

Background

Lyme disease is the most common tick-borne infection in North America and Europe. Risk is seasonal (spring–autumn) and linked to wooded and grassy areas where ticks feed on small mammals and deer.

Causes or Mechanisms

Lyme disease is caused by spirochete bacteria transmitted during a tick blood meal. Once inside the body, Borrelia spreads through the skin and bloodstream, causing local inflammation and sometimes disseminating to other organs.

Tick attachment under 24 hours has very low transmission risk; the likelihood rises sharply after 36–48 hours.

Diagnosis / Treatment / Options

Diagnosis

Diagnosis uses a combination of:

Clinical signs (particularly the erythema migrans rash — no test needed)
Two-tier serology:
- ELISA screening test
- Western blot confirmation

PCR is occasionally used for joint fluid but is not standard for blood.

Treatment

Standard antibiotic courses (examples):

Doxycycline 100 mg twice daily for 10–21 days
Amoxicillin or cefuroxime for those who cannot take doxycycline
IV ceftriaxone for some neurological or cardiac cases

Longer or repeated antibiotic courses are not proven effective and carry risks (C. difficile, line infections).

Risks / Benefits / Prognosis

With early treatment, prognosis is excellent.
Joint inflammation (Lyme arthritis) can take months to fully resolve even after the infection is cleared.
Post-treatment Lyme disease syndrome (PTLDS) affects a minority (fatigue, pain, brain fog) but does not imply ongoing infection.
Cardiac involvement is rare and usually reversible with treatment.

What To Do After a Tick Bite

What to Do After a Tick Bite

Decision guide

Step 1: Remove the tick

Use fine-tipped tweezers to grasp the tick close to the skin and pull upwards with steady pressure. Clean the area with soap and water or antiseptic.
Step 2: Estimate how long the tick was attached

If the tick is flat and you are confident it was attached <24 hours, the risk of Lyme transmission is very low. Engorged ticks or uncertain duration (>36–48 hours possible) carry higher risk.
Step 3: Watch for symptoms in the next 30 days

Look for an expanding red rash (especially a “bull's-eye”), fever, fatigue, headache, or new joint or nerve symptoms. Take a photo of any rash and note the date.
Step 4: When to seek medical advice urgently
- Any expanding rash at or near the bite site
- Fever, flu-like illness, or severe headache
- Facial drooping, weakness, or palpitations
- Tick attached >36–48 hours in a high-risk region
Step 5: Prophylactic antibiotics (where recommended)

In some regions, a single dose of doxycycline is offered after a high-risk bite (Ixodes tick, attached ≥36 hours, started within 72 hours of removal). This decision should be made with a clinician familiar with local guidelines.

This flowchart is for general education only and does not replace individual medical advice. Local guidelines and tick-borne diseases vary by country.

FAQ

Q: Can you get Lyme disease without seeing a tick?
A: Yes. Many people never notice the tick.

Q: Is chronic Lyme disease real?
A: Persistent symptoms after treatment exist (PTLDS), but prolonged active infection has not been demonstrated in well-controlled studies.

Q: Can blood tests be negative early on?
A: Yes. Early serology may be negative; repeat testing is recommended if suspicion remains high.