Bovine viral diarrhoea in cattle and border disease in sheep are caused by infection with the pestiviruses bovine viral diarrhoea virus (BVDV) and border disease virus (BDV), respectively, although either virus is capable of infecting both species with comparable outcomes.1,2 In sheep, acute (or transient) BDV infection is generally mild and leads to seroconversion and clearance of the virus, although some strains with increased pathogenicity have been observed.2–4 The main effect of border disease is seen when pregnant ewes are infected, leading to infertility, abortion, stillbirth and birth of small and weak lambs. Surviving lambs may show nervous signs and changes to the fleece, giving rise to the term ‘hairy shakers’ for infected lambs (Fig 1), although some infected lambs may appear normal. Such lambs are persistently infected (PI) with BDV and, like calves persistently infected with BVDV, they are born tolerant of the virus. They have no immune response to infection and continue to shed virus throughout their lives, presenting a risk of infection through both direct and indirect contacts. FIG 1: A group of border disease persistently infected lambs, born following infection of ewes during pregnancy. Note the fine appearance of the fleece when seen in profile, characteristic of the ‘hairy shaker’ phenotype. PI lambs do not develop virus-specific antibodies, so detection of infection is only possible by ELISA to detect viral antigen or reverse transcription-PCR to detect viral RNA. Current antibody tests do not distinguish between BVDV and BDV infection as the viruses are antigenically similar but antibodies against pestiviruses can be differentiated using virus neutralisation assays that include the virus species of interest. The virus causing the infection will be neutralised with the highest titre.2 The economic impact of BVDV has led to the introduction of BVDV eradication schemes in various countries across western Europe.5 In Scandinavia and Switzerland few …