MAVS and viral load: To determine whether the absence of IPS-1 would increase the severity of viral disease, WT and IPS-1−/− neonatal mice were intranasally inoculated with a low inoculum (2 pfu) of PVM or vehicle (DMEM/10% FCS) at 7 days of age and killed at 4, 7, 10 and 14 days post primary infection (dpi).