Figure 2. Assessment of direct contact-mediated transmissibility of wild-type H9N2 AIVs in guinea pigs.

Groups of three guinea pigs were inoculated i.n. with 10⁶ EID₅₀ SD2/H9N2 (a), SD3/H9N2 (b), JL3/H9N2 (c), or the human influenza virus XD/H1N1 (d). Twenty-four hours later, a naïve contact guinea pig was placed in each cage with an inoculated animal. Nasal washes were collected every two days from all animals beginning 2 days post-infection to detect the presence of virus. Each line represents the virus titer for an individual animal. The dashed lines indicate the lower limit of detection.