Use of milk samples and monoclonal antibodies directed against BLV-p24 to identify cattle infected with bovine leukemia virus (BLV).

An indirect double-antibody sandwich (IDAS) enzyme-linked immunosorbent assay (ELISA) using milk samples was developed to identify cows infected with bovine leukemia virus (BLV). Two monoclonal antibodies (McAbs) were used. One, which was directed against BLV core protein p24, was used to coat ELISA plates; the other was used to prepare a horseradish peroxidase (HRP) conjugate directed against bovine immunoglobulin. The IDAS-ELISA detected antibodies directed against BLV-p24 in 97% of the milk samples collected from known seropositive cows identified by the agar gel precipitation test (AGTP). Even when milk samples were diluted 1:50, 93% of the seropositive cows were identified. Only 0.43% of the 4000 milk samples collected in The Netherlands reacted nonspecifically. Nonspecific binding disappeared, however, when these samples were diluted 50 times in BLV-negative milk. In a comparative evaluation of BLV test-kits in various European laboratories, our IDAS-ELISA using McAb directed against p24 was one of the most sensitive.