Illustration of Leptospira interrogans, showing a tightly-coiled, highly motile spirochaete bacterium. Pathogenic serotypes of L. interrogans cause the disease leptospirosis in humans, characterized by fever, vomiting, conjunctivitis and muscular pains. Jaundice and kidney failure may occur in the severe form of infection known as Weil's disease. Rodents are the main carriers, also dogs and farm animals: farmers, sewage workers and vets. Penicillin is the antibiotic of choice for treatment.