Figure 1. Replication and direct contact transmission of H9N2 viruses.

Ferrets were inoculated intranasally (i.n.) with 10⁶ TCID₅₀ of H9N2 viruses RGWF10 (A), Dk/HK/Y280/97 (B), RGQa88 (C), Ck/HK/SF3/99 (D), and Ck/Jordan/554/03 (E). Twenty-four hours later, one naïve ferret (direct contact) was added to the same cage as each of the infected ferrets. Nasal washes were collected daily and were titrated in MDCK cells. Black, white and gray bars represent individual ferrets sampled and the amount of viral shedding at different days pi. The titers are expressed as log₁₀ values of TCID₅₀/ml with the limit of detection at 0.699 log₁₀TCID₅₀/ml. The dotted line was arbitrarily set at <0.3 log₁₀TCID₅₀/ml in order to represent samples below the detection limit. L and Q correspond to Leu226 and Gln226, respectively in the HA RBS.