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

Abstract

Using specific ELISAs, antibody levels of four different isotypes to bovine respiratory syncytial virus (BRSV) were determined in calves, following experimental BRSV infection. Most calves experienced an increase in the specific 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 specific 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 detected 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 mainly 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, diagnosed to be caused by BRSV. Furthermore, another herd with acute BRSV was followed by weekly blood samples in six calves; in both herds IgM and IgG1 was detected shortly after the appearance of clinical signs. Serum samples from 50 Danish dairy herds (453 samples) were tested for immunoglobulins 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 BRSV. Test samples from two herds out of 50 were free from all isotypes to BRSV.

Fig. 1

Body temperature and kinetics of antibody activity to BRSV in three colostrumfed, two- to three-month old calves after experimental primary infection with BRSV. Nasal swabs were taken daily (except day 6 and 7); detection of BRSV-antigen is shown as “V”.

Fig. 2

Metabolism of maternal antibody activity in calves analysed during the first half year of life. Results are shown as the mean titre and S.E.M. The calves in herd A (N=13), had no signs of pneumonia during the intensive observation period until February. In herd B (N=11) an epizootic was present in the end of December. Antibodies to BRSV were analysed by isotype-specific ELISAs, antibodies to bovine corona virus were not subtyped. *Only sera from 5 calves were analysed. Symbols: (--•--) Neutralisation titers; (--▿--) lgM; (--○--) lgG1; (--×--) lgG2; (--□--) lgA; (-■ --) corona. Antibody titres to corona virus are 10 times the value on the ELISA axis.