Figure 1
N7-MTase mutants are safe for ducklings. A Scheme of infection. 5 day-old specific pathogen free (SPF) ducklings were intramuscularly injected with 200 µL of DMEM containing 104.75FFU/mL WT virus or N7-MTase mutants or live attenuated DTMUV vaccine WF100 strain, while 200 µL of DMEM was intramuscularly inoculated as a mock control. Infected ducklings were monitored for 14 days for clinical signs of disease (n = 10), body weight changes (n = 3), and survival (n = 10). B clinical symptom scores. The data are presented as the means ± SDs. **p < 0.01 (one-way ANOVA). C body weight changes of ducklings. D Virulence of mutant viruses in ducklings. The statistical significance of survival was analyzed using a survival curve and the log-rank (Mantel–Cox) test, **p < 0.01. E Necropsy of ducklings of WT and mutant groups. F, G ducklings were sacrificed at 6 dpi, brain (F) and spleen (G) were collected for histological analysis. The black arrow indicates pathological injury. Scale bar, 100 μm.