Assessment of serological response of young and adult sheep to conjunctival vaccination with Rev-1 vaccine by fluorescence polarization assay (FPA) and other serological tests for B. melitensis

The serological response of young and adult sheep vaccinated conjunctivally with Rev-1 vaccine was assessed by fluorescence polarization assay (FPA), Rose Bengal test (RBT), complement fixation test (CFT), modified Rose Bengal test (m-RBT), indirect ELISA (i-ELISA) and competitive ELISA (c-ELISA), at different post vaccination intervals. One hundred and thirty six adult sheep and 64 lambs were used in the study. The vaccinated animals were bled prior to vaccination (0 day) and thereafter at 21st, 42nd, 35th, 63rd, 91st, 125th, 159th, and 223rd and 330th day post vaccination. The majority of animals (young and adult) showed positive reaction by FPA, RBT, CFT, m-RBT and c-ELISA 21 days post vaccination, whereas by i-ELISA at 42 days. All tests perform equal when animals vaccinated as young are tested 125 days (4 months) post vaccination. In case of animals vaccinated at adulthood, FPA, RBT, CFT and c-ELISA perform equal if the animals are tested 223 days (≈8 months) post vaccination. I-ELISA and m-RBT show low specificity if ewes vaccinated at adulthood are tested 330 days (11 months) post vaccination. If control of brucellosis in sheep is based on conjunctivally vaccination of lambs with Rev-1, the vaccinated animals can be tested by any test used for diagnosis of B.melitensis infection accurately at least 4 months post vaccination. If brucellosis control is based on mass vaccination the use of m-RBT and i-ELISA is not recommended for testing adult animals at least for 330 days (11 months) post vaccination due to tests low specificity. Further research is needed so the appropriate cut-offs to be established for FPA, c-ELISA or i-ELISA to become valuable tools for the eradication of Brucella spp. infection in small ruminants in areas where vaccination is practiced.