Propagation in Chick Embryos of Dengue Virus,Hawaiian Strain. II. Findings in Infected Eggs. ∗

Summary

1. The Hawaiian strain of dengue virus has been propagated in chick embryos through more than 90 passages in a series initiated with virus derived from the 101st intracerebral passage in mice. Certain characteristics of the infection of chick embryos have been described in this paper. 2. Susceptibility of chick embryos decreases with increasing age, highest titers being obtained in embryos 4 to 5 days old at the time of inoculation. 3. While sustained propagation of the virus in eggs initially required secondary incubation of more than 5 days, in later egg passages the virus attained maximum titers after 5 days. There was a slight decrease in viral concentration after the seventh day. 4. The infectivity of the virus for chick embryos is of the same order of magnitude as that for mice. 5. Infection with dengue virus does not result in discernible lesions in chick embryos, nor does it appear to affect their growth or their hatchability. 6. The concentration of virus in embryonic brain and spinal cord tissue is 100 to 1000 times higher than in other tissues, with minimal amounts found in extra-embryonic membranes and fluids. 7. Virus has been found to persist in the CNS of chicks until at least ten days after hatching, 22 days after inoculation into the egg. Minimal amounts of virus, much less than present in the CNS, have also been found in the blood of chicks two days after hatching.