Pathology of gastrointestinal helminthiasis in the brown pelican (Pelecanus occidentalis).

Lesions caused by experimentally produced mixed infections (two flukes, Phagicola longa and Mesostephanus appendiculatoides, and an ascarid, Contracaecum sp.) were studied in 40 brown pelicans. The flukes occurred throughout the intestines and caused mild villus atrophy, lengthening of the crypts, increased goblet cell population, and lymphoplasmacytic infiltration. Contracaecum caused small ulcers where they attached to the esophagus and proventriculus. Microscopically, these ulcers had an eosinophilic, hyaline lining surrounded by focal necrosis, cellular infiltration, and fibrosis. Changes in several biochemical constituents of the blood were seen. These gastrointestinal parasitisms had low virulence, and they probably play a secondary role as a factor influencing population fluctuations in brown pelicans.