PVM infection. (A) PVM load assessed by PCR of lung tissue at 2-28 days post-infection. Levels of virus in samples from infected animals at days 2, 4 and 28 were at or below the limits of detection, as were levels in all samples from sham-infected control animals. (B) Mean weights of PVM-infected and naïve mice during the first 3 weeks of life. Significant differences shown as * = P < 0.05, ** = P < 0.01.