Porcine Abortion Caused by Actinomyces suis

Three abortions occurred in a herd of 400 mixed breed pigs within 1 month. In one case, two piglets (3 weeks premature) and a serum sample from the dam were submitted to our laboratory. The herd had been vaccinated for leptospirosis, parvovirus, and pseudorabies. Postmortem examination revealed mild generalized subcutaneous edema, ascites, and hydrothorax, with some fibrin in the pleural fluids of both fetuses. Histopathologically, there was diffuse, severe, pyogranulomatous bronchopneumonia. Bronchiolar and alveolar spaces were filled with large foamy macrophages, neutrophils, and numerous giant cells. Large numbers of filamentous to rod-shaped, weakly gram-positive bacteria were in giant cells and free in inflammatory exudates (Figs. 1, 2). Organisms stained poorly with periodic acid-Schiff (PAS) but strongly with Warthin-Starry silver stains. Based on characteristics of the organism, Bacillus piliformis was included as a possible cause for the lesions. Formalin-fixed tissues did not stain on indirect immunofluorescence tests for antigens of Bacillus