[Suspicion of visna in a sheep from Graubünden Canton]

A lentivirus belonging to the group of retroviridae causes a chronic progressive interstitial pneumopathy (maedi) or a demyelinating encephalo-myelitis (visna) in sheep and goats. Pulmonary lesions of maedi as well as sero-positive, clinically healthy animals can be observed in Switzerland; visna, which even in countries with endemic infection does not occur frequently, is extremely rare. The head and cervical spine of an ewe with severe nervous troubles suspected of scrapie were submitted for postmortem examination. We found a demyelinating myelitis resembling visna. Immunocytochemical staining (PAP) to demonstrate the presence of the virus in paraffin sections was negative, but several animals of the flock proved to be seropositive for maedi/visna virus, which supports the histological diagnosis. Although there is no risk of an epidemic outbreak of maedi/visna in Switzerland, modes of transmission, eradication programmes and prophylactic measures successfully employed in countries with endemic maedi/visna are discussed.