This document discusses bovine viral diarrhoea (BVD) virus, which exists in both cytopathic and non-cytopathic forms. The non-cytopathic form of BVD virus can cause congenital diseases in calves such as erosions in the Peyer's patches, congenital cerebellar hypoplasia, cataracts, retinal atrophy, microophthalmia, and optic neuritis.