BVDV can infect cattle at any age. It is usually a mild disease with recovery by 10 days. However, it can play a key role in calf respiratory disease and enteritis. By causing immunosuppression, the virus facilitates other pathogens to produce more severe disease e.g. IBR, RSV & Salmonella. In some outbreaks, BVDV can cause more serious disease with diarrhoea, anorexia and agalactia. The variation in virulence has not been explained. A recent syndrome, seen in the USA, is described below.