Bull urine and semen as potential vectors of disease transmission for Leptospira borgpetersenii serovar Hardjo

Bovine leptospirosis can result in infertility, abortion, placentitis, weak offspring, stillbirths, and decreased milk production. The leading cause of bovine leptospirosis globally is Leptospira borgpetersenii serovar Hardjo. Asymptomatic cattle with leptospirosis serve as reservoir hosts of infection that can shed infectious leptospires for months to years. Sites of bacterial colonization include the kidney or the genital tract, or both, in both cows and bulls. In this observational study, we investigated leptospirosis in a herd of asymptomatic bulls; 24.1% (14/58) were shedding leptospires via urine as confirmed by lipL32 real-time PCR (rtPCR). The viability of leptospires in selected rtPCR-positive bull urine samples was confirmed by culture. Given that bovine semen may also act as a vector of disease transmission, we investigated frozen semen samples for evidence of leptospires; 1.5% (4/268) were lipL32 rtPCR-positive, and, of these, one was culture-positive. All isolates cultured from bull urine or semen were classified as L. borgpetersenii serogroup Sejroe serovar Hardjo. The viability and infectivity of the semen isolate were confirmed in the hamster model of leptospirosis. Our results report for the first time the ability to culture serovar Hardjo directly from frozen semen and highlight the potential role for bull urine and semen in the transmission of bovine leptospirosis.