Bacterial Pleuritis with Thickened Mesothelial Hyperplasia in a Young Beagle Dog

Abstract: A five-month-old male beagle dog suddenly became moribund. Bloody fluid accumulated in the thoracic and abdominal cavities, and soft yellow flecks were floating in the thoracic fluid. The mediastinum and pericardium became dark reddish with villous thickening. Other parietal and pulmonary pleurae were rough, and the organs adhered to each other. Histologically, most mediastinal pleura formed papillary projections covered by a single layer of mesothelial cells. Many macrophages and neutrophils infiltrated the submesothelial connective tissue. At the mediastinum adjacent to the pericardium, cuboidal mesothelial cells proliferated solidly and formed a thick surface stratum. The flecks consisted of gram-negative filamentous or small bacillary (coccoid) bacteria. In the right posterior lobe of the lung, neutrophilic infiltration and a large encapsulated abscess including a bacterial colony were present. We di-agnosed this case as “bacterial pleuritis with thickened mesothelial hyperplasia”. The cause of the pleuritis might be a chronic pleural infection spread via the lung abscess. (DOI: 10.1293/tox.26.313; J Toxicol Pathol 2013; 26: 313–317) Key words: bacterial pleuritis, mesothelial hyperplasia, beagle dog, Escherichia coli, Serratia odorifera, Acinetobacter lwoffii In dogs and cats, bacteria (such as Nocardia, Acti-nomyces, and Bacteroides) can cause pyogranulomatous pleuritis, and many species of bacteria can be present as ei-ther singular or mixed infection in pyothorax of dogs and cats1,2. It is well known that persistent serosal injury such a