Geographical and ethnic distribution of the HBV C/D recombinant on the Qinghai-Tibet Plateau

Abstract

Two forms of hepatitis B virus (HBV) C/D recombinant have been identified in western China, but little is known about their geographical and ethnic distributions, and particularly the clinical significance and specific mutations in the pre-core region. To address these questions, a total of 624 chronic HBV carriers from four ethnic populations representing five provinces in western China were enrolled in this study. Genotypes were firstly determined by restriction fragment length polymorphism, and then confirmed by full or partial genome nucleotide sequencing. The distribution of HBV genotypes was as follows: HBV/B: 40 (6.4%); HBV/C: 221 (35.4%); HBV/D: 39 (6.3%); HBV/CD: 324 (51.9%). In the 324 HBV C/D recombinant infections, 244 (75.3%) were infected with the "CD1" and 80 (24.7%) were infected with the "CD2." The distribution of HBV genotypes exhibited distinct patterns in different regions and ethnic populations. Geographically, the C/D recombinant was the most prevalent HBV strain on the Qinghai-Tibet Plateau. Ethnically, the C/D recombinant had a higher prevalence in Tibetan patients than in other populations. Clinically, patients with HBV/CD1 showed significantly lower levels of serum total bilirubin than patients with HBV/C2. The prevalence of HBeAg was comparable between patients with HBV/CD1 and HBV/C2 (63.3% vs 50.0%, P = 0.118) whether patients were taken together or stratified by age into three groups (65.6% vs 58.8% in <30 years, P = 0.758; 61.9% vs 48.0% in 30-50 years, P = 0.244; 64.3% vs 33.3%, P = 0.336). Virologically HBV/CD1 had a significantly lower frequency of G1896A than HBV/C2. In conclusion, the HBV C/D recombinant is restricted to the Qinghai-Tibet Plateau in western China and is found predominantly in Tibetans. The predominance of the premature pre-core stop mutation G1896A in patients with the HBV C/D recombinant may account for the higher prevalence of HBeAg in these patients.

Figure 1. Distribution of HBV genotype by geographical location in western China.

The proportion of the HBV C/D recombinants (‘CD1’ and ‘CD2’) in each region is shown. The complete names of regions mentioned in this figure are as follows: XJ = Xinjiang, QH = Qinghai, GS = Gansu, NX = Ningxia.

Figure 2. HBeAg positivity in patients of HBV/CD1 or HBV/C2.

Patients were stratified by age into three groups, younger than 30 years (<30), 30–50 years and older than 50 years (>50). The prevalence of HBeAg decreased with age in patients of HBV/C2 (58.8% in <30 years; 48.0% in 30–50 years; 33.3% in >50 years), whereas almost no change was observed in patients of HBV/CD1 (21 of 32, 65.6% in <30 years; 39 of 63, 61.9% in 30–50 years; 9 of 14, 64.3% in >50 years). The rate of HBeAg positivity did not reach the statistical significance in all three age groups between HBV/CD1 and HBV/C2 (P = 0.758, 0.244 and 0.336 in <30, 30–50 and >50 years respectively).

Figure 3. Phylogenetic analysis of backbone sequences of the HBV C/D recombinant compared with reference strains representing genotypes A–G.

Accession numbers and sample numbers are shown on each branch, and are indicated on the left by the HBV genotype or subgenotype. Bootstrap values are shown along each main branch. Scale bars indicate the nucleotide divergence. Isolates determined in this study are marked. A, Phylogenetic tree based on nt 800–3215. B, Phylogenetic tree based on nt 1500–3215.

Figure 4. Phylogenetic analysis of mosaic sequences of the HBV C/D recombinant compared with reference strains representing genotypes A–G.

Accession numbers and sample numbers are shown on each branch, and are indicated on the left by the HBV genotype or subgenotype. Bootstrap values are shown along each main branch. Scale bars indicate the nucleotide divergence. Isolates determined in this study are marked. A, Phylogenetic tree based on nt 10-799. B, Phylogenetic tree based on nt 10-1499.