D435 - Bovine respiratory syncytial virus

Bovine respiratory syncytial virus (BRSV) is an RNA virus classified as a pneumovirus in the paramyxovirus family. In additional to cattle, sheep and goats can also be infected by respiratory syncytial viruses. BRSV infections associated with respiratory disease occur predominantly in young beef and dairy cattle. Passively derived immunity does not appear to prevent Bovine respiratory syncytial virus infections but will reduce the severity of disease. Initial exposures to the virus are associated with severe respiratory disease; subsequent exposures result in mild to subclinical disease. BRSV appears to be an important virus in the bovine respiratory disease complex because of its frequency of occurrence, predilection for the lower respiratory tract, and its ability to predispose the respiratory tract to secondary bacterial infection. In outbreaks, morbidity tends to be high, and case fatality can be 0-20%.

A diagnosis of Bovine respiratory syncytial virus requires laboratory confirmation. BRSV has proved to be a difficult virus to detect by isolation procedures. Chances of isolation may improve by sampling animals that are in the incubation or acute phase of infection. Antigen detection enzyme immunoassay has been developed and is useful in detecting Bovine respiratory syncytial virus antigen and establishing an antemortem or postmortem diagnosis. Other procedures that have proved useful in detection of Bovine respiratory syncytial virus antigen are fluorescent antibody and immunoperoxidase staining. Paired serum samples can be used to establish a diagnosis of Bovine respiratory syncytial virus infection. However, the antibody titer of animals with well-developed clinical disease may be higher in the acute sample than in the sample taken 2-3 weeks later. This is because the antibody response often develops rapidly, and clinical signs follow virus infection by up to 7-10 days. Single serum samples showing high antibody titers from a number of animals in a respiratory outbreak may be useful in making a diagnosis if coupled with clinical signs. Calves that become infected with Bovine respiratory syncytial virus in the presence of passively derived antibody may not seroconvert. PCR-based test can be used as screening and confirmation testing for BRSV infection.