SYNERGISTIC ACTION OF HEMOPHILUS INFLUENZAE SUIS AND THE SWINE INFLUENZA VIRUS ON THE CHICK EMBRYO

THE COURSE OF EXPERIMENTAL INFECTION OF THE CHICK EMBRYO WITH THE VIRUS OF EQUINE ENCEPHALOMYELITIS

The titration curve for the virus of Eastern equine encephalomyelitis inoculated into the 10 day old chick embryo shows that the maximum increase in virus content continues until shortly before the generalized destruction of the embryo is apparent. This is followed by a stationary phase. Histological studies of infected embryos fail to demonstrate selective tissue destruction, and titrations show the virus to be distributed throughout the egg, although concentrated in the embryo. The chorioallantoic membrane gradually becomes increasingly resistant with age to both the Eastern and Western viruses. Increased resistance with age is also apparent in the hatched chick. These findings are based on the use of the chick embryo itself as the test animal to determine the 50 per cent mortality end-point. The limits of accuracy of this method are defined.

Non-specific resistance to experimental cholera in embryonated eggs

It has been confirmed that 11- and 13-day-old chick embryos are susceptible to lethal infection with minute inocula of V. cholerae, while 15-day-old embryos are relatively resistant. Twenty strains of E. coli were found to vary in their capacity to kill chick embryos, without relationship to their human enteropathogenicity. Prior infection of 13-day-old embryonated eggs with E. coli strains selected for low embryo virulence had a marked protective effect against superinfection with V. cholerae. This effect was duplicated by pretreatment of embryos with killed E. coli cells or endotoxin preparations but not with a suspension of killed cells of a Gram-positive species. Preparatory E. coli infection induces a phase of vibriostasis in the 13-day-old egg which may be sufficient to tide the embryo over into the phase of relative insusceptibility associated with age. Younger embryos exhibit only a lag in death under similar conditions. The chick embryo is presented as a potentially valuable tool for the study of combined infections and of the mechanisms of natural resistance.

SULFONAMIDE CHEMOTHERAPY OF COMBINED INFECTION WITH INFLUENZA VIRUS AND BACTERIA

1. Sulfonamide chemotherapy controls the bacterial component of combined infection with influenza virus and pneumococci in rats. 2. Reinstillation of fluid (broth, physiological salt solution) into the respiratory passages of mice several days after sublethal viral infection converts the viral infection into a lethal one. 3. Sulfonamide chemotherapy controls the bacterial component of combined bacterial and viral infection of mice, produced by intrabronchial inoculation of mixtures of bacteria and sublethal or lethal doses of virus. 4. Bacterial pneumonia may be superimposed upon sublethal viral infection in mice by inhalation of fine droplets of bacterial suspension several days after inoculation of virus. Normal mice inhaling fine droplets of bacterial suspension fail to develop obvious disease. 5. Sulfonamide chemotheiapy controls bacterial pneumonia superimposed on sublethal viral infection by inhalation of fine droplets of bacterial culture. 6. The secondary bacterial penumonia does not convert the sublethal viral infection into a lethal one. 7. If another pandemic of influenza occurs, it is probable that sulfonamide chemotherapy will be valuable in the treatment of secondary bacterial pneumonia and will be effective in lowering the case fatality rate if the viral component of the infection is not severe enough by itself to cause death.