HEPATITIS-B VIRUS GENOMIC HETEROGENEITY - VARIATION BETWEEN QUASI-SPECIES MAY CONFOUND MOLECULAR EPIDEMIOLOGIC ANALYSES OF TRANSMISSION INCIDENTS

Nucleotide sequence variability studies were conducted on a 263-base p air fragment of the core-coding genomic region of hepatitis B'virus (H BV), amplified by the polymerase chain reaction (PCR) from three surge ons with varying circulating levels of HBV, all of whom were thought t o have transmitted HBV to their patients post-surgically, DNA sequenci ng was applied to amplicons obtained directly from serum and those clo ned into plasmid vectors, and from single HBV molecules in serum separ ated by a limiting dilution procedure. In one surgeon, who had a titre of similar to 3 x 10(5) genome equivalents ml(-1), the direct sequenc e was identical to none of 29 other sequences and differed by one base substitution from the sequence amplified from the single patient he i nfected. In another surgeon, who had a titre of similar to 2 x 10(6) g enome equivalents ml(-1), the direct sequence was identical to 17 of 3 6 (47%) sequences; however, the sequence common to all three infected patients was identical to a unique sequence in the surgeon that differ ed by three base substitutions from the direct sequence. By contrast, the direct sequence in the third surgeon, who had a titre of similar t o 4 x 10(7) genome equivalents ml(-1), was identical to 25 of 38 (66%) sequences, and to the sequence common to all 11 infected patients. As sessment of HBV DNA sequences directly amplified from clinical specime ns may not be appropriate to studies of transmission in which the sour ce of infection harbours a relatively dilute,heterogenous mix of viral variants.