Virulence of SD16 and SD16-MA viruses in mice.
Groups of five mice were inoculated intranasally with 105 pfu of SD16 or SD16-MA virus. Body weight (A) and survival (B) were monitored daily for 14 dpi. (C) Histopathology of SD16 and SD16-MA infected mice. Lungs were collected at 5 dpi and fixed in 10% formalin, embedded in paraffin and sectioned. SD16 caused mild and limited alveolitis, whereas SD16 induced severe interstitial pneumonia, including diffuse injury of lungs, alveolar collapse, red blood cells and immune cells infiltration. (D) Virus titers in lungs of infected mice. Groups of three mice were inoculated intranasally with 105 pfu of SD16 or SD16-MA viruses and lungs were collected at 3 dpi for virus titration in MDCK cells. Each value represents mean viral yield from three individually infected lungs ± SD. *, P<0.05 compared with the value of SD16.
