Histologic Lesions of Thymus and Bursa of Fabricius in Commercial Broiler Chickens Inoculated with H9N2 Avian Influenza Virus

Low pathogenic avian influenza (H9N2) is of major concern for the poultry industry especially in Iran, as the virus can spread rapidly in and between flocks, causing high mortality and severe economic losses. The aim of this study was to determine the pathogenicity of H9N2 avian influenza virus in thymus and bursa of Fabricius of commercial broiler chickens, so we studied the histologic lesions of this isolate in these organs following intranasal (IN) inoculation. Twenty-four 3-week-old chickens were inoculated with 106 EID50 per bird with H9N2 avian influenza virus. Then on days 1, 2, 4, 6, 8 and 10 post-inoculation (PI), samples of the thymus and bursa of Fabricius were collected for histopathological studies. In inoculated chickens, lymphocyte depletion in the thymus, follicular atrophy and cystic follicles in the bursa of Fabricius were seen. The results indicated that the H9N2 has some immunosuppressive effects on chicken lymphoid organs.