Evaluation of H9N2 avian influenza virus dissemination in various organs of experimentally infected broiler chickens using RT-PCR

Widespread occurrence of H9N2 low pathogenic avian influenza (LPAI) viruses in many Asian countriesduring the past decade has resulted in the need for evaluation of the pathogenesis of H9N2 virus infection. In this study, tissue tropism and dissemination of A/Chicken/Iran/772/1998(H9N2) virus throughout the body of broiler chickens were investigated. The clinical signs, gross lesions and antibody titer of the infected chicks were also monitored. Fifty one-day-old commercial broiler chicks were divided randomly into two groups (forty chicks in the experimental and ten chicks in the control group). At the age of five weeks the chicks in the experimental group were inoculated intranasally with the virus. The samples from various tissues were collected at 1, 3, 6 and 9 days post-inoculation (DPI). We used reverse transcriptase/polymerase chain reaction (RT-PCR) assay to evaluate the virus dissemination. Chickens exhibited mild respiratory signs, depression and 5% mortality. Viral RNA was detected in the kidneys on days 3, 6 and 9 PI. The virus was also found in the spleen, trachea and lungs on days 3 and 6 PI. Viral RNA was observed only on day 6 PI in feces. The most remarkable clinical signs and virus detection appeared on day 6 PI. Overall, out of 22 samples taken from each organ of the experimental (dead plus euthanized) birds, 4, 5, 11, 4, and 5 samples from trachea, lungs, kidneys, spleen and feces showed viral RNA, respectively. We could not trace the virus in the blood and pancreas. Data indicated that the number of infected chickens and viral RNA detection from tissues was reduced with increasing antibody titer on day 9 PI. Our findings suggest that the virus has tissue tropism for respiratory, urinary, lymphoid and digestive systems.