We evaluated the pathogenicity of the virus in mice and found that it could efficiently replicate in the lungs of mice with high lethality (10 2.25 pfu per MLD 50 ). To determine the optimal dose of inoculation, 10 mice in each group were infected i.n. with 10 1.5 , 10 2.5 or 10 3.5 pfu viruses, and the signs, body weight, and mortality were monitored daily for each group for 14 days. Pilot experiments indicated that a dose of 10 2.5 pfu was optimal, because the course of the disease was prolonged and the mice presented with obvious signs of respiratory illness.