ULTRASTRUCTURAL STUDIES ON THE PATHOGENESIS OF SWINE DYSENTERY
Abstract
This investigation was designed to study and characterize the ultrastructural lesions of swine dysentery, and to evaluate the relationship between Treponema (T.) hyodysenteriae and colonic anaerobes in the induction of the disease. An attempt was also made to evaluate and compare the cytopathogenicity of T. hyodysenteriae and T. innocens on peritoneal macrophages of normal mice. Twelve pigs were inoculated orally with pure cultures of T. hyodysenteriae. Pigs were necropsied at different time intervals postinoculation; colonic and cecal specimens were collected and prepared for electron microscopy. The earliest colonic lesion detected by electron microscopy consisted of superficial vascular congestion and dilatation, edema of the lamina propria and intercellular separation of the epithelial cells at the crypt shoulders. This lesion progressed to epithelial cell necrosis and extrusion into the lumen and extravasation of red cells. Large numbers of spirochetes were present free, between, over and under necrotic epithelial cells whether in place or partially extruded. Spirochetal penetration of colonic enterocytes and intracytoplasmic multiplication were confirmed in this study. The spirochetes were found to invade the epithelial cells only from their lateral borders. The relationship between T. hyodysenteriae and the colonic anaerobes was not determined. One hundred twenty female mice (CF1 strain) were divided into 3 groups of 40. The first group was injected intraperitoneally with broth cultures of T. hyodysenteriae. The second group was injected with a combination of T. hyodysenteriae and Bacteroides vulgatus. The third group was injected with T. innocens. A peritoneal wash was collected at different time intervals postinjection, then prepared for and examined by electron microscopy. T. hyodysenteriae produced peritoneal macrophage aggregation, transient neutrophilia and cytolysis. Cytolysis was characterized by rarefaction of the cytoplasm, vesiculation of the endoplasmic reticulum, mild swelling of the mitochondria and disruption of the nuclear and cytoplasmic membranes. The combination of T. hyodysenteriae and B. vulgatus produced macrophage aggregation, marked neutrophil necrosis and delayed response of neutrophils. Peritoneal macrophages responded faster to T. hyodysenteriae, than to B. vulgatus at early postinjection intervals. T. innocens failed to produce cytotoxicity of peritoneal macrophages but did produce macrophage aggregation and transient neutrophilia.
Degree
Ph.D.
Subject Area
Animal diseases
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