Development of an enzyme-linked immunosorbent assay for detection of serum antibodies to haemorrhagic septicaemia

An indirect enzyme-linked immunosorbent assay (ELISA) was developed using a heat-stable extract of Pasteurella multocida serotype 6:B to detect antibodies to haemorrhagic septicaemia (HS) in serum from cattle and buffaloes. The sera were tested at 1:400 dilution and the optical density was compared with a standard curve. The results were expressed in ELISA units. There was 91% agreement when the ELISA results were compared with the indirect haemagglutination test using field samples. The ELISA was used to detect specific serum antibodies in buffaloes after vaccination with an HS-oil adjuvant vaccine. The first three months after vaccination showed a gradual rise in HS antibody concentration which was followed by a marked increase over the next 14 days when a second vaccination was given at 3 months. Nine months after the initial vaccination the animals were challenged intranasally with 109 colony-forming units of P. multocida. All animals survived. This suggested that the ELISA is capable of detecting antibodies responsible for protection. Colostral derived antibodies to HS were also detected by ELISA in newborn buffalo calves. The antibody concentration increased markedly within 24 hours of colostral consumption but declined within 28 days of birth. The immune response to P. multocida in rabbits was also measured by ELISA. A 50-fold increase in the antibody concentration occurred within 36 days of vaccination. The ELISA developed in this study proved to be useful for measuring antibodies to P. multocida in cattle and buffaloes and will assist in monitoring antibody responses to vaccination against HS. (author). 25 refs, 4 figs, 1 tab