Association between cessation of leptospiruria in cattle and urinary antibody levels.

The shedding of Leptospira interrogans serovar hardjo in the urine of cattle and the local and systemic response to these organisms was monitored in experimentally and naturally infected animals. Twenty yearling heifers, 10 infected by the instillation of leptospires into the conjunctival sac (supraconjunctival route) and 10 infected intrauterinely, shed leptospires for up to 60 weeks after infection. Five of 15 naturally infected pregnant heifers with microscopic agglutination test titres > or = 1:300 continued to shed leptospires from 28 to 40 weeks after initial detection. Serovar hardjo was isolated infrequently from the urine of a further five naturally infected animals during the first eight weeks of the study but no leptospires were isolated from the remaining five animals for the duration of the study period (84 weeks). Cessation of leptospiruria in the 20 experimentally infected animals and in the five naturally infected persistent excretors was invariably associated with a sharp increase in urinary anti-leptospiral IgG and IgA antibody levels.