Abstract
Severe necrotising hepatitis, with microscopic brain lesions containing multi-nucleated giant cells, was observed in specified-pathogen-free nu-nu mice, contained in a semi-protected environment, but within the same room as other, conventional, mice. An entire group of 40 nu-nu mice died within a month, with no evidence of bacterial or parasitic infection. However, cell-free liver filtrates reproduced the liver lesions in specified-pathogen-free Swiss-Schneider mice injected intraperitoneally at up to 21 days of age, but not in baby rats and hamsters.
Electronmicroscopy showed masses of particles resembling mouse hepatitis virus in the liver lesions of the recipient mice, and the identity of the virus was further confirmed serologically and by its physical properties. It was concluded that the infection was caused by a neurotropic variant of mouse hepatitis virus and could have originated from the conventional mice kept in the same room.