Figure 1.

Murine adaptation of CA/07 increases virus replication in lungs and spread to brain. (A,B) Swiss Webster mice were infected with CA/07, and recovered virus was passaged lung-to-lung nine more times, for a total of ten passages. Morbidity was determined by monitoring weight loss over time ((A), passages 1, 5 and 10), and virus titers in the lung were measured by the 50% tissue culture infectious dose (TCID₅₀) assay (B). (C) Dissemination of parental CA/07 and passage 10 (CA/07-MA (mouse adapted)) virus was analyzed by performing TCID₅₀ assays on brain and spleen homogenates. N.D. = not detected. In (A–C), error bars represent the standard deviation (n = 4 mice).