Lyme disease

Overview

Lyme disease is a bacterial infection caused by Borrelia burgdorferi, transmitted through bites from infected deer ticks (Ixodes species). Most cases follow a distinctive expanding skin rash called erythema migrans. When caught early, Lyme disease is readily treated with antibiotics. Late disseminated disease can affect the nervous system, heart, and joints.

How common is it?

Lyme disease is the most common vector-borne disease in the Northern Hemisphere. In the UK, approximately 2,000 to 3,000 laboratory-confirmed cases are reported annually, but actual incidence is likely higher. High-risk areas include the Scottish Highlands, the New Forest, and the South Downs.

Causes and risk factors

Infected ticks must be attached for 36 to 48 hours to transmit infection reliably. Most people who develop Lyme disease do not recall a tick bite.

Common risk factors

• Walking or working in wooded, heathland, or long-grass environments
• Outdoor activities: camping, gardening, hillwalking
• Tick attachment for more than 24 to 48 hours
• Ticks are most active from April to October
• Not immediately removing attached ticks
• Living in or visiting endemic areas

Symptoms

• Early localised (days 3 to 30): erythema migrans rash (expanding red ring, often with central clearing, warm but not usually painful) at the bite site, with flu-like symptoms
• Early disseminated (weeks): multiple erythema migrans lesions, facial nerve palsy (Bell's palsy), meningitis, heart block (Lyme carditis)
• Late disseminated (months to years): Lyme arthritis (large joint oligoarthritis, especially knees), encephalopathy

When to see a doctor

See a doctor promptly for an expanding rash at the site of a tick bite. Treatment should not wait for blood test results in this situation. Neurological symptoms (facial palsy, severe headache, limb weakness) or palpitations after a potential tick bite require urgent assessment.

Diagnosis

Erythema migrans is a clinical diagnosis — do not wait for serology. ELISA for Borrelia antibodies (low sensitivity in early disease) confirmed by Western blot. Antibodies may take 4 to 6 weeks to develop. Serology should not be used to diagnose or exclude Lyme disease in the first 4 weeks.

Treatments

Self-care and lifestyle

• Use insect repellent containing DEET (20 to 50%) on skin and clothing when in tick-prone areas
• Wear long sleeves and tuck trousers into socks in woodland
• Shower and perform a whole-body tick check after outdoor activities
• Check pets for ticks as they can bring ticks into the home

Prevention

Tick avoidance, prompt tick removal, and DEET use are the most effective preventive measures. There is no licensed human Lyme disease vaccine currently available in the UK, though one is in late-stage trials.