Vaccination of ewes by a single conjunctival administration of Brucella melitensis Rev. 1 vaccine

Abstract

In a lot of 99 ewes, the efficacy of a single vaccination by the conjunctival route (VC) with either 1.4 X 10(8) or 1.4 X 10(9) CFU Brucella melitensis Rev. 1 was compared with that of normal subcutaneous (SC) vaccination with 1.6 X 10(9) CFU. The ewes were challenged seven months after vaccination, when 85 days pregnant, with 5 X 10(7) CFU Brucella melitensis strain H38 administered by conjunctival route. Complement fixation, Rose Bengal and allergic tests were performed at intervals between vaccination and slaughter, and clinical and bacteriological examinations between challenge and slaughter, six weeks after lambing. After VC vaccination, few animals showed Brucella antibodies whatever the dose, and all were seronegative as early as four months after vaccination whereas a few SC vaccinated individuals were still seropositive at ten months. There were more allergic reactions among SC than VC animals, but sensitization was shown to be long-lasting in all vaccinated groups, whatever the administration route of the vaccine. VC vaccination with 10(9) CFU appeared to afford slightly greater protection than that with 10(8) CFU, and slightly lower protection than that induced by SC vaccination, but differences were not statistically significant. It is suggested that conjunctival vaccination with 10(9) CFU Rev. 1 would induce a good level of protection against Brucella melitensis infection and allow test and slaughter procedures as early as four months after vaccination.