Evaluation and application of an indirect ELISA for the detection of antibodies to bovine respiratory syncytial virus in milk, bulk milk, and serum

Department of Cattle, Sheep and Swine, National Veterinary Institute, Uppsala, Sweden.

An indirect enzyme-linked immunosorbent assay (ELISA) was developed at the National Veterinary Institute (NVI), Uppsala, to detect antibodies to bovine respiratory syncytial virus (BRSV) in serum and milk. For the evaluation of the NVI ELISA, field sera collected from cattle in England and Sweden were tested in parallel with an ELISA in use at the Central Veterinary Laboratory (CVL), Weybridge. The tests showed 96% agreement. The sensitivity and specificity of the NVI ELISA relative to the CVL ELISA were 94% and 100%, respectively. There was evidence that the difference in sensitivity between the 2 tests was due to the detection of both IgG and IgM class antibodies by the CVL ELISA, whereas the NVI ELISA was designed specifically to detect IgG1. Milk and serum samples from individual cows were tested by the NVI ELISA for presence of antibodies to BRSV. There was a good correlation between the ability to detect antibodies in serum and the ability to detect them in milk, although the antibody titer was generally lower in milk than in serum. Bulk milk samples were collected from farms with severe clinical symptoms of respiratory distress and from farms with no history of respiratory disease. There was a clear distinction between antibody levels in diseased and healthy herds. The NVI ELISA is a rapid and reliable test for detecting antibodies to BRSV in milk, bulk milk, and serum samples.