SEROLOGICAL INDICATION FOR PERSISTENCE OF BOVINE RESPIRATORY SYNCYTIAL VIRUS IN CATTLE AND ATTEMPTS TO DETECT THE VIRUS

To identify putative persistent bovine respiratory syncytial virus (BR SV) infections in cattle, seven cattle that had experienced BRSV infec tions were treated with corticosteroids for two periods of 5 days. Dur ing the 5-day periods and the 3 weeks after treatment, attempts were m ade to isolate BRSV from lung lavage fluid and nasal swab specimens. F luorescent antibody tests were used to detect BRSV antigen in lung lav age cells. A BRSV specific polymerase chain reaction (PCR) assay was d eveloped, and was performed on lung lavage samples of all seven cattle as well as on various tissues of five of the cattle. In addition, nas al swabs of 74 over-one-year-old cattle, in a closed dairy herd were a lso assayed by PCR. The virus or its RNA was not detected in putative carriers, by any of the methods used, whereas all positive controls we re positive. After corticosteroid treatment, three of the seven cattle showed a fourfold rise in antibody titre, suggesting induction of vir us replication. BRSV-seronegative sentinel calves, that were housed to gether with each corticosteroid-treated animal, did not develop antibo dies to BRSV indicating that BRSV was not shed by corticosteroid-treat ed cattle, or was shed at a very low level. In addition BRSV was not d etected in seropositive cattle in a closed farm in summer. Although we consider the rises in antibody titres against BRSV an indication for persistence of BRSV in cattle, BRSV or its RNA was not detected in inf ected cattle.