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Medical Definition of Visna-maedi virus
1. A species of lentivirus, subgenus ovine-caprine lentiviruses (lentiviruses, ovine-caprine), that can cause chronic pneumonia (maedi), mastitis, arthritis, and encephalomyelitis (visna) in sheep. Maedi is a progressive pneumonia of sheep which is similar to but not the same as jaagsiekte (pulmonary adenomatosis, ovine). Visna is a demyelinating leukoencephalomyelitis of sheep which is similar to but not the same as scrapie. (12 Dec 1998)