Vaccine effect on virus load, clinical disease and lung pathology after BRSV challenge.

aConventional colostrum-fed calves were immunized with either ΔSHrBRSV, SUMont, SUAbis or adjuvant alone, as indicated in the table. All animals were immunized on post-infection day (PID) −34, and all animals except those immunized with ΔSHrBRSV were immunized again on PID −14, and all were challenged with BRSV on PID 0, as indicated in Figure 1.bAge at first vaccination (weeks).cSerum titer of BRSV-specific maternal antibodies (MDA) before first vaccination (PID −36) as determined ELISA.dAccumulated viral-shed in nasal secretions and virus RNA detected in 1 ml of bronchoalveolar lavage (BAL) collected as indicated in figure 1. Samples were analyzed using BRSV-F real-time PCR after total RNA extraction. The unit TCID50 equivalent is determined by including standard dilution series of virus with a known TCID50 in the real-time PCR analysis.eVirus isolated from post-mortem BAL cell samples, after inoculation of bovine turbinate epithelium cells in 25 cm2 flasks in three consecutive passages. In any of the three passages, cell cultures with evident cytopathic effects within seven days of culture were determined to be positive for BRSV in passage one (+P1), two (+P2) or three (+P3). Samples that were negative after three passages are noted as negative (–).fAccumulated clinical score, calculated as the area under the curve of daily clinical scores, in turn determined by clinical examination.gExtent of lung lesions were determined post mortem and are presented as a percentage of lesioned lung tissue per calf.†Calf c5 was euthanized before challenge due to traumatic injury.