Waterborne Leptospirosis: Survival and Preservation of the Virulence of Pathogenic Leptospira spp. in Fresh Water

Many studies have implicated fresh water as a source of leptospirosis outbreaks. To estimate the survival and the preservation of the virulence of pathogenic Leptospira spp. maintained in water, we selected five still waters with various pH and mineral profiles. The water samples were artificially inoculated with a culture of a pathogenic strain belonging to serovar Icterohaemorrhagiae. Samples were stored for 20 months at 4, 20 or 30 A degrees C. The survival and preservation of virulence of this pathogenic strain was estimated by subculturing these stored samples. After 14 and 20 months of storage, the strain Icterohaemorrhagiae was re-isolated, and its virulence was determined using an animal model. In these waters, the mean survival was 130 days for storage at 4 A degrees C, 263 days at 20 A degrees C, and 316 days at 30 A degrees C. Unexpectedly, the mean survival was 344 days for a final pH < 7 and 129 days for pH a parts per thousand yen 7. Moreover, the pathogenic strain remained fully virulent and was able to induce a lethal disease in gerbils even when the pH of the contaminated waters decreased to < 6. These data showed that despite unfavourable storage conditions such as cold, nutrient-poor acidic waters, the survival and virulence of pathogenic Leptospira spp. was fully preserved over at least 20 months.