Use of a monovalent leptospiral vaccine to prevent venal colonization and urinary shedding in cattle exposed to Leptospira borgpetersenii serovar hardjo

Objective-To determine whether a monovalent Leptospira borgpetersenii serov ar hardjo (type hardjobovis) vaccine commercially available in Australia, N ew Zealand, Ireland, and the United Kingdom would protect cattle from renal colonization and urinary shedding when exposed to a US strain of Leptospir a borgpetersenii serovar hardjo. Animals-24 Hereford heifers that lacked detectable antibodies against serov ar hardjo. Procedure-Heifers received 2 doses, 4 weeks apart, of the commercial hardjo vaccine (n = 8) or a monovalent US reference hardjo vaccine (8) or were no t vaccinated (controls; 8). Heifers were challenged 16 weeks later by intra peritoneal inoculation or conjunctival instillation. Serum antibody titers were measured weekly, and urine samples were examined for leptospires, Heif ers were euthanatized 11 to 14 weeks after challenge, and kidney tissue was examined for evidence of colonization. Results-All 8 heifers vaccinated with the reference vaccine were found to b e shedding leptospires in their urine and had evidence of renal colonizatio n. All 4 control heifers challenged by conjunctival instillation and 2 of 4 control heifers challenged by intraperitoneal inoculation shed leptospires in their urine, and all 8 had evidence of renal colonization. In contrast, leptospires were not detected in the urine or tissues of any of the 8 heif ers that received the commercial hardjo vaccine. Heifers that received the commercial hardjo vaccine had significantly higher antibody titers than did heifers that received the reference vaccine. Conclusions and Clinical Relevance-Results suggest that cattle that receive d 2 doses of the commercial hardjo vaccine were protected against renal col onization and urinary shedding when challenged with L borgpetersenii serova r hardjo strain 203 four months after vaccination.