Lyme disease — expanded notes
Organism and transmission
Lyme borreliosis is caused by Borrelia burgdorferi sensu lato and transmitted by Ixodes ticks. European species include B. afzelii and B. garinii. Infection risk increases with exposure to tick habitats; prompt removal reduces transmission risk.
Erythema migrans
Erythema migrans is an expanding erythematous lesion at the bite site, usually appearing days to weeks after exposure. It often exceeds 5 cm and expands over time; central clearing is not required. It may be warm but is often not painful. In an appropriate epidemiological setting, typical erythema migrans is diagnosed clinically because early serology can be negative.
Disseminated and late disease
- Early disseminated disease may cause multiple erythema migrans lesions, facial nerve palsy, lymphocytic meningitis, radiculoneuritis or carditis with atrioventricular block.
- Lyme arthritis usually causes intermittent or persistent swelling of a large joint, especially the knee.
- Late neurological manifestations are less common and require specialist assessment.
Testing
For typical erythema migrans, do not rely on serology. For other presentations, use validated two-tier serology. Antibodies may be absent early and can remain positive for years after resolved infection. Interpret results with exposure history and compatible clinical findings. PCR may be useful in selected specimens such as synovial fluid, not as a routine test for skin lesions.
Treatment and prevention
Treatment depends on manifestation, age, pregnancy and local guidance. Doxycycline or beta-lactam alternatives are used for uncomplicated erythema migrans; neurological disease, carditis and arthritis may require different regimens and specialist input. Prevent bites with protective clothing, repellents, body checks and prompt tick removal. Avoid prolonged antibiotic treatment for nonspecific persistent symptoms without evidence of active infection.