hMx-tg mice are resistant to infection with THOV but susceptible to DHOV. hMx-tg^+/− and non-tg mice were challenged by i.p. infection with (A) 10³ pfu of THOV (four animals each) or (B) 10² pfu of DHOV (five hMx-tg^+/− and four non-tg). Survival was monitored for 14 d. Mice carrying one functional allele of the endogenous Mx1 gene (Mx1^+/−, five animals) served as positive control for the DHOV challenge experiment. Animals were sacrificed and scored dead when weight loss reached the 25% limit.