2023-04-30 08:00:00
DIncreasingly, the consumption of raw fish, squid and octopus is growing, while sushi, Hawaiian poke and ceviche are already on our tables. However, these culinary specialties are not without health risks: they can expose you to parasites carried when the food is raw or undercooked. Salmon, tuna, squid, cod, hake, mackerel, horse mackerel, blue whiting, sardines and anchovies are among the most frequently parasitized species.
The problem is not to be taken lightly. Every year in the world, almost one person in ten is affected by anisakiasis, a parasitic infection caused by larvae of nematodes belonging to the genus Anisakis, following consuming a contaminated dish. Specifically, the World Health Organization estimates that 56 million cases of anisakiasis per year are associated with the consumption of fish products.
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Over 90% of anisakiasis cases are reported in Japan (the annual incidence of anisakiasis there exceeds 7,000 clinical cases), and most of the remaining 10% in countries such as Spain, Italy , the United States (Hawaii), the Netherlands and Germany… In short, regions where people traditionally eat raw or undercooked fish dishes, such as ceviche and carpaccio, marinated or pickled anchovies , Hawaiian-style lomi-lomi salmon and salted herring.
Anisakiasis has therefore become an emerging health problem worldwide. It is also an economic concern, due to consumer mistrust and trade problems associated with infested fish products.
Three major groups of parasitic worms
Among the parasites transmitted by fish, three large groups can infect humans: flatworms, spiny-headed worms (acanthocephala), roundworms (nematodes). Opisthorchid infections (a family of flatworms) are most commonly diagnosed, but it is found mainly in East and Southeast Asia. Its impact at the global level is therefore less than that of certain nematodes of the family of Anisakidae.
The species of the genera Anisakis, Pseudoterranova et Contra-blind are thus at the heart of a large number of medical concerns.
The life cycle of the parasite
How do you get anisakiasis? The answer lies in understanding the life cycle of the parasite. Genre Anisakis includes nine species, three of which (A. simplex, A. pegreffii et A. physeteris) have been confirmed as zoonotic pathogens for humans. These nematodes parasitize a wide range of marine organisms and their life cycle includes dolphins, whales, seals and other mammals as final hosts, as well as fish and cephalopods (octopuses, etc.) in as intermediate hosts.
Adult worms are initially found in the stomach lining of marine mammals, where they reproduce. The parasite eggs are then expelled by the animal’s faeces and will develop in seawater. Now in the form of larvae, the nematodes will infect crustaceans (krill). When the latter are the prey of fish or squid, the parasite (still in the form of a larva, but in the third stage) can then reach the intestines of the predator and encyst on the surface of its organs, then in its musculature.
It is then that man can become an accidental host of the parasite, by eating cephalopods or raw or undercooked fish, or even smoked, salted or pickled fish, which contain the larvae ofAnisakis (of the third stage). Once ingested, the larvae settle in the stomach and small intestine.
Symptoms of anisakiasis
Once in the human body, the parasite is trapped. It can no longer reproduce, but can survive for a short time and cause anisakiasis. The disease, which varies from mild to severe depending on the person infected, can manifest itself in gastric, intestinal and abdominal disorders, allergies (14 allergens have been described) and even anaphylactic shock. Rare phenomenon: the infection can settle outside the gastrointestinal tract.
The most typical symptoms of gastric anisakiasis include abdominal pain, nausea, and vomiting within hours of ingesting the larvae. Involvement of the small intestine is less common, but when it occurs it can lead to massive inflammation and subacute symptoms, similar to those of Crohn’s disease, which develop one to two weeks later.
READ ALSO“Your health is well and truly on your plate” In addition, some workers in the fishing industry, cooks, and other professionals who regularly handle fish may suffer from occupational allergic anisakiasis. In this case, the ingestion of larvae or oral exposure to the parasite is not necessary for the disease to manifest itself: sensitization takes place via the proteins ofAnisakis that come into contact with their skin or respiratory tract.
The overall prognosis for anisakiasis is positive: most infections are limited and disappear spontaneously following several weeks. Person-to-person transmission is not possible.
How to get rid of the parasite
Can you avoid getting anisakiasis? Preventive measures are essential to control the disease. First, although the worms are resistant to pickling and smoking, cooking at temperatures above 63°C destroys the larvae. A temperature reached by frying, baking or grilling them.
In Spain, which is one of the European countries most affected, the Agency for Food Safety and Nutrition reports that traditional preparations of fish products (frying, baking, grilling) inactivate the parasite, as they allow reach a temperature of 60°C for at least one minute.
Semi-preserved (in airtight containers and pasteurized, salted, dried, etc.), as practiced on anchovies or cod involve processes that kill the parasite.
READ ALSOThe belly, our second brainAnother common solution is freezing, because the larvae are destroyed when subjected to a temperature of -20°C for seven days, or -35°C for more than 15 hours. In some countries, to increase consumer food safety, commercially prepared sushi is even frozen before being offered for sale.
In addition, visual inspection of the liver, gonads and visceral cavity of gutted fish, as well as inspection of fish fillets, is preferable. European legislation requires that fish products showing visible parasites should not be offered for sale. It is advisable to buy clean and gutted fish.
Not all seafood is subject to the same restrictions. No need for freezing for oysters, mussels, clams, and in general for shellfish and bivalve molluscs, as well as fish from inland waters (rivers, lakes, marshes, etc.) and freshwater fish farms, such as trout and carp.
Similarly, fish from aquaculture may be exempted from the freezing requirement, provided that they have been bred from embryos obtained in captivity, that they have been fed with feed free of zoonotic parasites and that they have been maintained in an environment free of viable parasites.
* Raúl Rivas González is a member of the Spanish Society of Microbiology and Professor of Microbiology – University of Salamanca.
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