La leptospirose : Les défis actuels d'une ancienne maladie

Leptospirosis is an infectious disease which affects man and animals, and is considered as the most common zoonosis worldwide. Every year, it is responsible for serious epidemics in tropical and developing countries. The pathogen is Leptospira interrogans, an extremely mobile and helicoidal spirochete. The clinical presentation of leptospirosis varies due to the diversity within the genus Leptospira and its complex epidemiology. Several mammal species may develop leptospirosis, mainly in its chronic form, and thus act as reservoirs for the disease. Human leptospirosis, or Weil’s disease, has a high mortality rate and is caused by Leptospira interrogans serogroup Icterohaemorrhagiae. The vaccination of man and animals has limited effects because vaccines are specific to the serovar and induce only a short-term immunity. The microagglutination test (MAT) used for the diagnosis of leptospirosis also has limitations, such as the inability to identify the early stage of the disease. However, progress is expected in diagnostic procedures, as the recently sequenced genome of Leptospira and the development of specific genetic tools mark the beginning of the post-genomic era in research on spirochetes. Our efforts are currently turned towards the understanding of leptospiral virulence mechanisms, as well as the development of more effective vaccines and diagnostic tests. The Spirochetes’ Biology Unit at Institut Pasteur, Paris, has just identified the first leptospiral virulence factor, Loa22, a protein of the OmpA family exposed on the cell surface of the bacteria. Loa22 is a candidate for the development of a vaccine.