Genetic Diversity, Occult Hepatitis B, and Mutational Signatures in Migrants from Regions with Varying HBV Endemicity: Importation of Diverse Viral Variants into St. Petersburg, Russia.

The importation of hepatitis B virus (HBV) variants through migration challenges elimination efforts in low-endemicity countries. This study evaluated the seroprevalence, occult hepatitis B infection (OBI), and molecular signatures of HBV among 537 international migrants from 46 countries who arrived in St. Petersburg, Russia. HBsAg, anti-HBs, and anti-HBc were measured by ELISA. This was followed by nested real-time PCR targeting viral genes (S, X) and a human housekeeping gene (HPRT, internal control), amplification of overlapping fragments covering the complete HBV genome, and Sanger sequencing. HBsAg prevalence was 2.61% (95% CI: 1.43-4.34), while anti-HBc was detected in 16.39% (95% CI: 13.36-19.79). HBV DNA was found in 8.19% (44/537; 95% CI: 6.02-10.04) of migrants. Notably, OBI (HBsAg-negative/HBV DNA-positive) was identified in 33 individuals, yielding a prevalence of 6.15% (33/537; 95% CI: 4.27-8.52) in the entire cohort and 6.31% among HBsAg-negative subjects. The findings among OBI cases were as follows: the majority (54.5%) had no detectable anti-HBc or anti-HBs; 30.3% were positive for anti-HBs only; 6.06% were positive for anti-HBc IgG only; 9.09% of cases featured both anti-HBc and anti-HBs. Viral loads in OBI cases were uniformly low (14-53 IU/mL). Genotype D predominated (86.36%, 38/44). The distribution of subgenotypes among all sequenced isolates was as follows: D1 in 36.36% (16/44), D2 in 36.36% (16/44), D3 in 13.64% (6/44), while genotypes A2 (6.82%, 3/44), B4 (4.55%, 2/44), and C2 (2.27%, 1/44) were rare. In the major hydrophilic region (MHR), the most frequent amino acid substitutions were at positions T127P/I (61.4%) and T118R/M/V/A (45.5%). Immune escape mutations were significantly associated with OBI (81.82% of OBI cases versus 18.18% of HBsAg-positive cases;