Antibody dynamics in BRSV-infected Danish dairy herds as determined by isotype-specific immunoglobulins

Using specific ELISAs, antibody levels of four different isotypes to bovine respiratory syncytial virus (BRSV) were determined in calves, following ex perimental BRSV infection. Most calves experienced an increase in the speci fic IgM and IgG1 titres about 6-10 days after infection with BRSV. The IgM titre was transient showing positive titres for only 5-10 days, while speci fic IgG1 was present for a longer time. IgA was detected concomitantly with IgM but at a lower level. Production of IgG2 anti-BRSV antibodies was dete cted from 3 weeks after infection. In two closed herds, repeated blood samplings were performed on young stock to analyse maternal immunity. The passively transferred antibodies were ma inly of the IgG1 isotype and the half-life of IgG1 to BRSV was estimated to be 26.6 days. One of the herds had an outbreak of enzootic pneumonia, diag nosed to be caused by BRSV. Furthermore, another herd with acute BRSV was f ollowed by weekly blood samples in six calves; in both herds IgM and IgG1 w as detected shortly after the appearance of clinical signs. Serum samples from 50 Danish dairy herds (453 samples) were tested for immu noglobulins of the isotypes IgG1, IgG2 and IgM. The presence of antibodies to BRSV was widespread and more than 54% of the samples had BRSV antibodies of both the IgG1 and IgG2 isotypes indicating a high herd prevalence to BR SV. Test samples from two herds out of 50 were free from all isotypes to BR SV. (C) 2000 Elsevier Science B.V. All rights reserved.