A Pneumonia Virus of Swiss Mice

Abstract

A virus capable of inducing fatal pneumonia in Swiss mice has been isolated from normal mouse lungs, and its immunological characteristics are now being studied in detail.

Twenty-one groups of normal Swiss mice were inoculated intra-nasally under ether anesthesia with 0.05 cc of lung-suspensions from uninoculated mice. Serial mouse-passage was carried on with each group, using 10% to 30% lung-suspensions. Passages were made at an average interval of 7 days; usually 6 mice were used in each group. The mice were obtained from 6 different breeders. Initially, passages were made without regard to the breeder from whom the mice had been obtained. Lately, however, passages have been made in mice from each individual breeder in order to determine the source of the virus. Definite areas of pulmonary consolidation were present in 43% of the groups in the third serial passage, and in 52% of the groups at the sixth passage. Death occurred as early as the fourth passage, and by the sixth passage deaths were recorded in 24% of the groups. Cultures of the mouse-lung suspensions were made routinely and were sterile in a great majority of instances. Rabbits were injected intraäbdominally with virus-containing material from various passages. They were bled before injection and again 8 to 10 days afterwards. Their serum was tested for the presence of antibodies capable of neutralizing the various strains of virus in the manner described by Magill and Francis. 1

Fatal pneumonia was caused by 0.05 cc of a 10⁻³ to 10⁻⁴ dilution of infected mouse lung, and definite pulmonary consolidation was produced by 10⁻⁵ to 10⁻⁶ dilutions. The virus was filtrable through Berkefeld V and N candles, passed through graded collodion membranes 2 with an APD of 300 mμ and was retained by a Seitz filter.