Microscopical aspects of the ileal specimen and parasitic stools examination of case No. 1. A. Longitudinal section of a mesenteric artery with an A. costaricensis adult inside arterioles (dart) (HES, 100x). B. Cross section of intra-mesenteric arterial adult nematodes (darts) with an eosinophilic inflammatory infiltrate in the surrounding tissues. One harbors a reproductive tube (RT) (HES, 100x). C. Impaired embryonated egg of nematode (maybe A. costaricensis) (dart) measuring 80 × 35 μm (MIF, 200x) found in stools collected four days after abdominal surgery.