Hepatitis E virus: identification of type-common epitopes

Large epidemic outbreaks of enterically transmitted non-A, non-B viral hepatitis (ET-NANBH) have been documented in developing countries. A molecular clone derived from the causative agent, the hepatitis E virus (HEV), has recently been described (G.R. Reyes, M.A. Purdy, J.P. Kim, K.-C. Luk, L.M. Young, K.E. Fry, and D. Bradley, Science 247:1335-1339, 1990). We now report the isolation, by serologic screening, of two cDNA clones derived from a fecal sample collected during a 1986 outbreak of ET-NANBH in Telixtac, Mexico. The cDNA clones encode epitopes that specifically reacted with acute- and convalescent-phase sera collected during five different ET-NANBH epidemics and represent the initial cloning of the Mexico strain of HEV. Recombinant fusion proteins expressed from these clones were also recognized by antibodies from cynomolgus macaques experimentally infected with HEV. The cDNA clones were shown to be derived from HEV by their specific hybridization to the previously recognized full-length genomic RNA transcript of approximately 7.5 kb. In addition, however, subgenomic polyadenylated transcripts of approximately 2.0 and approximately 3.7 kb were also identified in HEV-infected cynomolgus monkey liver. Sequences homologous to the epitope clones were isolated from the Burma strain of the virus, and these demonstrated reactivity comparable to that seen with the Mexico strain epitopes. When compared with the available full-length sequence of the Burma strain of HEV, it was discovered that the cDNA clones were encoded in different open reading frames (ORFs). The comparison between Mexico and Burma HEV strains indicated amino acid homologies of 90.5 and 73.5% for these epitope-encoding clones derived from ORF2 and ORF3, respectively. The identification of these clones not only has provided insight into the expression strategy of HEV but has also resulted in a source of recombinant protein useful in the diagnosis of HEV-induced hepatitis.