Epidemiology of lymphocytic choriomeningitis in a mouse stock observed for four years

Abstract

A small mouse stock in which lymphocytic choriomeningitis is endemic has been observed over a period of 4 years. The disease has persisted during that time, but it has become so mild that it can no longer be recognized by clinical observation. In spite of this fact, all of the stock mice tested, both young and old, carried considerable amounts of virus in their organs and blood. The females readily transmit the infection to their offspring. Intrauterine infection has become the only mode of transmission of the disease in contrast to the situation in 1935 when a certain number of mice were born virusfree and became infected by contact shortly after birth. The present mildness of the disease appears to be due to two factors, namely, the change in its mode of transmission just mentioned, and a shift in the severity of the disease with regard to the age of the host at the time of infection. This shift has occurred gradually since 1935 when the mice infected in utero were the only ones to become sick. Since 1937, however, the virus is quite harmless for such animals and produces symptoms only in suckling mice from the virus-free stock exposed to contact infection. Evidence is presented which suggests that the shift in the severity of the disease was caused by a decrease of the pathogenicity of the virus for embryonic mouse tissue and a concurrent increase of the resistance to intrauterine infection of the mice from the infected stock. © 1939, Rockefeller University Press., All rights reserved.