Figure 4.

Pathogenicity of the isolated viruses in mice. Five mice per group were intranasally inoculated with the viruses at 10⁶ EID₅₀ (50% embryo infectious dose). (a) Body weights during 14 days of monitoring. Values represent the average score of overall body weight loss compared with the initial body weight ± standard deviation (SD). The change in body weight of mice infected with F076 was more obvious (p < 0.005). (b) Percentage survival of mice infected with the influenza viruses. (c–f) Heart, liver, spleen, lungs, kidneys and brain were collected from the infected mice (n = 3) on the indicated days post-infection (dpi) and viral titers were determined in 9-day-old specific-pathogen-free embryonated eggs. Influenza strains: F076 (A/Hebei/F076/2018, human, associated with severe illness in 2018), HB17 (A/Hebei/HB17/2017, human, associated with severe illness in 2017; control), CA04 (A/CA/04/2009, pandemic flu virus; control), and 16275B (B/Hebei/16275B/2018, human, associated with severe illness in 2018).