Sushi worms on the climb in Japan - but expert says ‘no need to panic’

Sushi worms on the climb in Japan - but expert says ‘no need to panic’

SINGAPORE: A local food safety expert on Wednesday (May 17) cautioned against overreaction but called for added deterrence, in light of warnings from both Japanese and Western authorities last week on parasitic infections caused by eating raw seafood.

Japan’s health ministry released figures showing a spike in reported infections by the Anisakis worm, from four in 2004 to 126 last year. And doctors in Portugal filed a medical report linking the growing recognition of Anisakis cases in the West with the increasing popularity of Japanese raw seafood delicacies like sushi and sashimi.

The doctors had found Anisakis larvae - up to 3cm long and 5mm wide - in the gut lining of a Portuguese man after he consumed sashimi at a Japanese restaurant.

sushi worms in gut
An Anisakis parasite attached to the gut lining of a man, as seen in an endoscopy (Photo: BMJ Case Reports)

This particular worm infects crustaceans, fish, squid and marine mammals, said Associate Professor Kevin Tan of National University of Singapore’s Department of Microbiology and Immunology.

“The larvae of the parasite can be found in the muscle tissue of fish. Humans can be incidentally infected through consumption of raw or undercooked seafood containing the larvae of the worm,” he explained.

“The ensuing disease is known as anisakiasis. The signs and symptoms of anisakiasis are abdominal pain, nausea, vomiting, abdominal swelling, diarrhoea, and mild fever.”

Said Professor William Chen, Director of Nanyang Technological University’s Food Science and Technology Programme: “This parasite will not be present in all fish. But consumers of a diet and lifestyle with lots of raw fish, for example in sushi and sashimi, tend to have a higher risk of infection.”

“This is not something new,” he added, noting that anisakiasis cases have been reported since the 1950s. “There is no need to panic. But prevention is critical.”


Typical preventive measures to kill parasitic larvae include deep freezing - as soon as the fish is caught - and cooking at high temperatures, although exact guidelines differ across countries.

In Japan, consumers are recommended to keep fish frozen below minus 20 degrees Celsius for at least a day, or to heat it for at least a minute at over 60 degrees.

The US Food and Drug Administration (FDA) on the other hand advises freezing fish at either minus 20 degrees for seven days, or minus 35 degrees until solid and then storing at minus 20 degrees for 24 hours.

In Singapore’s case, fish must be frozen at minus 18 degrees or below, and no higher than minus 12 degrees.

“There are no specific conditions,” Prof Chen admitted. “It also depends on the number of worms present in the fish, or the thickness of the fish. All this is a guideline - to make sure all parasites are properly killed, there is no harm in prolonging freezing.”

He said the supplier accreditation scheme by Singapore’s Agri-Food and Veterinary Authority (AVA) - all food entering the country must originate from approved sources - comes with the necessary preventive measures which should give consumers confidence in local food quality.

But Prof Chen acknowledged that consumer awareness and action was a potentially “tricky” matter.

“It would be cumbersome to always not trust the food you are eating, to always ask questions etc.,” he pointed out. “But perhaps Government agencies can provide information on the source or supplier of Japanese restaurants here. I think that would give people a good gauge of what they’re in for.”