The world's first instance of rat hepatitis E virus infecting a human was discovered in a 56-year-old male resident of the city, the University of Hong Kong (HKU) revealed on Thursday night.
The case emerged when the patient -- who had undergone a liver transplant on May 14 last year at HKU’s teaching hospital Queen Mary and was on immunosuppressant drugs -- showed persistently abnormal liver function tests results. This indicated problems with his liver graft.
Further tests showed he was carrying a species of hepatitis virus that until then was known to be present only in animals such as rats and was “highly divergent” from the strain that affects humans.
The man lived in a housing estate “with evidence of rat infestation in the refuse bins outside his home”, HKU researchers who studied the case said.
“We postulate that contamination of food by infected rat droppings in the food supply is possible,” they said in a report, although they noted that the route of transmission of the virus remained unclear.
The man had noticed rodent droppings but had not seen rats inside his home, according to the report. Tests on rodent droppings, swab samples from the drain and floor from the refuse room, and even rats in the area, tested negative for rat hepatitis E.
But frozen samples from a rat collected by food and environmental hygiene authorities in the district in 2012 were found to have the virus.
The patient was treated with an oral medication known as ribavirin and is recovering.
Hong Kong has experienced rodent infestations during its hot and humid summers, and hygiene authorities have for the last 18 years produced a rodent infestation index on areas they manage.
Last year, the rodent infestation rate (RIR) for June to December for the city as a whole was 3.5%, down from 4% in the same period a year earlier. But officials admitted that the RIR might not fully reflect the situation in individual districts.
Before this case, there had been no previous evidence that rat hepatitis E, one of the variants of the virus that affects mammals, could be transmitted to humans.
Every year, the hepatitis E virus infects about 20 million people worldwide. It is known to be transmitted via food or water contaminated by faeces containing the pathogens. Patients have also got the virus from eating undercooked meat from infected animals and through blood transfusions from infected donors.
Symptoms of hepatitis E viral infection include fever, reduced appetite, abdominal pain and jaundice. In rare cases, it could lead to acute liver failure and death.
Details of the study, led by Professor Yuen Kwok-yung and Dr Siddharth Sridhar from the university’s department of microbiology, will be published in the medical journal Emerging Infectious Diseases in December.
HKU will hold a press briefing on Friday afternoon to reveal more about the case.
Earlier this summer, Hong Kong faced a rampant rodent problem, with control officers reporting double-digit growth in demand for their services over the past few months. Facebook posts from users in Tseung Kwan O, Ma On Shan and Ho Man Tin showed images of rats or mice caught on glue boards or scouting around packaged food in supermarket fridges.
