Figure 1. Cold adaptation and temperature sensitivity of cold-adapted H9N2 influenza virus.

(A) Cold adaptation. Four HAU of cold-adapted (SD/01/10-ca) or wild-type H9N2 (SD/01/10-wt) influenza viruses were inoculated into 10-day-old SPF eggs (three SPF eggs/temperature), and the inoculated eggs were incubated at 25 °C and 35 °C for 48 h. The viral titers in the allantoic fluids were determined by log₁₀ EID₅₀/mL. Data are the mean virus titer of three independent experiments ± the standard errors. (B) Temperature sensitivity. The temperature sensitive phenotype of the SD/01/10-ca or SD/01/10-wt virus was determined by plaque assay in MDCK cells at 33 °C, 39 °C or 41 °C. Data are the mean virus titer of three independent experiments ± the standard errors.