Until now, there had been no evidence the virus could jump from rats to humans, researchers said. In a statement, they added: "This study conclusively proves for the first time in the world that rat HEV can infect humans to cause clinical infection."
The university said rat HEV is only distantly related to strains of hepatitis E which more commonly affect humans.
The virus causes hepatitis, an inflammation of the liver, and cannot be cured but usually heals on its own.
According to a report in the South China Morning Post, the man lived on the Choi Wan housing estate, where there were signs of rat infestation. Rodent problems have worsened in Hong Kong recently because of a sustained spell of hot and humid weather.
Experts suspect the man ate something which had touched rat faeces, allowing the virus to enter his body when he ate. The man is now recovering after being treated in hospital, the Morning Post added.
Hepatitis E is usually spread through contaminated drinking water and causes fever, vomiting and jaundice, in which the skin and eyes turn a shade of yellow. It can cause liver failure, which can be deadly if not treated by doctors.
The human version of the hepatitis E virus affects 20 million people globally each year, according to the World Health Organisation.
There are four other types of hepatitis known to affect humans – A, B, C and D – and most can be spread by human bodily fluids and faeces. Hepatitis E is a major health threat in developing countries in Africa and Asia and in the past has been contracted from eating undercooked pork and deer meat.
Research published in the journal Emerging Infectious Diseases in 2012 said there are types of HEV which could be caught from pigs, boars, deer, mongoose, rabbits and cattle, but at the time did not think it could be caught from rats or chickens.
