Letter to the Editor: Emergence of Zoonotic Rat Hepatitis E Virus Infection.

To the Editor:

We noted the identification of further rat hepatitis E virus (HEV) cases in humans in Hong Kong.( ) This emergence, infection of a Canadian United Nations worker in Africa,( ) and serological evidence of exposure in German foresters( ) and hospitalized Vietnamese patients( ) raises the question of how widespread rat HEV infection is globally.

Rat HEV (Orthohepevirus C or HEV‐C) is distinct from epidemic HEV strains circulating in Africa, Asia, and to zoonotic pig strains responsible for disease burden in industrialized countries (Orthohepevirus A or HEV‐A). In Europe, hepatitis E is not notifiable, and, until recently, lack of awareness by physicians and poorly standardized diagnostics led to underreporting. In 2019, the European Centre for Disease Prevention and Control developed guidance on HEV surveillance (data collection/reporting, case definitions, and testing)( ); this and other guidelines do not currently consider HEV‐C. Despite similar clinical presentation of HEV‐C and HEV‐A (acute and chronic), molecular assays used clinically and for blood donor screening do not detect HEV‐C. A commonly used anti‐immunoglobulin M (IgM) assay can detect anti‐HEV‐C antibodies; however, HEV‐A/HEV‐C‐discriminatory assays are unavailable. Of the 169 anti‐IgM‐positive patients, Sridhar et al. identified 5 HEV‐C1 and 82 HEV‐A RNA‐positive patients.( ) Is more data on the remaining 82 HEV‐IgM‐positive/RNA‐negative patients available? Could variability of HEV‐C strains contribute to missed cases? There is a need to develop specific molecular and serological assays and associated control materials for HEV‐C, to assess case frequency in previously healthy immunocompetent as well as immunosuppressed individuals and understand the risk to humans.

Zoonotic HEV‐A is transmitted primarily through consumption of contaminated meat. While Sridhar et al. mentioned the proximity of the HEV‐C‐infected patients to rat infestations and droppings, there was no discussion about possible transmission of HEV‐C by consumption of rat meat or contaminated meat products. More detailed epidemiological investigations (environmental risk factors, consumption habits, and water contamination) are needed to identify infection sources and transmission patterns.