title: Progressive pneumonia in sheep: incidence of natural infection and establishment of clean flocks.
mesh_terms: D000367:Age Factors; D000818:Animals; D000914:Antibodies, Viral / Q000096:biosynthesis; D005260:Female; D009658:North Dakota; D011021:Pneumonia, Progressive Interstitial, of Sheep / Q000453:epidemiology* / Q000276:immunology / Q000517:prevention & control; D012756:Sheep; D014790:Visna-maedi virus / Q000276:immunology
chemical_list: D000914:Antibodies, Viral