Essentially all mammals are susceptible to infection with pathogenicLeptospira, although some species are more resistant to disease. Among common companion animals and livestock, leptospirosis is most frequently recognized in cattle, swine, dogs, and horses. Cats seem to be relatively resistant to disease. Leptospirosis in wildlife is common, although the disease is most often noticed only when the wildlife serve as a source of infection for domestic animals or humans.
Leptospirosis occurs throughout the world. The infection and disease is more prevalent in warm, moist climates and is endemic in much of the tropics. In temperate climates, the disease is more seasonal with the highest incidence associated with periods of rainfall.