Fresh pig liver may be one of the sources in the spread of the food-borne hepatitis E virus in Hong Kong, the Centre for Food Safety warned yesterday.

As a result of the rising trend in cases, the center obtained 100 liver samples from pigs slaughtered in Sheung Shui Slaughterhouse from mid-January to May 2009, Hong Kong's The Standard.

None of the 49 liver samples from porker pigs (around six months old) was found to be positive for HEV but 16 out of 51 samples from roaster pigs (roughly four months old) were found to be positive.

Center consultant Ho Yuk-yin said the study shows that pigs may be one of the sources of local human hepatitis E cases, though there are other potential sources such as contaminated water and food, in particular raw or undercooked shellfish.

"The local cases were all sporadic. As the incubation period of HEV varies from two to nine weeks, it is difficult to determine the exact source of infection for individual cases," Mr Ho said.

Scientific officer Chong Tsz-kit said those infected may have symptoms including fever, malaise, anorexia, nausea, abdominal pain, jaundice and tea-colored urine.

"It is usually a mild disease and resolves in two weeks," he said.

"However, there may be severe complications in high-risk groups such as pregnant women, patients with chronic liver disease and the elderly.

"No commercial vaccine for hepatitis E is available at present."

Mr Chong said a number of overseas studies claim that HEV is more commonly detected in pigs, especially those aged four months or younger, and they may be a potential source of human cases. The results of the center study echo those conducted overseas.

"The public and the trade should cook pork and offal thoroughly, especially when cooking in a hotpot or with congee," Mr Chong said.

"Sliced pig liver should be boiled at 100 degrees Celsius or stir-fried for at least three to five minutes depending on thickness and quantity.

"For shellfish, the public should heat it to an internal temperature of 90 degrees Celsius for at least 90 seconds. Shellfish should be boiled at 100 degrees Celsius until their shells open and afterwards for another three to five minutes."

Mr Chong also reminded the public to practice good personal and food hygiene.