BORDER DISEASE OF SHEEP AND GOATS

Border disease (BD) is a congenital virus disease of sheep and goats f irst reported in 1959 from the border region of England and Wales. ED virus (BDV) is a pestivirus in the genus Flaviviridae and is closely r elated to classical swine fever virus and bovine virus diarrhoea virus (BVDV). Nearly all isolates of BDV are non-cytopathogenic (ncp) in ce ll culture. There are no defined serotypes but pestiviruses isolated f rom sheep exhibit considerable antigenic diversity and three distinct antigenic groups have been identified. Distribution of the virus is wo rldwide. Prevalence rates vary in sheep from 5 to 50 % between countri es and from region-to-region within countries. The disease in goats is rare and characterized by abortion. Clinical signs in sheep include b arren ewes, abortions, stillbirths and the birth of small weak lambs. Affected lambs can show tremor, abnormal body conformation and hairy f leeces (so-called 'hairy-shaker' or 'fuzzy' lambs). Vertical transmiss ion plays an important role in the epidemiology of the disease. Infect ion of fetuses can result in the birth of persistently infected (PI) l ambs. These PI lambs are viraemic, antibody negative and constantly ex crete virus. The virus spreads from sheep to sheep with PI animals bei ng the most potent source of infection. Apparently healthy PI sheep re sulting from congenital infection can be identified by direct detectio n of viral antigen or viral RNA in leukocytes or by isolation of ncp v irus from blood or serum in laboratory cell cultures. Isolation of vir us is unreliable in lambs younger than 2 months old that have received colostral antibody. The isolation of virus from tissues of aborted or stillborn lambs is difficult but tissues from PI sheep contain easily detectable levels of virus. To detect the growth of virus in cell cul tures it is essential to use an immune-labelling method. Acute infecti on is usually subclinical and viraemia is transient and difficult to d etect. Sheep may also be infected following close contact with cattle excreting the closely related BVDV. (C) Inra/Elsevier, Paris.