Bovine Respiratory Syncytial Virus (BRSV) was first isolated in the United States in 1974 and recently has been identified as a major contributing agent in the Bovine Respiratory Disease (BRD) syndrome. It was named BRSV because this Pneumovirus invades the cell lining of the trachea and lungs and because it promotes the formation of large multinucleated cells called syncytial cells in the epithelium and interstitial spaces of the lung. BRSV appears to be widespread across the United States. In states where antibody prevalence testing has been done, 60% to 80% of the cattle tested are positive. Since research and information on BRSV are incomplete, we can only give a partial description of the disease syndrome produced by this virus.
An initial exposure to the virus usually produces: 1) a Mild Subclinical Infection which occurs approximately 5 days after stress and exposure. Within 2-10 days after recovery from this primary infection some animals will exhibit 2) a Severe Clinical Form of this disease, which if untreated will last 12-14 days and result in a high percentage of deaths. At any of these stages the course and severity of the disease can be aggravated by invasion of the weakened animal by other viral and bacterial pathogens.