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Leptospira
Leptospirosis is a common and widespread zoonosis caused by aerobic, motile spirochetes of the genus Leptospira.
Etiology
Leptospira spp. are thin, helix-shaped members of the phylum Spirochaetes. There are 22 species identified within the genus Leptospira , and these are further divided into over 300 serovars. There are at least 10 pathogenic Leptospira species, with serovars demonstrating preferential host specificity.
Epidemiology
Leptospirosis has a worldwide distribution, but most human cases occur in tropical and subtropical countries with disease burden disproportionately affecting resource-poor populations. Leptospires survive for days to weeks in warm and damp environmental conditions, including water and moist soil. In the United States, the CDC estimates 100-200 annual cases; Hawaii reports about 50% of US cases, with Pacific coastal and Southern states having higher incidence than the remainder of the country. Leptospires infect many species of animals, including rats, mice, and moles; livestock such as cattle, goats, sheep, horses, and pigs; wild mammals like raccoons or opossums; and domestic dogs. Infected animals excrete spirochetes in their urine for prolonged periods. Globally, most human cases result from exposure to water or soil contaminated with rat urine; however, the major animal reservoir in the United States is the dog. Groups at high risk for leptospirosis include persons exposed occupationally or recreationally to contaminated soil, water, or infected animals. High-risk occupations include agricultural workers, veterinarians, abattoir workers, meat inspectors, rodent control workers, laboratory workers, sewer workers, and military personnel. Exposure to contaminated floodwaters is also a documented source of infection. Transmission via animal bites and directly from person to person has been rarely reported.
Pathology and Pathogenesis
Leptospires enter human hosts through mucous membranes (primarily eyes, nose, and mouth), transdermally through abraded skin, or by ingestion of contaminated water. After penetration, they circulate in the bloodstream, causing endothelial damage of small blood vessels with secondary ischemic damage to end organs.
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