ABSTRACT
Avian influenza H9N2 viruses are circulating in domestic poultry worldwide. Although this avian subtype is generally not highly pathogenic for avian species, these viruses have recently been transmitted to mammalian species, including humans. So this study has been done to prescribe the pathologic lesions of this virus in BALB/C mouse as a mammalian mode. We infected 25 female BALB/C mice with 50 micro l of 106EID50 of virus per 50 micro l chorioalantoic fluid. 25 mice as a control group received only 50 micro l of uninfected chorioalantoic fluid. Sampling was done on days 3, 6, 9 and 12 post infection. The following tissues were examined by light microscopy for the presence of lesions and for the detection of Influenza viral antigen [Immunohistochemistry]: lungs, trachea, brain, liver, intestine, spleen, kidneys and heart. Histopathologic studies revealed that this virus only can induce local lesions in lung and trachea in the form of interstitial bronchopneumonia and tracheitis. However these findings showed that Influenza A H9N2 viruses are potential to infect mammals but severity of the lesions differ from sub type to sub type. As the human health have now gained importance, both for illness and fatalities that have occurred following natural infection with avian viruses, and for the potential of generating a reassortant virus that could give rise to the next human influenza pandemic, more consideration and prevention should be applied