Diagnosis of bovine respiratory syncytial virus infections improved by virus detection in lung lavage samples.

The potential of lung lavage to diagnose and study infections with bovine respiratory syncytial virus (BRSV) was investigated. The technique was simple to perform under field conditions, and even in calves with respiratory tract disease, serious drawbacks were not observed. In 9 epizootics of respiratory tract disease, BRSV infection was diagnosed in 1 or more calves. The BRSV was detected from a total of 21 of 32 calves by immunofluorescence in cells recovered from lavage fluids, and the virus was recovered by cell culture from 17 of these. In the 4 remaining calves, infectious bovine rhinotracheitis virus or parainfluenza type 3 virus was isolated. In calves with high levels of maternally derived antibodies, direct demonstration of the virus was found to be essential for making a diagnosis of BRSV. In 3 of the 9 epizootics, the majority of 4- to 8-month-old calves had a significant increase in antibody concentration against BRSV, whereas only a few 1- to 2-month-old calves present during the other 6 epizootics did so. However, at least in 4 of the 6 herds with younger calves, direct detection of the virus in 2 or more calves indicated that BRSV was involved in the epizootic. Cytologic examination of wash fluids from BRSV-infected animals identified an increased neutrophil/large mononuclear cell ratio. Occasionally, bronchiolar casts and syncytial giant cells with inclusion bodies were seen. In lung lavage fluids of 4 experimentally infected specific-pathogen-free calves, BRSV-containing cells were detected by immunofluorescence for 12 to 18 days after inoculation.