Direct Transmission of Human Influenza Virus to Mice

Abstract

Repeated attempts have been made to isolate human influenza virus by the direct inoculation of mice with material obtained from patients acutely ill with the disease. Up to the present, however, the establishment of experimental influenza in mice has been successful only when the virus was first subjected to primary passage in ferrets.

In December, 1936, strains of human influenza virus were isolated from fresh cases of influenza occurring in New York. Following one ferret passage, the strains were transferred to mice and became so rapidly adapted to this species of animal that deaths occurred among the mice of the second passage. The ease with which these results were obtained heightened the possibility of transmitting the virus infection directly from human throat washings to mice without intermediate ferret passage.

With plain meat infusion broth as the medium, nasal and pharyngeal washings were collected from 2 patients acutely ill with influenza. The washings were pooled. One portion was used for ferret inoculation and yielded a strain of virus which was readily transferred from ferret to mice. The remainder was stored in the frozen state at —78°C. for 19 days. It was then removed from storage, allowed to thaw at room temperature and centrifugalized at 2500 revolutions per minute for 30 minutes. The supernatant fluid was then centrifugalized in the air-driven centrifuge 1 at 14,000 r.p.m. for 3 hours. The supernatant fluid was removed, the sediment was resuspended in the supernatant to 1/6 the original volume and anesthetized mice were then given 0.05–0.08 cc. of the material intranasally.

Serial passages were made in mice at 4 to .i-day intervals. A heavy suspension (50 to 7070) of the finely ground lung tissue from inoculated mice was given intranasally to normal mice. During the first 3 passages no significant pulmonary lesions were observed. It was shown, however. that virus n-as present in the lungs of the third passage mice, since a ferret inoculated intranasally ivith a suspension of these lungs dei-eloped the characteristic signs of experimental influenza and subsequently developed neutralizing antibodies against human influenza virus.