Leptospirosis

Leptospires are thin, tightly coiled spirochaetes with hooked ends, visualized by darkfield microscopy rather than Gram stain. Rats and other mammals shed the organism in urine, and humans are infected through mucous membranes or abraded skin during exposure to fresh water, making it a hazard of flooding, sewage work, farming, and water sports; it is endemic in Hawaii and in tropical regions. The first, leptospiraemic phase gives abrupt high fever, rigors, severe myalgia of the calves, headache, and conjunctival suffusion; after a brief defervescence the second, immune phase brings aseptic meningitis and, in severe cases, Weil disease with jaundice out of proportion to transaminase elevation, acute kidney injury, haemorrhage, and pulmonary haemorrhage. A hallmark laboratory pattern is markedly raised bilirubin with only modest transaminases, plus thrombocytopenia and creatine kinase elevation. Treatment is doxycycline for mild disease and intravenous penicillin or ceftriaxone for severe; a Jarisch-Herxheimer reaction may follow.