Comparison of the infectivity of influenza Viruses in two host Systems: the Allantois of infect Eggs and Surviving Allantois-on-Shell

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Abstract
It is shown that the assay for infectivity in bits of allantois-on-shell, which has been standardized on the BEL strain, is optimal also for nine representative strains of influenza virus tested. On the average, the sensitivity of the technique is the same as of orthodox allantoic infectivity tests; its precision is always higher. The relative sensitivity of the two tests varies from strain to strain, the log tray/egg differences being SW (+0.88), MEL (+0.51), CAM (+0.31), PR8 (0.28), WSE (+0.25), HUT (−0.02), BEL (−0.22), FMI (−0.35), LEE (−0.47), BON (−1.02). This gradient is the same for fully infective and incomplete forms of influenza virus. The tray/egg gradient of susceptibility is negatively correlated with the variation in host resistance. The differences in susceptibility are not due to any effect of the plastic trays, to thermal inactivation of the virus, to differences in adsorption or viropexis in the two test systems or to the effect of allantoic fluid on the virus particle. The critical step has been shown to occur during the intracellular stage of multiplication.