Hepatitis E virus isolated from serological negative Swedish plasma donors belong to different genotype 3 subtypes

Hepatitis E virus (HEV) is a non-eneveloped RNA virus forming the Hepeviridae family. There are four genotypes infecting humans, HEV1-HEV4. HEV1 and 2 infect only humans and are spread in Asia and Africa. HEV3 and 4 also infect animals as pigs, wild boar and deer. HEV4 is mainly found in Asia while HEV3 is globally spread and is endemic in Europe and the USA. The major route of HEV infection is fecal-oral, although parenteral transmission has been described for HEV3. The infection isusuallysubclinical, however,it may develop into clinical and even fulminant hepatitis, and also cause chronic hepatitis in about 60% of infected immunosuppressed individuals. These chronic infected individuals have detectable HEV RNA for up to 6 months before the development of a serological response. During the acute resolving infection anti-HEV IgM and IgG are detected in serum for up to five-six months with declining IgM, and HEV RNA can be detected 1-2 weeks after onset of disease in serum and for an additional two weeks in feces. In this study 18 samples from plasma donors with detectable HEV RNA were investigated, 14 of these donors did not have detectable anti-HEV IgG or IgM. Partial ORF1 encoding for the RNA dependent RNA polymerase was sequenced for 14 of these strains. Phylogenetic analysis revealed that the donors were infected with genotype 3 of different subtypes. The complete or near complete structural region was sequenced. No specific mutation in strains from the anti-HEV negative donors was observed explaining the lack of immune response, and all N-glycosylation sites were conserved and no new could be predicted from the amino acid sequence. This was also true for the phosphorylated ORF3 protein, needed for egress and for the viral encoded methyltransferase and protease. The P and X regions, implicated in virulence and attenuation, could, however, not be amplified. The reason for this is not known but may be due to strong secondary structures of the RNA in this region. Next generation sequencing will be employed for sequencing these regions to investigate possible presence of mutations that may explain the lack of immune response in the donors. If such mutations cannot be identified the lack of immune response may indicate a prolonged viremic phase also in immunocompetent individuals with subclinical HEV infection.