Viremia in mice with pulmonary influenza A virus infections.

Abstract

Abstract Viremia occurs in mice infected intranasally or in the cloud chamber with lethal doses of influenza A (PR8 virus). The incidence of viremia in mice killed at forty-eight hours after infection varied from 20 to 50 per cent in mice allowed to breathe highly lethal clouds of nebulized virus. With few exceptions viremia occurred only in animals after the concentration of influenza virus in the lungs had reached a high level. On the other hand, virus was not isolated from the blood of many animals with similar lung titers so that the incidence of viremia could not be correlated with the amount of virus or the pathologic findings in the lungs. Viremia in experimental pulmonary infections in mice is probably sporadic with the amount of virus in the blood at any one time being small and close to the minimal infecting dose in fertile eggs when inoculated intra-allantoically. The duration of viremia in individual mice could not be determined accurately because of the small amount of blood available for virus analysis. When influenza virus enters the blood from the lungs it quickly becomes attached to the red blood cells. Whether the virus-coated cells become agglutinated in vivo was not determined. Following the intravenous injection of influenza virus it rapidly disappears from the blood but can be detected for significantly longer periods in the spleen, liver, and lung. The possible significance of viremia in relation to the pathogenesis and immune response in experimental infections in mice is discussed.