Hepatitis E virus (HEV) infections constitute a significant health problem worldwide, with 4 major genotypes (HEV1-HEV4) being implicated in human infection/disease. HEV3 and HEV4 are considered zoonotic genotypes as they infect both humans and animals and are responsible of autochthonous human hepatitis E cases in industrialized countries. In recent years, highly genetically divergent hepeviruses (rat HEV: RHEV) recognizing rats as primary animal reservoir, were identified in both immunocompetent and immunosuppressed patients with acute or chronic hepatitis.
In this framework, Palombieri and collaborators investigated the epidemiology and the genetic variability of RHEV in Italy, assessing sewage samples from fourteen wastewaters treatment plants (WWTPs) distributed across the Abruzzo region (Southern Italy), a geographic area considered a hot spot for HEV infection in Italy.
The 155 raw sewage samples collected during a 30-months period in 2019-2022 were tested using a pan-hepevirus RT-PCR. On direct sequence analysis, 68 (43.8%) specimens displayed the high genetic relatedness with RHEV sequences currently available on GenBank database. Based on the inspection of the phylogenetic tree, the Italian RHEV strains grouped in different genetic clusters with a clear geographic/WWTP-related pattern, a finding that would be consistent with the persistence of the same strain within local rat populations. Intriguingly, a RHEV strain detected in this study formed a well-separated subclade with a human RHEV recently identified in a kidney-transplanted patient with cirrhosis in France.
Authors of this study hypothesized that the presence of RHEV in raw wastewater could be accounted for by direct fecal contamination of untreated water by the rodents inhabiting the sewage system. Although close contact with rats or with rat fecal droppings could be the primary transmission route for humans, the source of RHEV infection for the 21 patients affected by rat hepatitis remains still undetermined. The occurrence of RHEV in urban wastewater highlighted in this study raises the question as to whether contaminated surface waters can be responsible for waterborne transmission.
To read this study published in Microbiology Spectrum on 25 October 2023: DOI: 10.1128/spectrum.02675-23
