Identification of novel human hepatitis E virus (HEV) isolates and determination of the seroprevalence of HEV in Korea

Abstract

Hepatitis E virus (HEV) was originally identified as the causative agent of enterically transmitted non-A, non-B hepatitis. Recently, HEV isolates were subsequently identified in humans and swine in many countries, including Korea. Also, public concerns regarding HEV as a potential zoonotic agent have been increasing. Therefore, we attempted to identify HEV from Korean sera and compare the nucleotide sequences with those of previously identified HEV isolates from other countries. In our study, viral RNA was purified from 568 human sera collected from different regions of Korea. Nested PCR and reverse transcriptase PCR were developed based on the nucleotide sequences of open reading frame 2 (ORF 2) of U.S. and Japanese HEV isolates from humans and Korean HEV isolates from swine. After amplification of the HEV ORF 2 gene from 14 serum samples that were collected mainly from rural areas (2.64% prevalence of HEV viremia), the gene was cloned and sequenced. The isolates were classified into seven different strains, all of which belonged to genotype III. The human isolates we identified were closely related to three Korean swine isolates, with 99.2 to 92.9% nucleotide sequence homology. Our isolates were also related to the Japanese and U.S. HEV isolates, with 99.6 to 97.9% amino acid sequence homology. Human sera were collected from 361 individuals from community health centers and medical colleges. With respect to seroprevalence, 11.9% of the Korean population had anti-HEV immunoglobulin G (IgG). In individuals ranging in age from 40 to over 60 years, the prevalence of anti-HEV IgG was demonstrated by a seroprevalence of almost 15%, especially among populations in rural areas. This is the first report on the identification of human HEV in Korea. Overall, this study demonstrates that subclinical HEV infections may prevail in human populations in Korea and that there is a strong possibility that HEV is a zoonotic agent.

FIG. 1.

Phylogenetic tree analysis of isolates of Korean human HEV by comparison of the conserved 720-bp regions of ORF 2 in swine and human HEV isolates. The HEV genotypes are according to a recent report (18). The GenBank accession numbers of the HEV isolates used in this study are given in Materials and Methods. The bootstrap values are percentages.

FIG. 2.

Age-dependent distribution of anti-HEV antibodies in human individuals (each diamond represents one individual). The presence of anti-HEV antibodies was determined by using a commercial HEV IgG ELISA kit (Genelabs Diagnostics, Singapore) according to the manufacturer's instructions. The cutoff value was also determined by a calculation suggested in the manufacturer's instructions. OD₄₉₂, optical density at 492 nm.