Changes in body weight of BALB/c mice infected with different passages of the H10N8 virus. Each mouse in a group was intranasally infected with 105.5EID50 of the virus from different passage (P0, P2, P4 or P6) in a volume of 50 μl. The mice inoculated with lung washes prepared from uninfected mice served as a background control. The body weight of each mouse was expressed as the percentage of its weight on the day after infection. All the P2-infected mice died within 11 days after infection, whereas P4- and P6-infected mice died within 5 days.