Immunopathological responses and kinetics of Brucella melitensis Rev 1 infection after subcutaneous or conjunctival vaccination in rams

Summary The innocuousness of the Brucella melitensis Rev 1 live attenuated vaccine strain has never been fully assessed in rams. The immunopatholological responses and the kinetics and distribution of the infection induced by this strain were determined after subcutaneous or conjunctival vaccination in both young (3–4 months old) and adult (12 months old) rams. At regular intervals after vaccination the animals were bled for serological studies, and slaughtered for both pathological and bacteriological examinations. The serological response after conjunctival inoculation was of lower intensity and duration than that induced subcutaneously, being the differences more evident in young rams. No genital lesions were produced and genital organs and accessory sexual glands were never found infected, being Rev 1 infection restricted to lymph nodes and spleen. Immunostained Rev 1 bacteria were located intracellularly in plasmablasts, dendritic follicular cells and macrophages in the target lymph nodes, in which cellular hyperplasia was the dominant pathological response. Subcutaneous vaccination induced a generalized infection by 2 weeks after vaccination, being then restricted to the prescapular target lymph node. Infection after conjunctival vaccination was less generalized, being restricted essentially to the cranial lymph nodes. Rev 1 infection was fully cleared by 3 months after vaccination in all animals. These results confirm the innocuousness of B. melitensis Rev 1 vaccine in rams.