An outbreak of visceral coligranuloma in a backyard chicken flock

Abstract

A rare outbreak of coligranuloma in a backyard chicken flock at the age of 9 weeks occurred on March 2012, in Kermanshah Province, Iran. The flock was raised in poor hygienic conditions. The birds were kept indoor at night on deep wet litter and had access to a small range during the day. They had access to a pond with stagnant water. The affected birds were dull, depressed, and anorectic. The mortality was about 20 birds per 24 h. This mortality rate lasted for 2 weeks. Total mortality reached 20 %. Out of 1,120 chickens that survived and slaughtered at the age of 11 weeks, 571 (51 %) were condemned due to visceral granuloma. At necropsy, affected chickens were poorly fleshed and showed airsaculitis and granulomas. They had masses of whitish-gray nodules on the mesenteries and serosal surface of the intestines. The representative nodules were sectioned and stained with hematoxylin and eosin. Some sections of lesions were stained with periodic acid-Schiff (PAS) and Ziel–Nielsen (ZN) methods. Lesions from affected birds were routinely cultured on blood agar and MacConkey’s agar. At light microscopy, the granulomas were often characterized by accumulations of eosinophilic necrotic debris surrounded by epithelioid cells and multinucleated giant cells. No mycotic forms were seen in slides with PAS stain and no acid-fast organisms were seen in ZN-stained sections. Bacteriological cultures of lesions yielded a non-hemolytic Escherichia coli. Based on gross lesions, histological findings, and results of bacteriological cultures, the condition was confirmed as coligranuloma.