High mortality rate associated with bovine respiratory syncytial virus (BRSV) infection in Belgian White Blue calves previously vaccinated with an inactivated BRSV vaccine

In a group of 60 Belgian White Blue calves less than 8 months old still hou sed in barns, a bovine respiratory syncytial virus (BRSV) outbreak was reve aled on the basis of a direct diagnosis (immunofluorescence and virus isola tion) performed on the lungs of dead animals, and the kinetics of BRSV neut ralizing antibodies. Clinical signs, macroscopical and microscopical pulmon ary lesions were also compatible with a BRSV infection. This outbreak is pe culiar because the 35 oldest calves (204 +/- 29 days old) had been vaccinat ed 3-4 months before with an inactivated BRSV vaccine and 30 % of these ani mals had died of respiratory distress. While they experienced a mild respir atory symptomatology, no death was recorded among the 25 youngest calves (6 9 +/- 29 days old) which had been left unvaccinated. Another peculiarity wa s found at the histological level where a massive infiltration of eosinophi ls was demonstrated in the pulmonary tissues of the dead animals. Together these data parallel the dramatic story described 30 years ago in children p reviously vaccinated with a formalin-inactivated human RSV (HRSV) vaccine u pon a natural HRSV challenge. This illustrates that an immunopathological p henomenon also takes place after BRSV vaccination in cattle.