Leptospirosis is caused by infection with the germs (bacteria) Leptospira. It is a type of zoonosis infection (an infection that can be passed from animals to humans). Both wild and domestic animals can become infected with Leptospira, including rats, cattle, pigs and dogs.n most cases, leptospirosis causes a mild illness. But, in some people, a more severe illness occurs. This more severe form is commonly referred to as Weil's disease. The main treatment for leptospirosis is antibiotics and most people make a full recovery.