causes of leptospirosis
Causes of leptospirosis. Leptospirosis is caused by a strain of bacteria called leptospira, which is found in certain animals and can spread to humans. Many different kinds of animals can carry the bacteria, but it is most commonly associated with:1  rats and mice. 2  farm animals, such as pigs, cattle, horses and sheep.3  dogs.auses of leptospirosis. Leptospirosis is caused by a strain of bacteria called leptospira, which is found in certain animals and can spread to humans. Many different kinds of animals can carry the bacteria, but it is most commonly associated with: