Molecular analysis of dengue virus attenuation after serial passage in primary dog kidney cells.

The complete nucleotide sequences of the genomes of dengue-1 virus virulent 45AZ5 PDK-0 and attenuated vaccine candidate strain 45AZ5 PDK-27 have been determined and compared with the dengue-1 virus Western Pacific (West Pac) 74 parent strain from which 45AZ5 PDK-0 was derived. Twenty-five (0·23%) nucleotide and 10 (0·29%) amino acid substitutions occurred between parent strain dengue-1 virus West Pac 74 and virulent strain 45AZ5 PDK-0, which was derived from the parent by serial passage in diploid foetal rhesus lung (FRhL-2) and mutagenized with 5-azacytidine.These substitutions were preserved in the 45AZ5 PDK-27 vaccine. 45AZ5 PDK-0 and PDK-27 strains, which differ by 27 passages in primary dog kidney (PDK) cells, show 25 (0·23%) nucleotide and 11 (0·32%) amino acid divergences. These comparative studies suggest that the changes which occurred between the West Pac 74 and 45AZ5 PDK-0 strains may alter the biological properties of the virus but may not be important for attenuation. Important nucleotide base changes responsible for attenuation accumulated between 45AZ5 PDK-0 and 27.