Figure 1. Assessment of morbidity and mortality in newborn mice infected with circulating CA16 CC024, CC045, CC090, CC097, CC163, the prototype G10 and SHZH05 viruses.

One-day-old ICR mice were intracerebrally inoculated with different virus strains at 10^4.5 CCID50 ml⁻¹ or MEM cell culture medium. Survival rates and clinical scores were then monitored and recorded daily after infection. Control mice were given cell culture medium instead of virus suspension. Each group contained 8–10 mice, and results were obtained from three independent experiments. Varying grades of clinical disease were identified as: 0, healthy; 1, lethargy and inactivity; 2, wasting; 3, limb shaking and weakness; 4, hind-limb paralysis; 5, moribund or dead.