The disease was found in a 56-year-old man who repeatedly produced abnormal liver function tests following his liver transplant. However, there was "evidence of rat infestation in the refuse bins outside his home", according to the research team.
His colleague, Professor Yuen Kwok-yung, a microbiologist at HKU, added: "We don't know if in future there will be a serious outbreak of the rat Hepatitis E virus in Hong Kong".
Martin Hibberd, professor in emerging infectious disease at the London School of Hygiene and Tropical Medicine said it is "highly unlikely" that the virus could have been transmitted between humans.
Researchers think the man may have been infected after eating food contaminated with rat droppings or by possibly being bitten by a rat.
Traditionally, the HEV is transmitted by the fecal-oral route, principally via contaminated water.
But, as of May 2018, there was not a US Centers for Disease Control and Prevention (CDC) approved hepatitis E vaccine. The man lives next to a trash chute, where conditions aren't hygienic, the Post said.
Hepatitis can be caused by various factors, including viruses or alcohol.
The World’s First Human Case of Rat Hepatitis E Was Detected in Hong Kong
The virus is known to be carried by pigs, wild boar, deer, rabbits and rats but does not make them ill.
Many people clearly have hepatitis, based on their symptoms, but they test negative on all the human strains known to exist, Adalja said.
The man is said to be recovering.
Symptoms of hepatitis E in humans include fever, fatigue, nausea and vomiting, jaundice, abdominal pain, joint pain and dark-colored urine.
A sustained period of hot and humid weather has caused rodent problems in Hong Kong to escalate.
"Infections that jump from animals to humans must be taken very seriously", Sridhar told The New York Times.
Cases of HEV typically present in one of two ways, either as large outbreaks and sporadic cases in areas where HEV is endemic (genotype 1) in Asia and Africa, (genotype 2) in Mexico and West Africa and (genotype 4) in Taiwan and China or as isolated cases in developed countries (genotype 3), reports the WHO.
The human version of hepatitis E is a liver disease that affects 20 million people globally each year, according to the World Health Organisation.
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