Lyme

Lyme disease is a bacterial infection caused by Borrelia burgdorferi sensu lato, transmitted to humans through bites of infected Ixodes ticks, commonly known as deer or blacklegged ticks. The disease is named after Lyme, Connecticut, where it was first described in 1975. In North America, Borrelia burgdorferi sensu stricto is the principal cause; in Europe and Asia, other members of the complex, such as B. afzelii and B. garinii, are more common.

Transmission typically occurs when an infected tick attaches for 24 to 48 hours. Ticks undergo a life cycle that includes larval, nymphal, and adult stages, with nymphs responsible for many human infections. The risk is highest in forested or grassy areas, and during warmer months when ticks are active. Prevention concentrates on reducing tick exposure and rapid removal of attached ticks.

Clinical features vary by stage. Early localized disease often presents with erythema migrans, a circular rash that expands over days and may be accompanied by fever, fatigue, and malaise. Early disseminated disease can include multiple rashes, facial nerve palsy, meningitis, radiculopathy, and carditis. Late disseminated Lyme disease may cause intermittent or chronic arthritis, particularly of the large joints, and occasional neurological or cognitive symptoms. Some individuals may have few or no early signs.

Diagnosis relies on clinical assessment and exposure history; laboratory testing uses a two-tier approach starting with an ELISA, followed by a Western blot. Serology may be negative in early infection. Polymerase chain reaction testing is not routinely used for blood samples but can aid in certain presentations.

Treatment involves antibiotics, typically doxycycline, amoxicillin, or cefuroxime for 14–28 days, with exceptions for children, pregnant women, or neurologic involvement who may require intravenous therapy such as ceftriaxone. Most patients recover with treatment; a subset reports lingering symptoms, sometimes labeled post-treatment Lyme disease syndrome. Prevention and education remain important components of management.