A Pneumonia-Producing Filtrable Agent from Stock Mice. ∗

Abstract

A virus causing respiratory disease in stock mice has been reported by Dochez, Mills and Mulliken. 1 We have encountered a similar infectious agent, have made a preliminary pathological study of it, and have attempted to compare it with the Dochez virus and with other agents of disease found in stock mice. The chief purpose of this report, however, is to call attention to the ease with which the disease caused by this agent may be confused in mice with infection due to influenza virus.

Pharyngeal washings from patients with a variety of illnesses (common cold, atypical pneumonia, influenza-like illness) were inoculated intranasally into mice which were sacrificed on the sixth day. The lungs were removed aseptically, emulsified, and passed intranasally to normal mice which were in turn sacrificed, the series being continued indefinitely. As controls, serial passages were made from mice inoculated intranasally with pharyngeal washings from normal persons, with broth, and with normal mouse lungs. In every instance, after a varying number of transfers, lung lesions resembling those produced by influenza virus began to appear in the mice. Their initial appearance varied from the first to the ninth passage and they became maximum in 2 or 3 further passages, killing the mice usually on the third or fourth day. White mice purchased in the open market and weighing 5 to 10 g have been used exclusively, and lung lesions have appeared in mice from 2 different dealers. The appearance of the mice before death and the macroscopic appearance of the lung lesions were the same in all mice, irrespective of original source of inoculum, indicating that the infectious agent was present in the stock mice.