infectious diseases
Leptospirosis
Introduction
Leptospirosis is an infection caused by one of several pathogenic serotypes of the spirocheteLeptospira. Symptoms are biphasic. Both phases involve acute febrile episodes; the second phase sometimes includes hepatic, pulmonary, renal, and meningeal involvement. Diagnosis is by culture and serologic testing. Treatment is with antibiotics such asdoxycyclineorpenicillin. Spirochetes are distinguished by the helical shape of the bacteria. Pathogenic spirochetes includeTreponema,Leptospira, andBorrelia. BothTreponemaandLeptospiraare too thin to be seen using brightfield microscopy but are clearly seen using darkfield or phase microscopy.Borreliaare thicker and can also be stained and seen using brightfield microscopy. Leptospirosis, a zoonosis occurring in many domestic and wild animals, may cause inapparent illness or serious, even fatal disease in humans. Human infections are rare in the US. Leptospiraare maintained in nature through chronic renal infection of carrier animals—commonly rats, dogs, cattle, horses, sheep, goats, and pigs. These animals can shed leptospires in their urine for years. Dogs, cattle, pigs, mice, and rats are probably common sources of human infection. Human infections are acquired by direct contact with infected urine or tissue or indirectly by contact with contaminated water or soil. Abraded skin and exposed mucous membranes (conjunctival, nasal, oral) are the usual entry portals. Aerosol inhalation of droplet nuclei is a less common mode of entry. Leptospirosis can be an occupational disease (eg, of farmers or sewer and abattoir workers), but in the US, most patients are exposed incidentally during recreational activities (eg, swimming in contaminated fresh water). Outbreaks have been reported outside the US after heavy rainfall or freshwater flooding.Leptospiracan survive for several weeks to months in freshwater sources (eg, lakes, ponds). However, they can survive for only a few hours in salt water. Cases of leptospirosis in the US must be reported to the Centers for Disease Control and Prevention (CDC). The 100 to 200 reported annual US cases (highest incidence is in Puerto Rico followed by Hawaii) occur mainly in late summer and early fall. Because distinctive clinical features are lacking, probably many more cases are not diagnosed and reported. 