Leptospirosis is a disease that infects dogs, humans and other animals. The organism that causes the disease is a type of bacterium called spirochete. Leptospirosis is spread by recovered animals that shed the spirochete in their urine for months to years following infection. Exposure to the disease usually occurs in the environment from contaminated water, food, soil, or vegetation. The Leptospirosis organism penetrates through the interior lining of the mouth (mucosa) or through injured skin. Wild animals, especially rats, are carriers of the disease.