Pathogenicity of mouse hepatitis virus for mice depending upon host age and route of infection.

Day-old to 4-week-old mice from a breeder colony which had been seromonitored to be free from mouse hepatitis virus infection, were tested for susceptibility to the virus by different routes of inoculation. After intraperitoneal, intravenous and intracerebral inoculation of 10(2) or more plaque-forming units of the virus, mice of all ages died of acute hepatitis. While day-old mice died also after subcutaneous, intranasal and peroral routes of inoculation, those 3 weeks or more of age resisted to infection by these routes. To intranasal inoculation mice 1 and 2 weeks of age were fully susceptible but some of the resisted to peroral inoculation. In the course of non-fatal infection in 4-week-old mice after intranasal inoculation, viremia and production of some hepatic lesions were recognized and infection became fatal in association with cortisone treatment. The results suggested that the intranasal route of infection may be of importance for spreading of infection in mouse breeding colonies in which inapparent infection is prevailing.