If your pet has become infected, it most likely came into contact with the bacteria in the environment or was exposed to infected animals. Your pet may have been drinking, swimming, or walking through contaminated water. Because of increased building and development into areas that were previously rural, pets may be exposed to more wildlife, such as raccoons, skunks, squirrels, opossums, or deer that are infected with leptospirosis. Dogs also may pass the disease to each other, but this happens very rarely.