Towards a better characterization of rat HEV transmissible to humans

Dr. Sylvain Beorchia | May 9, 2025 (JIM/J.JHEP)

The hepatitis E virus belongs to the Hepeviridae family, specifically to the Orthohepevirus genus, which is divided into several species (A, B, C, D). Humans are generally infected by viruses belonging to the Orthohepevirus A species (Paslahepevirus Balayani, comprising eight genotypes), which affects more than 20 million people worldwide and causes up to 70,000 deaths per year.

Rats can be infected by another species called Orthohepevirus C (including the genotype C1, Piscihepevirus Rocahepevirus ratti, or rat VHE, rVHE), a relatively recently discovered virus found worldwide in various species of rats. In 2018, rVHE was found to be capable of crossing species barriers to infect humans, causing acute infections that resolve spontaneously, as well as severe cases of fatal acute liver failure and persistent infections in immunocompromised individuals.

This rat hepatitis E virus is an emerging cause of acute hepatitis worldwide. The limited number of reported rHEV cases may be due to the lack of an appropriate method for standardized and sensitive molecular diagnosis, which explains the uncertainty surrounding previously analyzed clinical cases.

The development of a molecular diagnostic algorithm

Caballero-Gómez et al. established a molecular diagnostic approach sensitive for detecting rVHE in various rodent cohorts, as well as in 562 patients with acute hepatitis of unknown origin. The algorithm developed showed that 17.5% of the 103 rodents in a validation cohort were infected with rVHE. 

Among the clinical cohort of 562 patients with acute hepatitis of unknown origin, rVHE infections were initially detected by RT-PCR in 51 subjects, 8 of whom were confirmed by sequencing. This corresponds to a prevalence of 1.4% of cases.

Four patients developed severe hepatitis requiring hospitalization, one of whom died. The authors also report cases of acute kidney injury and acute pancreatitis, which are considered to be suspected extrahepatic manifestations. 

The epidemiology of the virus remains to be clarified

The identification of rVHE as a public health issue was made possible by the development of a highly effective molecular diagnostic algorithm. This methodological approach « One Health » enabled the identification and evaluation of molecular tests for screening for HEV in rats and subsequently in humans, with full molecular confirmation of rHEV infection. 

The rVHE strains identified in humans were likely transmitted through direct or indirect contact with infected rodents. Similar cases have been identified in Hong Kong, supporting the hypothesis of regional transmission cycles, while the cases reported in Canada and France have an uncertain geographical origin.

The exact global distribution of rVHE in humans remains largely unknown, and future studies will need to conduct more precise phylogeographic analyses and identify potential sources of transmission. The relatively frequent detection of rVHE suggests that its transmission to humans is neither rare nor random, despite the limited data available on the incidence of infection with this virus in humans.

It shows a close genetic relationship (nucleotide identity of 82% to 99.5%) with the one previously detected in Spanish rats. 

Clinical similarities between classical HEV and rat HEV

The clinical course observed in the rVHE cases identified in this study is consistent with that reported in previous studies, reinforcing the role of this virus as an emerging cause of acute hepatitis with extrahepatic manifestations. Given the similarity between rVHE and classical HEV, the clinical course of infections caused by the two viruses is likely comparable.

In Asia, rHEV infection follows a similar course to that of HEV in terms of liver damage and mortality rates. However, this finding cannot be extrapolated to other regions due to significant differences in the epidemiology of the 8 HEV genotypes. Further studies should therefore be conducted to elucidate the potential differences between the clinical course of rVHE and HEV in the European population.

The risk factors for human infection with this new virus are not well understood. While rats serve as both an evolutionary reservoir and a zoonotic source of infection, the routes of exposure (direct, through contaminated food, or through ingestion of rodent feces) require further study. Finally, the same group also reported the detection of rVHE in Spanish pigs. 

The limitations of this new RT-PCR 

Several limitations must be taken into account. Using an ALAT threshold of 3N instead of the 10N typically required to diagnose acute hepatitis could lead to selection bias toward patients with other conditions that cause a mild, chronic elevation in transaminases, such as NASLD and/or alcohol-related liver disease.

In addition, 4 out of 8 positive patients required hospitalization, which contrasts with data on acute and chronic HEV cases. Furthermore, no information is provided on how autoimmune hepatitis or drug-induced liver injury was ruled out. It would also be helpful to know whether a liver biopsy was performed in all cases of HEV infection in rats.

Despite the availability of a few automated tests and the establishment of an international standard by the WHO, many centers still use in-house techniques with relatively low sensitivity. There is a lack of information regarding the HEV RNA test used and its reproducibility on separate samples from subjects who are positive for this emerging virus.

Evaluating rVHE RT-PCR in a control group consisting of patients without acute hepatitis or with acute hepatitis of clearly defined causes could also help confirm the results. Finally, it should be noted that there was a lack of medium- and long-term microbiological follow-up for certain patients, particularly those with cancer, to detect chronic infection.

All of this data underscores the need to improve Sanger sequencing protocols for this emerging virus and to develop advanced sequencing methods for whole rVHE genomes, for example by using next-generation sequencing (NGS) techniques.

Inconclusive anti-rVHE serology

Consistent with other studies, these results highlight the complexity of detecting antibodies in human infections with rVHE. The timing of the test relative to the infection is an important factor to consider in explaining the low viral load observed in this study. Thus, in human cases of Paslahepevirus infection, the viral load often peaks before the onset of hepatitis symptoms.

It is therefore possible that the viral load had already begun to decline at the time of sampling, while antibodies had already formed. In addition to molecular detection, this study aims to shed new light on the serology of rVHE, although the results remain inconclusive for IgM and IgG.

It is therefore possible that the viral load had already begun to decline at the time of sampling, while antibodies had already formed. In addition to molecular detection, this study aims to shed new light on the serology of rVHE, although the results remain inconclusive for IgM and IgG.

In conclusion, rVHE is an underdiagnosed cause of acute hepatitis. Infection with this virus, which is closely related to known strains of classical HEV, should be considered as a differential diagnosis in all cases of undetermined hepatitis.

Thanks to the development of a sensitive molecular diagnostic algorithm, rVHE has been identified in rodent reservoirs and human patients, revealing great diversity and close phylogenetic relationships among the strains.

These findings also highlight the need to improve sequencing techniques, standardize PCR-based molecular diagnostics, and expand geographic surveys. This would improve diagnostic accuracy and our understanding of the epidemiology of this new zoonosis capable of infecting humans in Europe. 

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References

Caballero-Gómez J, Casares-Jiménez M, Gallo-Marín M, et al ; GEHEP-014 Study Group. Rat hepatitis E virus as an aetiological agent of acute hepatitis of unknown origin. J Hepatol. 2025 Feb 26:S0168-8278(25)00136-9. doi: 10.1016/j.jhep.2025.02.027.