Evidence for quasispecies distributions in the human hepatitis A virus genome.

Nucleotide sequence analysis of multiple molecular clones of the hepatitis A virus (HAV), generated by reverse transcription-PCR of two capsid-coding regions, revealed a degree of heterogeneity compatible with a quasispecies structure in three clinical samples. Passage of plaque-purified reference strain HAV pHM175 43c in FRhK-4 cells documented the generation of a mutant distribution of HAV genomes. The mutant spectra showed mutation frequencies in the range of 1 x 10(-3) to 1 x 10(-4) substitutions per nucleotide, with a dominance of transition over transversion mutations. While in the VP3-coding region, nonsynonymous mutations were predominant; in the VP1-coding region they were uncommon. Around 50% of the amino acid replacements involved residues located at or near antigenic sites. Most of the detected mutations occurred at or in the vicinity of rare codons, suggesting a dynamics of mutation-selection, predominantly at and around rare codons. The results indicate that despite antigenic conservation, HAV replicates as a complex distribution of mutants, a feature of viral quasispecies.