Replication of the m41.1ko virus in C57BL/6 and Bak1−/− mice. C57BL/6 or Bak1−/− mice were infected either intravenously (A to C) or intraperitoneally (D and E) with 2 × 105 PFU/mouse. On days 3 (A and D) and 10 (B and C) or 14 (E) postinfection, mice were sacrificed. Virus titers in the spleen, lungs, and SGs were determined by plaque assay. Statistical significance was assessed using the Mann-Whitney test (*, P < 0.05; **; P < 0.01; ns, not significant). DL, detection limit.