The researchers said on Wednesday they found a second patient in Hong Kong who has contracted a rat-hepatitis virus in what appears to be the first known human cases in the world.
The find surprised the researchers, although it was not immediately clear whether there were significant implications for human health.
"Because the rat … virus is very different from human pressure, people think they will not be able to jump on people," said Sidartat Sidar, one of the main researchers at the Hong Kong University. "This was a clinical discovery."
The first case came out in September. The researchers confirmed that a 56-year-old man had hepatitis E, previously known only to rats in Vietnam.
The second case was detected by blood samples from more than 70 patients with hepatitis E, who were tested.
An 70-year-old woman with a compromised immune system was found to be infected with a hepatitis virus, the Hong Kong Ministry of Health announced on Wednesday via an email response to questions.
She was admitted to hospital in May 2017 with abdominal pain, headache, anorexia, and other symptoms. The blood samples collected from her at that time were recently positive.
The two patients were hospitalized for only a few weeks and lived in three miles (two miles) from each other.
"They form a cluster – they are connected with time and space," Shridar said. The types found in patients "are incredibly similar."
However, the Department of Health said: "The sources and ways of infection of these two cases can not be determined".
Other types of hepatitis E are often transmitted by humans through contaminated water, especially in East and South Asia. In China, many have been affected after eating pork and pork. China has developed a licensed hepatitis E vaccine, but it is not yet available outside the country.