An adult female American alligator (Alligator mississippiensis) had diffuse, yellow, granular serosal thickening at necropsy. Light microscopic examination of affected stomach, small intestine and spleen revealed a chronic proliferative serositis associated with 3 to 15 μm eosinophilic extracellular globules identified histochemically and morphologically as egg yolk. The intracoelomic egg yolk was considered to be the cause of the serosal reaction.
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