A paralytic disease in nude mice associated with polyoma virus infection.

Nude mice (nu/nu), heterotransplanted with human tumours and kept in isolators, were found to suffer from wasting and posterior paralysis. Electron microscopy of spinal cord tissue revealed virus particles in the oligodendrocytes consistent in size (35 to 40 nm), morphology and distribution with those of the polyoma--SV40 sub-group of papovaviruses. Serology and restriction enzyme analysis of the virus genome showed that the virus was the murine polyoma A2 strain. Inoculation of uninfected nude mice with 10(7) TCID50 of polyoma A2 strain virus produced a similar disease in these mice with wasting and, after 10 to 23 weeks, paralysis of the hind legs of all surviving mice. Extensive myelin disruption was seen throughout the brain stem and sacral region of the spinal cord and high titres of polyoma virus were found in the whole brain (10(8.8) TCID50/brain) and in the spinal cord (10(6.8) TCID50/spinal cord).