Anisakis infections from raw fish on rise, health ministry warns

Beware, sushi and sashimi lovers: If you feel a sharp pain in your stomach after enjoying a bowl of raw seafood, you might have succumbed to the perils of the parasitic worm Anisakis.

The Health, Labor and Welfare Ministry has issued an official warning on the rapidly growing number of Anisakis infections linked to eating raw or undercooked fish.

Larvae of the white, string-like parasite are about 5 mm wide and up to 3 cm long. They are often found in species like mackerel, Japanese horse mackerel, salmon, saury, sardines and squid.

After infecting the intestines of their hosts, they move into their muscles when the hosts die.

According to the ministry, the reported number of Anisakis infections surged to 126 in 2016 from 79 in 2013. There were only four cases reported in 2004.

But Haruka Igarashi of the health ministry’s department of environmental health and food safety said that the rise in reported Anisakis infections in recent years might be in part due to increased public awareness.

Symptoms typically include severe abdominal pain, nausea, vomiting and low-grade fever and may develop within an hour or two weeks after consuming infected fish.

According to a 2008 study published in the U.S. journal Clinical Microbiology Reviews, Anisakis can also induce allergic reactions and immune hypersensitivity.

The ministry urges consumers to keep the fish frozen below minus 20 degrees for at least a day, or heat it for at least for a minute in temperatures exceeding 60 degrees, which should kill the larvae.

Keiko Saito, another ministry official, warned consumers to inspect seafood carefully before buying or eating the fish.

“We suggest that consumers who buy whole raw fish remove the internal organs, where the larvae commonly are,” she said. “It is highly likely there might be a plenty of them in the intestines.”

Experts also say that people with severe pain should go see a doctor and have the parasite removed using endoscopes.

Japanese comedian Tomoharu Shoji, revealed on the Fuji TV program “Tokudane” on Wednesday that he contracted the parasite last summer. Shoji, 41, said he had been diagnosed with Anisakis after eating raw salmon and salmon roe with rice while on location.

He said he started feeling strong, persistent pain in the middle of the night that was misdiagnosed by the first doctor as stomach spasms. Later, it turned out that he had eaten seafood infected with eight larvae that had perforated his stomach and caused it to bleed.

Yaeko Takahashi of the Tokyo Metropolitan Government’s bureau of social welfare and public health said the trend has been spiking in the capital.

“The number rises every year,” she said, adding that more cases have been detected recently by endoscopy at hospitals. While greater public awareness of Anisakis has led to more reported cases, many more escape undetected, she said.

Takahashi said that both consumers and food businesses should be more careful handling seafood.

“There are business operators (serving or transporting fish) who do not preserve or prepare the fish appropriately,” she said. “Given the growing number of outbreaks, it is likely that there are many operators not doing their job properly.”

Anisakis infections were first reported in the Netherlands in the 1950s and are believed have been caused by larvae in herring.

The larvae have so far been found in European countries and the United States, with a majority of the cases attributed to consumption of Pacific salmon.