Lyme disease

Lyme disease is a bacterial infection transmitted by the bite of infected black-legged (deer) ticks. It is the most common tick-borne illness in many temperate regions of the Northern Hemisphere. Early symptoms often include fever, fatigue, headache, and a characteristic expanding rash called erythema migrans.

When treated promptly with antibiotics, most people recover fully. Delayed treatment can allow the bacteria to spread to joints, the heart, and the nervous system. Prevention focuses on avoiding tick bites and removing ticks quickly. A vaccine is not currently widely available for humans in all regions, though research continues.

Lyme disease can progress through stages:

Early localized (days to weeks after the bite):

• Erythema migrans — an expanding red rash, sometimes with a “bull’s-eye” appearance; not always present and not always annular
• Fever, chills, fatigue, body aches, headache, swollen lymph nodes

Early disseminated (weeks to months):

• Additional rashes
• Facial palsy (Bell’s palsy), meningitis symptoms, radiculoneuritis
• Heart block or other cardiac involvement
• Severe joint pain and swelling, often migratory

Late disease:

• Intermittent or persistent arthritis, typically of large joints (especially the knee)
• Rarely, chronic neurologic problems

Not everyone recalls a tick bite or notices a rash.

Lyme disease is caused by spirochetal bacteria of the Borrelia burgdorferi sensu lato complex (B. burgdorferi in North America; additional species in Europe and Asia). Transmission occurs through the bite of infected Ixodes ticks. Ticks must usually be attached for 36–48 hours or more to transmit the bacteria. The ticks acquire the bacteria by feeding on infected reservoir animals (especially white-footed mice and other small mammals).

Risk is highest for people who:

• Live in, work in, or visit wooded, brushy, or grassy areas in endemic regions
• Have outdoor occupations or recreational activities (hiking, hunting, gardening)
• Have pets that can carry ticks into the home
• Do not use tick-prevention measures

Seasonality peaks in warmer months when nymphal ticks are active.

Possible complications of untreated or partially treated Lyme disease include:

• Lyme arthritis (can rarely persist after antibiotics due to immune response)
• Neurologic disease (meningitis, radiculopathy, neuropathy, rare encephalopathy)
• Lyme carditis with heart block (can be fatal in rare cases if untreated)
• Post-treatment Lyme disease symptoms — fatigue, pain, or cognitive complaints persisting after appropriate treatment (management is supportive; prolonged antibiotics are not beneficial for most)

Key preventive steps:

• Avoid wooded and brushy areas with high grass when possible; stay on cleared paths
• Use EPA-registered repellents (DEET, picaridin, IR3535, oil of lemon eucalyptus, etc.) on skin and permethrin on clothing and gear
• Wear long sleeves and pants; tuck pants into socks in high-risk areas
• Check clothing, body, and pets for ticks after being outdoors; shower soon after coming indoors
• Remove attached ticks promptly with fine-tipped tweezers — grasp close to the skin and pull upward steadily
• Create tick-safe zones in yards (clear brush, keep grass short)

Early Lyme disease with typical erythema migrans in an endemic area is often diagnosed clinically; blood tests may still be negative early on. For disseminated or later disease, two-tier serologic testing (ELISA followed by Western blot or a modified two-tier algorithm with two EIAs) is the standard. PCR of joint fluid may help in Lyme arthritis. Testing should be guided by pretest probability; indiscriminate testing of asymptomatic people is not recommended.

See a clinician if you develop a expanding rash, flu-like illness after possible tick exposure, or unexplained facial palsy, joint swelling, or heart symptoms in an endemic area. Early evaluation allows timely treatment. If you find an attached tick, remove it promptly; discuss with a clinician whether preventive antibiotics are appropriate based on geography, tick type, and attachment time.

Antibiotics are curative in the large majority of cases:

• Early disease — oral doxycycline, amoxicillin, or cefuroxime for 10–14 days (duration and agent depend on age, pregnancy, and presentation)
• Neurologic or cardiac disease — often intravenous ceftriaxone for more serious involvement; oral regimens for some milder neurologic presentations
• Lyme arthritis — oral or IV antibiotics; persistent joint inflammation after antibiotics may need anti-inflammatory management rather than repeated long antibiotic courses
• Single-dose doxycycline may be offered after a high-risk tick bite in selected endemic settings as post-exposure prophylaxis

Follow recommended regimens; longer courses have not been shown to improve outcomes for post-treatment symptoms and increase side effects.

During treatment:

• Take the full antibiotic course as prescribed
• Rest as needed and stay hydrated
• Use pain relievers for joint or muscle discomfort if approved by your clinician
• Watch for medication side effects (including photosensitivity with doxycycline — use sun protection)
• Return for care if symptoms worsen or new neurologic or cardiac symptoms develop
• Continue tick-prevention habits to avoid reinfection

Bring:

• History of possible tick exposure, travel, or outdoor activities
• Description and photos of any rash
• Timeline of fever, joint, neurologic, or cardiac symptoms
• Previous Lyme tests or antibiotic treatments
• Questions about testing interpretation, treatment duration, and prevention