Studies on the Pathogenicity of Human-origin Parainfluenza Virus in the Brain of Mice

The pathogenicity of parainfluenza type 2 (croup-associated) virus known to cause infections of the respiratory tract in the early life of man was studied in the brain of mice. One- to 4-day-old sucklings and 4-week-old mice were inoculated intracerebrally with the virus. The virus multiplied in sucklings, but not in adults. Most mice inoculated intracerebrally with the virus appeared healthy. Histological examination showed minimum inflammatory changes, although moderate hydrocephalus developed in three of twenty-one sucklings by 6 weeks post-infection. Immunofluorescent study in sucklings showed viral antigens in ependymal lining cells and choroid plexus epithelium during the first two weeks, and parenchymal cells for more than two months. Virus specific antibody response was observed in adults, but not in sucklings. One interesting finding was that viral antigens persisted in six out of 11 suckling brains for one to two months.