Colon, Incidental spirochetosis

Intestinal spirochetosis is caused by Brachyspira aalborgi and Brachyspira pilosicoli. It is generally an asymptomatic infection and may be found incidentally, as in this case. It is more common in developing countries, those who are HIV positive, and men.

Histologically, it is seen as distinctive basophilic, fringe like, end-on-end attachment of densely packed filamentous spirochetes (Brachyspira aalborgi or B. Pilosicoli) on the surface of the large intestine or appendix. Warthin-Starry stain can be used to confirm diagnosis.