Leptospirosis is a generalized infection of humans and animals caused by spirochetes of the genus Leptospira . The pathogenic leptospires belong to a single species, Leprospira interrogans , which contains approximately 200 distinct serovars. The organisms are aerobic bacteria, 6-20mum long and 0.1mum wide with terminal hooks. They can be visualized by darkfield examination and by silver impregnation staining. A special medium is required for their growth, and it may take weeks for cultures to become positive.
Leptospirosis is a zoonosis of worldwide distribution.
Leptospires infect many species of wild and domestic animals and have been isolated from birds, fish, and reptiles. The rat is the principal source of human infection. Other important animal reservoirs include dogs, cats, livestock, and wild animals. Animal infection varies from inapparent to fatal. Once infected, animals excrete spirochetes in urine for an extended period of time.