DYNAMICS OF BOVINE RESPIRATORY SYNCYTIAL VIRUS-INFECTIONS - A LONGITUDINAL EPIDEMIOLOGIC-STUDY IN DAIRY HERDS

To study the epidemiology of respiratory syncytial virus (RSV) infections during the year, the incidences of primary infections and reinfections were monitored by titrating antibodies to bovine RSV (BRSV) in cattle above 2 months of age in 6 dairy herds in the Netherlands. From August 1990 until September 1991, 884 cattle were sampled at one-month intervals. A total of 155 cattle, most under two years of age, had a primary antibody response. Antibody rises were found in 259 cattle of all ages. The highest incidences of BRSV infections were found in one period either in autumn or winter. In other seasons, primary infections were rare, whereas reinfections were not uncommon. In 5 out of the 6 herds, two seronegative sentinel calves were introduced at the end of the winter and none developed specific antibodies before the next winter. The observations strongly suggest that, in spite of regular reinfections, BRSV circulates during spring or summer at a very low level or not at all. Persistent BRSV infection in a number of cows might be a means for the virus to survive during summer, but a steady rate of reinfection of seropositive cows throughout the year at a low level might also maintain a reservoir of infectious virus. This study adds to the knowledge of frequency and timings of primary infections and reinfections of BRSV and it might contribute to the study of these issues of human RSV.