The growth of duck hepatitis virus in ducklings
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The growth patterns of the Houchin strain of duck hepatitis virus in different tissues of ducklings infected when 11 days old were similar but their magnitudes and the times at which virus growth occurred differed significantly. The virus multiplied best in the liver and less well in kidneys, spleen, small and large intestines, and pancreas. Virus present in bile was attributable to virus excreted from the liver. Virus in other tissues was attributable to the virus content of blood. Virus was recovered from cloacal swabs taken from infected ducklings from 24 hours after exposure and excretion continued for a further 11 days.Age -related resistance to duck virus hepatitis was manifested in ducklings by a decline in the mortality rate as the birds grew older and was linked to a lengthening of the lag phase of virus growth, to a steady depression of virus growth, and to a shortening in the period of virus excretion. Multiplication rates of the virus, however, were not affected.An age- related resistance was found also in chicken embryos and duck embryos infected with the Houchin strain of duck hepatitis virus. A strain, H56, adapted to chicken embryos by serial passages overcame this age -related resistance in chicken embryos.