Natural infection of nude mice with low-virulent mouse coronavirus

The outbreak of wasting disease of nude mice occurred in the laboratory colony of a Pharmaceutical Company. The viruses producing cytopathic effect with syncytium formation were isolated from the wasted nude mice by DBT cells, and were identified as mouse coronavirus by direct immunofluorescence. The nude mouse colony was closed and all the nude mice (about 500) were killed by the reason of disease control. At autopsy about 60% of nude mice showed necrotic hepatitis. By the virus isolation to see the source of contamination, viruses were isolated from the feces of apparently healthy mice of ICR, CDF1, DBA/2 and C3H, and from human cancer cell line stocked in liquid nitrogen. In experimental infection, the isolates produced only mild hepatitis in ICR mice treated with cortisone. By cross-neutralization test, the nude isolate reacted closely with the virus from C3H mice but not with the virus from cancer cell line. The isolates from nude and C3H mice produced experimentally wasting disease with necrotic hepatitis in nude mice. These findings suggest that wasting disease in nude mice might be caused by low-virulent mouse coronavirus shed in feces from C3H mice introduced before the outbreak of disease.