Parainfluenza-3 is a Paramyxovirus belonging to the same family as BRSV. PI3 virus has been isolated, identified and studied in relation to Bovine Respiratory Disease (BRD) syndrome. PI3 virus is commonly isolated from animals suffering from BRD, although it appears to be more of a contributing agent rather than a primary pathogen. By itself PI3 virus produces a rather benign infection of the lung. PI3 antibodies have been detected in approximately 90% of the cattle tested in the United States. It most commonly invades the lungs causing a fibrinous pleuritis and pneumonia.