A Virus from Cases of Influenza-like Upper-respiratory Infection

Abstract

During the past few years at least two groups of investigators, have reported cases of upper-respiratory infection of unknown etiology, that resembled true “epidemic influenza” in clinical respects but which differed in that the convalescent serums failed to show any increase in capacity to neutralize standard strains of the influenza virus. Two similar cases of influenzalike infection occurred among the workers in this laboratory in February, 1940. The serums obtained from these cases 4 weeks after the infection and those obtained either at the time of or 3 weeks before the onset of illness were tested against the PR8 strain of the virus of epidemic influenza. Neither of the convalescent serums showed any detectable increase in capacity to neutralize the usual 1000 lethal doses of the virus; and neither of them fixed complement in tests against antigens prepared in the usual manner from mouse lung suspensions. This apparent lack of development of antibodies reactive against this standard strain of influenza virus seemed to indicate that the influenza-like infection of neither of the cases had been due to the virus of epidemic influenza. The throat washings from both patients when inoculated intranasally in ferrets under ether anesthesia evoked a fever of the type considered characteristic of influenza. The infectious agent from one of the cases was transmitted serially in ferrets, but even after 10 passages the lungs of infected animals showed no consolidation. The infection was transmitted by intranasal inoculation from ferrets to Swiss mice; in that species blue-gray areas of pulmonary consolidation were produced on the first passage. After 9 passages the virus increased sufficiently in virulence to kill some of the mice but although it has now been passed over 20 times it has not yet acquired the capacity of regularly killing all of the mice that are inoculated.