[Leptospirosis now-the centennial of the discovery of Weil's disease pathogen]

This year, 2014, marks the centennial of the discovery of Leptospira as the Weil's disease pathogen by Ryokichi Inada, Yutaka Ido and their colleagues. Leptospirosis is a worldwide zoonosis especially in countries with tropical and subtropical climates. Recently, the number of patients with leptospirosis dramatically decreased in Japan because public hygiene has greatly improved, the mechanization of agriculture was introduced, and farmers started using rubber boots and gloves while working in the field. The opportunities for percutaneous infection with Leptospira was reduced, but have not been totally eliminated in Japan.We previously reported a novel combination of five antimicrobial agents for selective isolation of Leptospira from contaminated samples. This cocktail, after being incorporated into Leptospira growth medium, inhibited the growth of contaminants and allowed successful detection of leptospires in environmental samples. We collected soil and environmental water and cultured them using this selective medium. It was revealed that not only saprophytic Leptospira but also pathogenic Leptospira are widely living in the environment. We hypothesized that soil serves as reservoir for Leptospira and infectious source for leptospirosis. In this review, we also discuss the Leptospira-rat-human relationship in the Philippines, natural defense of host against oral and percutaneous infection by Leptospira, the mechanism of jaundice in leptospirosis, and the development of immunochromatography-based methods for detection of leptospiral antigen in urine.