Acute encephalopathy caused by defective virus infection. I. Studies of Newcastle disease virus infections in newborn and adult mice

An acute encephalopathy caused by a defective paramyxovirus infection was studied. Newcastle disease virus (NDV), given intracerebrally, caused neurologic disease and death in mice. Infected newborn mice died by the fourth day after inoculation, and abundant amounts of virus were recovered from their brains. Infected 4 week old mice died by the eighth day, but only minimal amounts of virus, if any, were recovered. The brains of many moribund 4 week old mice were histologically normal and contained no NDV antigen on fluorescent antibody staining. No serum antibody to NDV was detected. These features make this infection difficult to distinguish from a metabolic encephalopathy.