"Previous laboratory experiments have found that rat hepatitis E virus can not be transmitted to monkeys, and human hepatitis A virus can not be transmitted to rats", said Dr. Siddharth Sridhar, clinical assistant professor at the University of Hong Kong, according to CNN.
Doctors discovered the man was carrying the animal strain after he experienced abnormal liver function after a liver transplant.
Yuen pointed out that this study proved for the first time in the world that rat HEV could infect humans and highlighted the importance for rodent control measures as human infection by rat HEV had never been documented previously.
"We don't know if in future there will be a serious outbreak of the rat hepatitis E virus in Hong Kong", he said.
The full extent of the rat-specific version of hepatitis E is not fully known, aside from what was observed in the patient.
Further researches showed signs of an immune response to hepatitis, which serves as a major cause of viral hepatitis in humans worldwide, he said. The virus can cause deadly liver failure in humans.
Researchers from the University of Hong Kong suspect he became infected after eating food that was contaminated by infected rat droppings.
Hepatitis results in inflammation of the liver caused by various viruses. Doctors later found that he had a strain of hepatitis that was "highly divergent" from other strains found in humans, the BBC reports.
The virus is known to be carried by pigs, wild boar, deer, rabbits and rats but does not make them ill. To the transplanted organ, "stuck", the man used immunosuppressants.
Officials said the man's health improved after the condition was identified and he received antiviral treatment.
The human version of hepatitis E affects 20 million people globally each year, according to the World Health Organization.
Until now, it has been widely accepted that hepatitis E can not be transferred from rats to humans.
He explained that, when it comes to disease susceptibility, monkeys closely resembled humans, but the risk of rat hepatitis E affecting humans was underestimated.
It has prompted fears that the virus could signal an impending outbreak in the Chinese city, which has been plagued by rodent problems due to long hot spells this summer.
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