Lyme disease
A bacterial infection spread by the bite of an infected tick. It often starts with an expanding 'bull's-eye' rash and flu-like symptoms; if untreated it can later affect the joints, nervous system and heart. Caught early, it is treated effectively with antibiotics.
What it is
Lyme disease is an infection caused by Borrelia bacteria, transmitted to people through the bite of an infected tick — most often after time spent in grassy or wooded areas. It typically unfolds in stages. Early on, days to a few weeks after the bite, many people develop a characteristic slowly expanding rash called erythema migrans — often, though not always, with a clearer centre giving a 'bull's-eye' appearance — sometimes with flu-like symptoms of fever, tiredness, headache and aching. At this stage, treatment is highly effective. If the early infection is missed or untreated, the bacteria can spread over weeks to months, leading to later features: migrating joint pains and swelling (Lyme arthritis, often the knee), nerve involvement (such as a facial droop or nerve pains), and, less commonly, effects on the heart's rhythm. Diagnosis rests heavily on the clinical picture and a realistic history of tick exposure: the classic bull's-eye rash is enough to diagnose and treat without a blood test, because antibodies may not have developed that early. In later disease, two-tier antibody blood tests support the diagnosis. Treated with antibiotics, most people recover fully; a minority have lingering symptoms afterwards. Prevention — avoiding bites and removing ticks promptly — is important where Lyme is common.
Key lab markers
- Lyme antibody serology — a two-tier test (screening ELISA confirmed by Western blot); supports later-stage disease but may be negative very early.
- ESR and CRP — inflammatory markers, sometimes raised, non-specific.
- Joint fluid analysis — if Lyme arthritis is suspected.
- Note — the classic bull's-eye rash is diagnosed clinically and treated without waiting for blood tests.
Symptoms
- An expanding 'bull's-eye' or oval rash at a bite site (erythema migrans)
- Flu-like symptoms: fever, tiredness, headache, muscle and joint aches
- Later: migrating joint pain and swelling, often the knee
- Nerve problems, such as facial drooping or nerve pains
- Less commonly, heart-rhythm disturbances
- A history of tick exposure or time in grassy/wooded areas
Related symptoms
Related lab panels
When to discuss with a doctor
See a doctor promptly if you develop an expanding bull's-eye rash after possible tick exposure, or flu-like symptoms following a tick bite — early Lyme disease is treated effectively with antibiotics, and the classic rash is enough to start treatment without waiting for a blood test. Later symptoms such as a swollen, painful joint that migrates, a new facial droop, or nerve pains after possible tick exposure also warrant assessment. Because Lyme serology can be negative very early and stays positive long after successful treatment, it is interpreted with the clinical picture rather than used alone or to monitor recovery. Removing an attached tick promptly and correctly lowers the risk. Mediora.AI can show Lyme antibody and inflammatory results in context, but whether they reflect active disease, and any treatment, is a clinical decision for your doctor with your symptoms and exposure history.