Phylogenetic and recombination analysis was performed on 32 complete hepatitis E virus (HEV) genomes from infected humans and pigs. For the first time, evidence for recombination between divergent HEV strains was obtained, with at least two strains being found to have discordant phylogenetic relationships consistent with the occurrence of intragenotype recombination. This finding confirms that humans can be dually infected with divergent HEV strains and has implications for the emergence and evolution of new HEV epidemics.Hepatitis E virus (HEV) is a causative agent of enterically transmitted hepatitis disease and, apart from infections of pregnant women, is generally associated with low mortality (11,17). Outbreaks of HEV have been described to occur in many regions of the world, including Asia, Africa, and Mexico (1, 33, 53), while sporadic cases have been documented in the United States, Africa (9), and Europe (27,37,38,60). HEV is presumed to be a zoonotic disease, as surveys of both wild and domestic animals have found evidence for human-related HEVs in rats (12, 22), pigs (2,7,21,29,32,56), deer (45), and wild boar (41). Direct animal-to-human transmission of HEV has been demonstrated, for example, from deer to human as a result of eating uncooked meat (45). Interestingly, HEV characterized from swine in countries where HEV is not endemic is usually closely related to cases of sporadic human HEVs from the same country, for example, in the United States and Japan (29,30,42,57), while in India, where HEV is endemic, human and swine HEV strains are not closely related (2). This suggests that in certain regions HEV is more established in the human population and that in other regions HEV is emerging as a result of direct contact with animal reservoirs for the virus. Divergent HEVs with no human counterparts have also been found in chickens (avian HEV). Avian HEV shares only 50 to 60% nucleotide sequence identity with HEV from humans and swine (15,16).HEV is a positive single-stranded RNA virus that is approximately 7,200 nucleotides (nt) in length. HEV's genome is capped and polyadenylated and has three open reading frames (ORF) (Fig. 1). As the organization of HEV's genome resembles that of Caliciviridae, at one time it was considered a mem-FIG. 1. Genomic organization of HEV. The scale at the bottom of the figure corresponds to nucleotides (in thousands). ORF1 encodes a nonstructural polyprotein which provides guanylyl-methyltransferase and RNA-dependent RNA polymerase activities and possibly other functions (23,25). The ORF2 and ORF3 proteins are believed to be encoded by individual subgenomic RNAs generated during replication (44, 58). ORF2 encodes the viral capsid protein; ORF3, which contains one potential phosphorylation site, encodes a very small protein of about 123 amino acids (59). ORF3 proteins partition with the cytoskeleton, and it has been suggested that an interaction between ORF2 and ORF3 is associated with the assembly of virions (47,50). ORF3 is also believed to interact with proteins involv...