Bovine parainfluenza-3 virus.

Bovine parainfluenza-3 virus (bPI(3)V) is a long-recognized, currently underappreciated, endemic infection in cattle populations. Clinical disease is most common in calves with poor passive transfer or decayed maternal antibodies. It is usually mild, consisting of fever, nasal discharge, and dry cough. Caused at least partly by local immunosuppressive effects, bPI(3)V infection is often complicated by coinfection with other respiratory viruses and bacteria, and is therefore an important component of enzootic pneumonia in calves and bovine respiratory disease complex in feedlot cattle. Active infection can be diagnosed by virus isolation from nasal swabs, or IF testing on smears made from nasal swabs. Timing of sampling is critical in obtaining definitive diagnostic test results. Parenteral and intranasal modified live vaccine combination vaccines are available. Priming early in calfhood with intranasal vaccine, followed by boosting with parenteral vaccine, may be the best immunoprophylactic approach.