The development of a potency test for Leptospira hardjo vaccines: a comparison of protection in calves and serology in guinea-pigs.

The protective properties of two commercial Leptospira hardjo vaccines in calves were compared with the serological responses induced in guinea-pigs with a view to establishing a potency test based on serology. Groups of calves were given graded doses of the two vaccines and after eight weeks were challenged with virulent L. hardjo. Infection was monitored by microscopy and culture of urine and, eight weeks after challenge, by culture of the kidneys post mortem. Groups of guinea-pigs also were tested by the microscopic agglutination test (MAT). A clear dose response was observed and the response was related to the degree of protection achieved in the calves. The MAT titre in guinea-pigs indicative of an effective vaccine was calculated for the minimum dose of each vaccine that gave full protection in calves. A close correlation was observed. Two further batches of each vaccine were tested in guinea-pigs on two occasions with reproducible results. A potency test based on the MAT response of guinea-pigs is proposed.