Hong Kong’s rat population could well sustain the hepatitis virus recently proved capable of jumping from rodents to people, a medical expert said following the report of the world’s second such human infection in the city.
About 1 per cent of rats carry the hepatitis E virus, according to studies in neighbouring cities, Dr Siddharth Sridhar, clinical assistant professor at the University of Hong Kong’s department of microbiology, said.
The latest rat-to-human infection was reported on Monday, and involved a 70-year-old Hong Kong woman. That came almost two months after another local resident was revealed as the first in the city, and also thought to be the first known case in the world.
Both patients lived in Wong Tai Sin district and were infected last year.
“As rats have a high reproductive rate and there are always non-immune young rats, the virus is probably stably maintained in rat populations,” said Sridhar, who was involved in investigation of the two cases.
Citing previous studies in Shenzhen and other parts of Guangdong province, he said about one in every 100 rats carried the hepatitis E virus at any one time.
“It is reasonable to assume that the situation in Hong Kong is similar,” he said, though he added the virus’ prevalence among local rats was not precisely known.
The rat hepatitis E virus was first discovered in 2010, and circulates among house rats and sewer rats. It is distantly related to the human variants of the virus.
While both affected Hongkongers lived in Wong Tai Sin, more data from local rats would be needed to determine if the virus is more prevalent among rodents in the area, the doctor said.
He added that he saw no need in a citywide screening for the virus among rats.
According to data from the Food and Environmental Hygiene Department, the rodent infestation index in Wong Tai Sin was 1 per cent last year, lower than an overall figure of 3.5 per cent for the city.
Sridhar said knowing how prevalent the virus is among local rats would not on its own help researchers understand the reasons behind the human infections.
“How did the virus get into patients’ food or their systems is something that is still unclear,” he said.
“But [screening] does tell us what we need to do in the future in terms of rodent control.”
Most people infected with hepatitis E suffer no symptoms, or only mild ones. But some sufferers have abdominal pain, nausea, tea-coloured urine and diarrhoea.
A spokesman for the department 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 examination, he said, noting that before that researchers were not told where each sample came from.
Referring to the two reported patients, Sridhar said it was likely they were infected by eating food contaminated by infected rats. But it would be hard to find what food it was.