Serological response in cattle and sheep following infection or vaccination with bluetongue virus.

Data from various experimental and field studies were compiled and analysed to evaluate the serological response in sheep and cattle against different bluetongue (BT) virus (BTV) vaccine combinations (Onderstepoort Biological Products, South Africa); the accuracy of diagnostic procedures commonly used for detecting BTV antibodies was also assessed. Using the competitive enzyme-linked immunosorbent assay (c-ELISA) (IZSA&M, Teramo, Italy) and the virus neutralisation (VN) test, antibody responses were evaluated under the following vaccination regimes: monovalent modified-live vaccine against BTV-2 in cattle and sheep, monovalent modified-live vaccine against BTV-9 in sheep, and bivalent modified-live vaccine against BTV-2 and BTV-9 in cattle and sheep. The data were compared to serological results observed in cattle and sheep infected with Italian field strains of BTV-2 or BTV-9. The c-ELISA consistently detected antibodies earlier than the VN test in both livestock species and against all BTV serotypes. The highest and most rapid antibody responses were observed in sheep infected in the field. In cattle and in sheep, high VN titres were detected using monovalent vaccines, while bivalent vaccines initiated lower antibody titres that developed more slowly.