Histopathological study of avian tuberculosis in naturally infected domestic pigeons with Mycobacterium avium subsp. avium

The aim of this study was to investigate the histopathology of avian tuberculosis in naturally infected domestic pigeons (Columba livia var. domestica) with Mycobacterium avium subsp. avium. Avian tuberculosis is one of the most important diseases that affect all species of birds, and is most often caused by Mycobacterium avium and Mycobacterium genavense. 80 out of morethan 600 pigeons were selected based on their clinical signs and poor health conditions and under standard conditions were euthanized, necropsied, followed by bacterial culture on specific media for Mycobacterium avium subsp. avium. Fifty Mycobacterium avium subsp. Avium were isolated from pigeons. All acid-fast bacilli isolates were tested by the PCR assays targeting the 16S rRNA,IS1245 and IS901 genes. After definitive identification of Mycobacterium avium subsp. avium by culturing and PCR assay, 45 fixed samples including liver, gizzard, proventriculus, intestines, kidneys and lungs from positive pigeons were subjected for histopathology studies. Tissues sections were prepared as usual and stained by haematoxylin and eosin, Ziehl-Neelsen and Congo red. Based on gross findings, liver and intestines were the most affected organs. Histologically, caseative uncalcified granulomatous inflammation was noticed in the affected organs. Also histopathology examinations showed that most of the granulomatous lesions in the lungs were in microscopic size and it seems that lungs were affected more than it was expected. In Ziehl- Neelsen’s staining, a large number of acid-fast bacilli were observed within multinucleated giant cells and in necrotic areas. Also in Congo red staining, deposition of amyloid in liver and kidneys sections were observed. In conclusion, histopathology findings were typical of avian tuberculosis, including acid-fast bacilli and uncalcified caseous necrosis centers that were surrounded by multinucleated giant cells, macrophages and lymphocytes.