2.4 Experimental infection of mice
170 six-week-old healthy BALB/c female mice were randomly divided into seventeen groups of 10. Mice in PRV-injected groups were inoculated subcutaneously (s.c.) with 500 μL different isolates respectively. Mice in DMED-injected group were inoculated with 500 μL DMEM as control. After the inoculation, the mice were examined daily for clinical signs for 7 days.