Leptospirosis facts. 1  Leptospirosis is an infectious disease that can occur in humans and animals worldwide. 2  A spirochete, Leptospira interrogans, causes leptospirosis. 3  High risk factors include close association with animals and the water and soil they may contaminate with infected urine.eptospirosis is a disease caused by bacteria (Leptospira interrogans) that produce a wide range of symptoms that may occur in phases; some patients may develop kidney or liver failure, respiratory failure, meningitis, or even death.