Development of chronic and acute golden Syrian hamster infection models with Leptospira borgpetersenii serovar Hardjo

The golden Syrian hamster (Mesocricetus auratus) is frequently used as a model to study virulence for several Leptospira species. Onset of an acute lethal infection following inoculation with several pathogenic Leptospira species has been widely adopted for pathogenesis studies. An important exception is the outcome following inoculation of hamsters with live L. borgpetersenii serovar Hardjo, the primary cause of bovine leptospirosis and a cause of human infections. Typically, inoculation of hamsters with L. borgpetersenii serovar Hardjo fails to induce clinical signs of infection. In this study, the authors defined LD(50) and ID(50) for 2 strains of L. borgpetersenii serovar Hardjo: JB197 and 203. Both strains infected hamsters with ID(50) values of approximately 1.5 × 10(2) bacteria yet differed in tissue invasion and interaction with leukocytes, resulting in widely divergent clinical outcomes. Hamsters infected with strain 203 established renal colonization within 4 days postinfection and remained asymptomatic with chronic renal infections similar to cattle infected with serovar Hardjo. In contrast, hamsters infected with strain JB197 developed a rapidly debilitating disease typical of acute leptospirosis common in accidental hosts (eg, humans) with an LD(50) of 3.6 × 10(4) bacteria. Evidence that strain JB197 resides in both extracellular and intracellular environments during hamster infection was obtained. Development of models that result in chronic and acute forms of leptospirosis provides a platform to study L. borgpetersenii pathogenesis and to test vaccines for the prevention of leptospirosis.