LENTIVIRUS-INDUCED INTERSTITIAL LUNG-DISEASE - PULMONARY PATHOLOGY INSHEEP NATURALLY INFECTED BY THE VISNA-MAEDI VIRUS

Visna-maedi virus is a lentivirus that causes a chronic disease in she ep affecting, among other organs, the lungs. Interstitial pneumonitis is similar to that in man associated with the infection by the human i mmunodeficiency virus type-1. We have compared the pathological featur es of lungs of sheep naturally infected with visna-maedi virus with th e results obtained from bronchoalveolar lavage and virus isolation. Se mi-quantitative grading of the lesions was performed on 147 sheep lung s obtained from the slaughterhouse. Seventy-seven were macroscopically and histologically normal, 39 had typical lesions of interstitial lun g disease (maedi), and 13 had minor lesions of the same type. Eighteen of the affected lungs were heavily infested with parasites. Of these parasite-infected lungs, 9 showed typical maedi lesions and 4 showed m inor lesions; parasite infection had no obvious effect on the developm ent of maedi. In keeping with pathological findings, bronchoalveolar r avage disclosed an alveolitis process in the maedi lungs with increase d macrophage, lymphocyte and neutrophil numbers. Cytopathic virus was detected from alveolar macrophage coculture with fibroblasts more ofte n from maedi lungs (10/12) than from normal lungs (9/39). Electron mic roscopy of bronchalveolar lavage cocultures revealed typical lentivira l particles. Animals with minor lesions may be at an early stage of th e disease.