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.

The effect of selected anthelmintics (albendazole, fenbendazole, piperazine dihydrochloride and clorsulon) against three major helminths (Contracaecum multipapillatum, Mesostephanus appendiculatoides, and Phagicola longus) were studied in 29 brown pelicans (Pelecanus occidentalis). Albendazole and fenbendazole were highly effective against all three parasites. Clorsulon had moderate effect against M. appendiculatoides and poor effect against C. multipapillatum and P. longus. Piperazine dihydrochloride had no effect against these helminths.

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