Immunising potency of Leptospira interrogans serotype canicola after heat inactivation at different temperatures

The immunogenicity of Leptospira interrogans serotype canicola suspensions inactivated by various degrees of heat exposure was examined in hamsters. No differences between leptospires killed at 50 degrees C and at 98 degrees C were shown. After exposure to 121 degrees C, suspensions retained their ability to protect against lethal infections but lost their ability to prevent leptospiruria. Tests with vaccines inactivated at or below 98 degrees C showed that the doses required for complete protection varied with the interval between vaccination and challenge. Larger doses were required to prevent the development of leptospiruria than to prevent death.