SUBCUTANEOUS AND CONJUNCTIVAL VACCINATION WITH A LIVE ATTENUATED STRAIN OF SALMONELLA-ABORTUSOVIS - EFFECT OF GESTATION ON SEROLOGICAL RESPONSE OF EWES

Annual serological testing of flocks vaccinated by the subcutaneous ro ute with a live, attenuated strain of Salmonella Abortusovis has previ ously demonstrated the persistence of agglutinating antibodies. It has however been impossible to determine whether the antibodies originate d from the vaccination or from an enzootic infection. The serological response, as measured by a microtechnique of seroagglutination using a stained antigen, was studied in an isolated flock of 30 adult ewes. T he trial period after the subcutaneous vaccination was 34 months, whic h included 3 lambings. Ten female offspring of these ewes were also st udied. They were vaccinated by the conjunctival route and were studied for 18 months, which included 1 lambing. As is common for natural or experimental infection, high antibody titers were obtained 10-15 d aft er vaccination in both groups. The values then decreased and rose agai n to significant levels at each subsequent pregnancy. the vaccinal str ain was never isolated from vaginal swabs taken at each lambing and th ere was no suggestion of stimulation by an external antigen. Gestation may therefore stimulate the antibody response. This suggests that the immunity conferred by this vaccination may last for at least 3 lambin g periods. The consequences of these observations on vaccination proto cols and serological diagnosis are discussed.