Infection of the colon of the rhesus monkey by spiral-shaped organisms.

Intestinal spirochetosis, an infection of the mucosa by spiral-shaped organisms, was studied in clinically normal rhesus monkeys (Macaca mulatta) by histology, transmission and scanning electron microscopy. The incidence of intestinal spirochetosis was 42% in 221 monkeys. Spiral organisms stained with hematoxylin and eosin (HE) appeared as a broad basophilic haze on the colonic surface and were strongly positive by the Warthin-Starry stain. Spiral-shaped bacteria include two structurally different organisms: spirochetes and flagellated microbes. They intimately populated the brush border of the surface of the epithelium of the large intestine. They were absent in the crypts and in the small intestine. Infection by spirochetes produced no alteration of cytocomponents of the underlying host structures. Spirochetes and flagellates infrequently penetrated beyond the brush border into the epithelial cytoplasm and also into the lamina propria. Even in cases where invasion was documented, no inflammatory response was found.