Question
Lyme disease
Answer
Lyme disease is a tick-borne zoonotic infection caused by the spirochete Borrelia burgdorferi (and related genospecies), transmitted to humans by the bite of infected Ixodes ticks (the deer/black-legged tick), which acquire the organism from a reservoir of small mammals (notably rodents) and deer.
Clinical stages:
- Early localized stage: the pathognomonic erythema migrans — an expanding, annular, erythematous skin lesion with central clearing (“bull’s-eye” rash) at the site of the tick bite, appearing days to weeks after the bite, often with fever, malaise, and lymphadenopathy.
- Early disseminated stage (weeks to months): haematogenous spread producing multiple secondary erythema migrans lesions, neurological involvement (facial nerve palsy, lymphocytic meningitis, radiculoneuritis), and cardiac involvement (atrioventricular conduction block, myocarditis).
- Late stage (months to years): Lyme arthritis — recurrent or chronic large-joint (especially knee) mono/oligoarthritis; chronic neurological manifestations (encephalopathy, peripheral neuropathy) in a minority of untreated patients.
Laboratory diagnosis: primarily clinical in the erythema migrans stage; serology (two-tier testing — screening ELISA followed by confirmatory Western blot) for later/disseminated stages, since antibody response takes weeks to develop; PCR on synovial fluid/CSF in selected cases; direct culture is difficult and not routinely used.
Treatment: doxycycline (or amoxicillin/cefuroxime in children and pregnant women) for early localized/disseminated disease; intravenous ceftriaxone for neuroborreliosis or Lyme carditis.
Prevention: avoiding tick-infested areas, protective clothing, tick repellents, and prompt removal of attached ticks (transmission risk rises with duration of tick attachment).