Impact of Nematodes on the Gastric Mucosa of the American Alligator (Alligator mississippiensis)

Abstract

| The intestinal tract represents an ideal habitat for a large number of parasites, as compared to stomach’s acidic environment. The American alligator ( Alligator mississippiensis , Daudin) has “typical” vertebrate gastric pits and glands in the stomach mucosa, with a corresponding acidic gastric environment. Crocodylians have a remarkably effective immune system, which enables them to combat microbial infections and allows relatively quick wound healing. We sought to explore how the alligator’s immune system responded to parasites, rather than microbial, challenges. We examined the stomachs of 14 sub-adults, wild-caught, American alligators from the coastal region of Louisiana, and found that four (~29%) were infected with enteric helminthes. Two different nematodes were found: Dujardinascaris waltoni (Nematoda: Heterocheilidae) was found loose among the stomach contents, whereas Ortleppascaris antipini (Nematoda: Ascaridoidea) was associated with multifocal lesions in the gastric mucosa. These lesions were roughly 4 mm in diameter, housed multiple parasites, and formed an elevated node of mucosa and nematodes. As the parasites invaded the gastric mucosa, they induced a granulomatous inflammation near the lesion; the site of worm attachment was associated with a marked eosinophilic necrosis. This cellular response produced a penumbra around the invasive nodule that was clearly visible under light and electron microscopy. Embedded worms were surrounded by an eosinophilic exudation, presumably representing proliferating host mucosal tissue, which formed the elevated nodule. Mucosal burrows of the nematodes led to a loss of the gastric pits in the infected zone and a presumed decrease in digestive efficiency of the host alligator.