EQUINE BACTERIAL PLEUROPNEUMONIA .1. EPIDEMIOLOGY, PATHOPHYSIOLOGY, AND BACTERIAL ISOLATES

Bacterial pleuropneumonia is a severe respiratory disorder that causes sizable economic losses to the equine industry. The disease involves colonization of the lung by pathogenic bacteria, development of pneumo nia and/or pulmonary abscess formation, and subsequent extension to th e visceral pleura and pleural space; the accumulation of parapneumonic effusion results. In the United States, pleuropneumonia is the most c ommon cause of pleural effusion in horses. Racehorses are apparently a t greater risk of developing pleuropneumonia. Transport and strenuous exercise are evidently major risk factors. Parapneumonic effusion deve lops secondary to increased capillary permeability of the visceral lun g and decreased drainage of the pleural fluid via lymphatics. Parapneu monic effusion evolves in three stages: exudative, fibrinopurulent, an d organizational. Polymicrobic and mixed aerobic-anaerobic isolates ar e common.