The population of Hong Kong mice able to maintain the hepatitis virus has recently been shown to be able to jump from rodents to humans, a medical expert said after reports of the world's second human infection in the city.
About 1 percent of mice carry the hepatitis E virus, according to research in neighboring cities, Dr. Siddharth Sridhar, assistant clinical professor at the University of Hong Kong's microbiology department, said.
The latest mouse-to-human infection was reported on Monday, and involved a 70-year-old Hong Kong woman. That happened almost two months after other locals were revealed as the first in the city, and also considered the first known case in the world.
Both patients lived in Wong Tai Sin district and were infected last year.
"Because mice have a high reproductive rate and there are always young mice that are not immune, this virus may be stable in the rat population," said Sridhar, who was involved in the investigation of two cases.
The world's second reported case of hepatitis in humans was found in Hong Kong
Citing previous research in Shenzhen and other parts of Guangdong province, he said about one in every 100 mice carried the hepatitis E virus at one time.
"It is reasonable to assume that the situation in Hong Kong is similar," he said, although he added that the prevalence of the virus among local mice is not known exactly.
Hepatitis E virus rats were first discovered in 2010, and circulated among home mice and sewage mice. This is far related to the human variant of the virus.
While the two affected Hong Kong residents live in Wong Tai Sin, more data from local mice will be needed to determine whether the virus is more common among mice in the area, doctors said.
He added that he did not see the need for screening across cities for viruses among mice.
According to data from the Food and Environmental Hygiene Department, the index of rat infestations in Wong Tai Sin was 1 percent last year, lower than the overall figure of 3.5 percent for cities.
How the virus enters the patient's food or their system is something that is still unclear
Dr. Siddharth Sridhar, HKU
Sridhar said knowing how prevalent the virus among local mice would not help researchers themselves understand the reasons behind human infection.
"How the virus enters the patient's food or their system is something that is still unclear," he said.
"But [screening] tell us what we need to do in the future in terms of rodent control. "
Most people infected with hepatitis E do not suffer from symptoms, or only mild symptoms. But some sufferers experience abdominal pain, nausea, tea-colored urine and diarrhea.
A department spokesman said it had sent rat carcasses collected in various districts to HKU for studies since 2008. Since the second case was reported, the department had sent samples from Wong Tai Sin for review, he said, noting that before that researchers were not told where each sample originated.
Referring to the two patients reported, Sridhar said the possibility of them being infected by eating food contaminated by infected mice. But it will be difficult to find what food it is.