Leptospirosis (also known as Weil's disease, canicola fever, canefield fever, nanukayami fever, 7-day fever and many more blank">Weil Syndrome ) is a bacterial zoonotic disease caused by spirochaetes of the genus Leptospira that affects humans and a wide range of animals, including mammals, birds, amphibians, and reptiles. It was first described by _Adolf Weil in 1886 when he reported an "acute infectious disease with enlargement of spleen, jaundice and nephritis". Leptospira was first observed in 1907 from a post mortem renal tissue slice.

Though being recognised among the world's most common zoonoses, leptospirosis is a relatively rare bacterial infection in humans. The infection is commonly transmitted to humans by allowing fresh water that has been contaminated by animal urine to come in contact with unhealed breaks in the skin, eyes or with the mucous membranes. Outside of tropical areas, leptospirosis cases have a relatively distinct seasonality with most of them occurring August-September/February-March.