FIG 7.

Lung tissue from calves in study 2 treated with GS1 or placebo. Lung tissue from calf 1-2 (calf 2 from group 1) from study group 1 (GS1 treatment at 24 h postinfection) showed minimal multifocal multilobular atelectasis (<1% of lung mass) and mild bilateral neutrophilic histiocytic bronchopneumonia. Mycoplasma bovis was isolated from the tissue, but bRSV antigen was not detected by immunostaining. Lung tissue from calf 2-6 (calf 6 from group 2) from study group 2 (GS1 treatment at 72 h postinfection) showed minimal focal multilobular consolidation in the right middle lobe (<1% of lung mass) with regional focal multilobular atelectasis with minimal histiocytic neutrophilic bronchopneumonia. Mycoplasma bovis was isolated from lung tissue but was negative for bRSV by immune staining. Lung tissue from calf 3-3 (calf 3 from group 3) from study group 3 (placebo-treated animal) showed severe bilateral anteroventral pulmonary consolidation (45 to 50% of the lung mass). The affected lung lobes showed extensive multilobular areas of neutrophilic bronchopneumonia with multifocal necrosuppurative bronchiolitis and focal necrosis. Arcanobacterium pyogenes and Mycoplasma bovis were isolated from lung tissue, but bRSV was not detected by immune staining. A description of the histopathology results for individual animals is shown in Table S4 in the supplemental material.