Prevalence of ovine progressive pneumonia in a sampling of cull sheep from western and midwestern United States.

Ovine progressive pneumonia was found to be prevalent in many major sheep-producing areas in the United States. The incidence was determined in a sampling of cull sheep (5 to 10 years of age) at slaughter. Diagnostic criteria were based on finding viral-specific immunoglobulins, virus, or lesions. Each method indicated a high incidence in samplings from midwestern and northwestern states and a relatively low incidence in the sampling from southwestern states. Of those sheep examined, precipitating immuno-globulin to the causal virus was seen in 1.0% to 67.5%, virus was isolated from the lungs of 0% to 46.2%, and lymphoid hyperplasia was seen in the lungs of 0% to 38.5%. The most common lesions in the lungs (from which virus was isolated) were multiple lymphoid nodules and increased fibromuscular tissue.