Sushi and Sashimi Lovers, That Tingling on Your Tongue Might Be Bad for You

A very special feeling in your mouth: Since when has risking tapeworm infection been irresistibly alluring?

Sushi
Katerinina / Shutterstock

Since when has risking tapeworm infection been irresistibly alluring? Is willingness to risk parasite infestation really an admirable trait? It seems to be the thesis among sushi-eaters that derring-do at the dinner table will win them admiration, possibly among their lily-but-healthy-livered friends who wouldn’t touch uncooked animals with a sterilized barge pole.

Sushi originated in Japan around 1,600 years ago, it seems, before they knew better. In defense of the ancient islanders, the science of medicine would remain no better at identifying the origin of morbidity until modern times, and despite the information out there, raw fish dishes have become enormously popular almost worldwide, including in Israel. 

The catch is that while catching a parasite from your dinner is very rare, it happens.

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In 2017 Japan reported that in recent years there had been an explosion in infestation by the nematode worm called anisakis, and the figure doubled in 2018 to 468 cases. The cause is apparently that more seafood was being shipped around the country raw, rather than being transported deep-frozen. Japan’s National Institute of Infectious Diseases estimated the number of anisakis infections alone at 7,000 a year.

Climate change may be contributing its bit. In 2018, anisakis parasitization of skipjack tuna may have increased because of changes in seawater temperature, a health official told Asahi Shimbun.

Eggs of tapeworm Taenia
Kateryna Kon / Shutterstock.com

What are anisakis’ favorite fish? Among them, salmon, mackerel, and also bonito and squid. And crustaceans. All of which we like too. Where is the nematode’s larva hiding out for your delectation? In the fish’s internal organs, which most of us don’t eat, and in its muscles, which is the part we do eat.

Meanwhile, also in 2017, doctors in Portugal warned that the anisakis infection was spreading in the West too because of the increasing popularity of raw foods like sushi and sashimi.

Sometimes when you eat raw fish or squid, you can feel a tingling feeling in your mouth. That’s the worm crawling around in there, says the U.S. Centers for Disease Control and Prevention. You can remove it with your fingers or, if you’re dextrous, with your chopsticks.

The good news is that anisakis infestation passes within up to two weeks, but the bad news is that you may be in quite a bit of discomfort before it does. "Once inside the human body, the larvae can invade the gastrointestinal tract. Eventually, the parasite dies and produces an inflamed mass in the esophagus, stomach, or intestine," the CDC explains.

Diagnosis of anisakis is usually based on gastrointestinal distress ("abdominal pain, nausea, vomiting, abdominal distention, diarrhea, blood and mucus in stool, and mild fever" - CDC again) and the knowledge that you ate sushi.

Tapeworms, which can stretch to 25 meters in length, are also on the rise worldwide as the mania for raw flesh spreads. If it’s any comfort, however, most of the offending creatures aren’t anywhere near that long. You may not even realize you’re infected. Or you could develop pain, bloating, vomiting or an allergic reaction, see little segments of worm in your toilet bowl and, in very rare cases, develop an intestinal blockage, if the creature hijacking your intestinal tract is massive enough.

Some might argue there’s not a salmon roll in the world that’s worth that thought.

Anisakis in a blue whiting.
Gonzalo Jara / Shutterstock.com

Mind you, parasites can also infect you due to consumption of undercooked or raw flesh of quadrupeds, not only marine animals. Some of the most common tapeworms come from pork and beef that have not been cooked properly.

Fans of sushi argue for the delights of eating raw fish and contend that the fishy flesh has been zapped in some form that will save them from worms, bacteria and viruses. It may have; it may not – and deep-frozen fish may get infected by a whole new unpleasantness such as listeria orsalmonella bacteria.

Certainly, sushi, sashimi and carpaccio vendors can take measures to kill any eggs, larvae or parasites lurking in their offerings, including flash-freezing followed by deep-freezing, and looking very carefully and removing any that one sees by eye.

Sadly, there are no solid guidelines for how long a fish or crustacean must be frozen, or cooked, and at what temperatures, in order to eradicate 100 percent of parasites or their eggs or larvae. That depends on the type and number of worms present in the animal, its thickness, the parasite species and other factors. Catching a fish in the wild and throwing it into your freezer, or "searing” it, and then eating it uncooked or insuffuciently cooked is just asking for it.

Meanwhile, note this. In 2014 the United Nations issued a warning about proliferating cases of infection by a certain tapeworm that can infest the nervous system: Taenia saginata, which causes neurocysticercosis. Once mainly the province of the poor in the third world, this worm (commonly if inaccurately known as the beef tapeworm) been making inroads in European and American populations who dote on carpaccio or who don't cook their pork chop properly.

Sushi and sashimi and carpaccio is usually perfectly safe. But some isn’t. “I wouldn’t touch it, any raw fish or meat,” a parasitologist specializing in another parasitic horror, myxozoans – a microscopic parasitic jellyfish – told Haaretz earlier this year. They typically infect live sea creatures and, of course, are present in their raw flesh as well. Now there’s food for thought.