Histopathological Study of A/chicken/iran/772/99 (h9n2) Influenza Virus in Commercial Broiler Chickens

Avian influenza outbreaks in 1998 due to H9N2 subtype of avian influenza virus (AIV) that occurred in poultry industry in Iran caused serious economic losses. The aim of this study was to investigate the pathogenesis, clinical signs, gross and histopathological findings of the chickens experimentally inoculated with A/Chicken/Iran/772/99(H9N2) influenza virus, isolated from the commercial broiler chickens of Iran with 60% mortality. Eighteen 3-week-old commercial broiler chickens were inoculated with 10 EID50 per bird with A/chicken/Iran/772/99(H9N2) avian influenza virus. On days 1, 2, 4, 6, 8 and 11 post-inoculation (PI) samples of the trachea, lungs, liver, pancreas, spleen, thymus, duodenum, kidneys, brain and bursa of Fabricius were collected for histopathological study. Clinically, depression, crouching, huddling, puffing, oedema of face and head, conjunctivitis and ruffled feathers were observed. In necropsy, turbidity of the thoracic and abdominal air sacs and mild congestion of the trachea and lung and mild accumulation of fibrinous exudate on the tracheal mucosa were seen. Tracheitis, pneumonia and tubulointerstitial nephritis were the most frequent histological lesions. The results indicated that the A/Chicken/Iran/772/99 (H9N2) avian influenza virus has pathogenicity for the trachea, lungs (pneumotropic) and kidneys (nephrotropic).