Leptospirosis is any disease caused by a member of the bacterial genus Leptospira, which chiefly afflicts a number of livestock species and other domestic animals but can also affect humans. Common names for human leptospirosal diseases include spirochetal jaundice, Weil's disease, canicola fever, mud fever, swamp fever, hemorrhagic jaundice, infectious jaundice, and swineherd's disease.
The disease is spread by the urine of infected people and animals. It tends to infect people who handle animals or who come into contact with animal urine (either directly or through contaminated soil and water) or infected animal tissue. A common way of catching leptospirosis is by swimming or wading in ponds that animals have peed in.
Symptoms often include fever, headache, chills, and muscle pain, but can also include jaundice, bleeding and/or hemorrhaging in or below the skin, rash, meningitis, and kidney failure. The meningitis/kidney failure stage is characteristic of Weil's disease.
The incubation period for the illness is 2 to 28 days, and if it goes untreated, one can stay sick for several months. Weil's disease may be fatal if untreated. Leptospirosis is most often treated with oral antibiotics such as doxycycline or penicillin. However, if it's not caught early enough, intravenous antibiotics may be necessary.
Part of the information in this writeup was gleaned from http://www.cdc.gov/ncidod/dbmd/diseaseinfo/leptospirosis_g.htm. The rest was taken from work I wrote for the science dictionary at http://biotech.icmb.utexas.edu/.