In a follow-up to a report on the second known human case of rat hepatitis E (HEV), Hong Kong officials report:

Hong Kong/CIA
Hong Kong/CIA

The second patient was a 70-year-old retired female with underlying illnesses on immunosuppression. She had developed abdominal pain, headache, anorexia, malaise and palpitation since May 1, 2017, and was admitted to a public hospital on May 4, 2017. She was discharged on May 8, 2017 and had recovered. Her blood sample collected on May 5, 2017 tested positive for anti-HEV IgM antibody by the Public Health Laboratory Services Branch (PHLSB).

This follows the initial case reported in September in a  56-year-old retired male who underwent deceased donor liver transplant in a public hospital on May 14, 2017 and was put on immunosuppressants for anti-rejection prophylaxis. 

Human infection by rat HEV has not been reported previously.

To study if there were other cases in recent years, the Hong Kong Centers for Health Protection (CHP) provided 73 archived blood samples of patients with positive anti-HEV IgM antibody but negative for human HEV nucleic acid by molecular test to HKU for further testing. Retrospectively, HKU identified that a previously notified HEV case was caused by rat HEV and genetic sequencing results found that the viruses detected in the two cases were highly similar.

In addition, CHP’s epidemiological investigation revealed that the two cases had no travel history during the incubation period of usual HEV infection. They both resided in Wong Tai Sin District and their residence was about two kilometres apart. No other findings suggestive of epidemiological link between the cases were identified. The two patients could not recall having direct contact with rodents or their excreta, or noticed rodents in their residence. However, the first case recalled having seen suspected rodent excreta in his home. Based on the available epidemiological information so far, the sources and routes of infection of these two immunocompromised patients could not be determined.

The usual HEV causing human infection belongs to Orthohepevirus A (HEV-A). Apart from HEV-A, the Orthohepevirus genus also has three other species, namely, Orthohepevirus B that circulates in chickens, Orthohepevirus C (HEV-C) in rats and ferrets, and Orthohepevirus D in bats. HEV-C, also known as rat HEV, shares only 50% to 60% nucleotide identity with HEV-A.As there is substantial phylogenetic divergence between HEV-A and HEV-C, serologic and molecular tests for human HEV might miss HEV-C infection.

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The apparent clustering of the two cases back in 2017 is of concern and CHP will continue to closely monitor the situation. The most important preventive measures for the transmission of HEV are food and environmental hygiene, including rodent control.