Histopathological Findings and Metagenomic Analysis of Esophageal Papillary Proliferation Identified in Laying Broiler Breeders

SIMPLE SUMMARY: This study describes the histopathological finding of mucosal papillary proliferation observed in the esophagus of chicken and attempts to determine its infectious etiology using metagenomics. Unlike squamous metaplasia of the esophageal mucosa due to vitamin A deficiency, the stratified squamous epithelial cells of the esophagus were completely replaced by increased numbers of ducts/ductules, lymphocytes, and connective tissue, and multiple hyperplasia of the esophageal gland was observed. As the result of the metagenomic analysis of esophagus samples from this chicken, no viral cause was identified; however, the contributing role of Bradyrhizobium sp. could not be excluded. In this study, we report the first histopathological examination of a rare case of an esophageal papillary lesion appearing as adenoma in a chicken and highlight the importance of histopathological results for a definitive diagnosis of such cases. ABSTRACT: White or pale-yellow nodules 2–7 mm in length were observed in the esophageal lumen in a number of laying broiler breeders with reduced laying rates. Metaplasia of the mucosal epithelial layer and mucous gland, as well as lymphocyte infiltration under the esophageal mucous gland and epithelial cell layer, were observed, which we found were caused by vitamin A deficiency. In one chicken, however, the stratified squamous epithelial cells of the esophagus were completely replaced by increased numbers of ducts/ductules, lymphocytes, and connective tissue, resulting in a papillary morphology. The ducts were surrounded by a fibrous stroma. Multiple hyperplasia of the esophageal gland was also observed and the esophageal glands were lined by a single layer of columnar cells, and a large number of lymphocytes were infiltrated into the submucosal layer. Based on the gross findings, this papillary proliferation was considered papilloma, but histopathologically, a mass composed of squamous epithelium was not observed. Therefore, the papillary lesion appeared as adenoma with squamous metaplasia of the esophageal gland and ectasia, or mucosal epithelial papillary hyperplasia, associated with chronic esophagitis. A metagenomic analysis of the esophagus samples from this chicken was performed to determine the infectious etiology. No viral cause was identified; however, a contributing role of Bradyrhizobium sp. could not be excluded. In this study, we report the first histopathological examination of a rare case of esophageal papillary proliferation in a chicken and highlight the importance of histopathological results for a definitive diagnosis of such cases.