Genetic characterization of the complete coding regions of genotype 3 hepatitis E virus isolated from Spanish swine herds

The complete coding regions of five hepatitis E virus isolates of swine origin from two different pig farms and the complete genome sequence of two of these strains were obtained and compared to other full length or partial HEV sequences. Based on the nucleotide sequence, the examined Spanish isolates were 87.1–99.7% similar among them being the closest known strain a Mongolian porcine strain (swMN06-C1056) which shares 84.5–86.1% of the nucleotide sequence, and are also close to other HEV porcine strains from Japan. Two isolates from the same farm presented an 87 nucleotide insertion in the poly-proline hinge unique among all HEV isolates known so far. Comparison with partial HEV sequenced strains indicates that the isolates described in this study form a cluster containing human and porcine HEV strains from Europe, being the only representatives of the subtype 3f that were completely sequenced. Evolutive pressure analysis indicates that microevolution of HEV seems to be driven by negative selection. Further studies should be carried out in order to clarify the HEV origin and evolution.