FIG 8.

In-contact transmission of viruses derived from P9 virus-derived L2, N9, and L18 viruses in pigs. Groups of three pigs (4 to 5 weeks old) were infected intranasally with 10⁶ TCID₅₀ of L2 (A), N9 (B), L18 (C), and parental control rHIN1 (D) viruses. Three naive animals were introduced into each group 24 h later. Unlike parental rH1N1 virus, all three P9-derived viruses were efficiently transmitted to all in-contact pigs. Virus titers in nasal swabs were determined by TCID₅₀ assays on MDCK cells at the indicated dpi or dpc. The horizontal dashed line corresponds to the TCID₅₀ assay detection limit. Each bar represents the virus titer from an individual animal.