Mouse adapted NS1 mutations increase virulence in CD-1 mice.

Groups of 5 female CD-1 mice were infected intranasally with 5×106 PFU dose of rHK NS MA or HK-wt virus. NS1 mutant M106V + M124I was inoculated at dose of 2.5×106 PFU due to insufficient viral stock titre. Survival (A) and body weight loss (B) were monitored for 14 dpi. Percent body weight is expressed as the mean value of 5 (or total number alive) mice (*p<0.05, **p<0.01, ***p<0.001; two-tailed unequal variance paired student's t-test for days 1–6). Experimental endpoint was defined as >30% body weight loss and respiratory distress. Graphical analysis of data was broken into three mutant sets, with rHK-wt included in each, due to the number of mutants surveyed.