First Identification of HEV Subtype 3i in Human Hepatitis E Cases in Central Italy

HEV genotype 3 is classified into several subtypes. In Italy, 3f, 3c, 3e and, rarely, 3a subtypes are usually detected in human hepatitis E cases: the present study documents, for the first time, the detection of the 3i subtype, previously described in Italy exclusively from wild boars. Routine surveillance by short Sanger sequences highlighted five hepatitis E cases with unusual HEV subtype between 2019 and 2023 in a small geographical area in Umbria, Central Italy. Further characterization of the whole HEV genome by NGS was successful in three of them. Through phylogenetic and p-distance analysis, all the sequences could be classified as subtype 3i, and three of them proved to be highly related to some strains observed in wild boars sampled in the same geographical area. The 3i subtype had never been detected previously in humans in Italy; it is likely that increased local circulation of 3i-like strains in wild boars may have increased the chance for their transmission to humans. Investigation of the possible risk factors for HEV infection highlighted consumption of raw/undercooked products from wild boars/pigs in three cases. However, in the remaining two cases, this source seems unlikely, and transmission might have occurred indirectly from contaminated sources, such as wastewater and home-grown vegetables. Further studies are needed to investigate if these latter sources may be more common than previously thought or may play a role in relation to specific HEV subtypes and/or only in rare and exceptional circumstances.