Geographical distribution of hepatitis E virus genotypes.

Hepatitis E virus (HEV) is the major agent of acute hepatitis in developing countries where the infection occurs sporadically or in large waterborne e pidemics. HEV, classified in the Caliciviridae, is not culturable. The dete ction of HN RNA by RT-PCR in serum and stool samples is reliable during the 7 to 15 days following the onset of the disease. Restriction endonuclease analysis, cloning and sequencing of PCR products allow a phylogenetic analy sis of HN isolates. Although they belong to a single serotype, strains reco vered from different geographical regions display a significant genetic het erogeneity: Sequencing data from ORF1 and ORF2 regions has led to the chara cterization of 3 distinct genotypes : genotype I gathering the Asian and Af rican subgenotypes; genotype If gathering swine and human US strains; genot ype III limited to the Mexico prototype. Novel variants are currently descr ibed from Africa (Nigeria), China and Europe (Greece and Italy). Each genot ype appears to be related to a well defined geographical area. Nevertheless , a genetic variability is observe within endemic regions such as Asia or A frica. Nigerian endemic isolates especially could represent an intermediate stage in the evolutionary process towards genetic diversity. The animal re servoir: proved by the detection of HEV sequences by PCR among pigs in Nepa l and in the USA, could help to resolve unanswered questions about the orig in of HEV/genotypes, their spread and evolution.