Innocuousness of conjunctival vaccination with Brucella melitensis strain Rev.1 in pregnant Iranian fat-tailed ewes

Brucella melitensis strain Rev.1 is the most effective vaccine against brucellosis in sheep and goats. In Iran, mass vaccination is carried out all over the country in which adult animals are immunized by subcutaneous injection of reduced doses of the vaccine. However, due to antibody responses elicited by vaccination, concomitant implementation of test-andslaughter is impossible. To overcome the problem, vaccination through conjunctival route is recommended. In this study, serological responses of six pregnant Iranian fat-tailed ewes to conjunctival vaccination with standard doses of the vaccine were evaluated using modified Rose Bengal test, serum agglutination test and indirect ELISA. Besides, vaccine strain excretion in milk and vaginal discharges was also examined by microbiological culture of milk and vaginal swab samples taken one day post-parturition. Animals were vaccinated during the second half of gestation. As the results, antibody titers of five (83.3%) ewes decreased to the levels not detectable by the tests within three months after vaccination. No vaccine-induced abortions occurred and vaccinated ewes delivered healthy lambs 50.33±15.56 (mean ± standard deviation) days post-vaccination. Vaccine strain was not isolated from milk and vaginal swab samples. Generally, our study shows full doses of B. melitensis strain Rev.1 can be used conjunctively to vaccinate pregnant Iranian sheep during late pregnancy without abortifacient effects, prolonged antibody responses and vaccine strain excretion in milk and vaginal discharges. Nevertheless, further studies are required to determine safety and immunogenicity of the vaccine in field conditions.