A chronic pneumonia of sheep caused by a lentivirus, which also causes visna when it invades the brain of sheep. In maedi the characteristic features are a prolonged incubation period of more than 2 years, a progressive pneumonia which lasts for about 6 months, and, at the inevitable death, an abnormally high density and heaviness of the lungs. Called also maedi–visna, Graff–Reinert disease, la bouhite, ovine progressive pneumonia and lymphoid interstitial pneumonia.

Saunders Comprehensive Veterinary Dictionary 3rd Edition. Copyright © 2007 by D.C. Blood, V.P. Studdert and C.C. Gay, Elsevier. All rights reserved.