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Genetic variability among yellow fever virus 17D substrains.

The complete nucleotide sequence of the genome from two yellow fever (YF) virus strains, 17DD and 17D-213 was determined. Comparison of these sequences with those of other YF viruses, including the parental virulent Asibi strain, allowed the identification of 48 nucleotide sequence differences which are 17D strain-specific and potentially related to viral attenuation. Another 43 nucleotide sequence differences were not common to all 17D substrains and are therefore substrain specific. Of the 21 changes between 17DD and Asibi 15 only five led to amino acid substitutions whereas 13 substrain differences common to all 17D-204 substrains produced six amino acid substitutions. Since the exact passage histories of these viruses is known it was possible to calculate, for each strain, the number of accumulated changes per passage. Based on these data the 17DD strain was the most genetically stable virus.

Amino Acid Sequence↗

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Molecular analysis of yellow fever virus 17DD vaccine strain.

The Oswaldo Cruz Foundation produces most of the yellow fever (YF) vaccine prepared worldwide. As part of a broader approach to determine the genetic variability in YF 17D seeds and vaccines and its relevance to viral attenuation the 17DD virus was purified directly from chick embryo homogenates which is the source of virus used for vaccination of millions of people in Brazil and other countries for half a century. Neutralization and hemagglutination tests showed that the purified virus is similar to the original stock. Furthermore, radioimmune precipitation of 35S-methionine-labeled viral proteins using mouse hyperimmune ascitic fluid revealed identical patterns for the purified 17DD virus and the YF 17D-204 strain except for the 17DD E protein which migrated slower on SDS-PAGE. This difference is likely to be due to N-linked glycosylation. Finally, comparison by northern blot hybridization of virion RNAs of purified 17DD with two other strains of YF 17D virus revealed only genome-sized molecules for all three viruses. These observations suggest that the vaccine phenotype is primarily associated with the accumulation of mutations.

Electrophoresis, Polyacrylamide Gel↗