Detection of sporadic cases of hepatitis e virus (HEV) infection in china using immunoassays based on recombinant open reading frame 2 and 3 polypeptides from HEV genotype 4

We reported previously on the complete sequence of hepatitis E virus (HEV) genotype 4, isolated from patients with sporadic cases of acute HEV infecti on in China. At least eight HEV genotypes have now been described worldwide , and further isolates await classification. Current immunoassays for the d etection of anti-HEV antibodies are based on polypeptides from genotypes 1 and 2 only and may be inadequate for the reliable detection of other genoty pes. Because genotypes 1 and 4 predominate in China, we wished to investiga te the antigenic reactivities of HEV genotype 4 proteins. Four overlapping regions of open reading frame 2 (ORF2) (FB5, amino acids [aa] 1 to 130; E4, aa 67 to 308; F2-2, aa 288 to 461; E5, aa 414 to 672) and the entire ORF3 product were expressed in Escherichia coli as fusion proteins. Enzyme immun oassays based on each of the five purified polypeptides were evaluated with sera from patients with sporadic cases of acute HEV infection. Individual immunoassays derived from HEV genotype 4 detected more cases of acute hepat itis E than a commercial assay. Some serum samples, which were positive for anti-HEV immunoglobulin G only by assays based on HEV genotype 4, were pos itive for HEV RNA by reverse transcription-PCR. Polypeptide FB5, from the N terminus of ORF2, had the greatest immunoreactivity with sera from patient s with acute hepatitis E. These data indicate that the N terminus or OM may provide epitopes which are highly reactive with acute-phase sera and that assays based on genotypes 1 and 2 alone may be inadequate for the detection of HEV infection in China, where sporadic cases of HEV infection are cause d predominantly by HEV genotypes 4 and 1.