The recent spread of eating habits linked to the consumption of raw or undercooked fish and cephalopods has increased the risk of exposure to fish-borne parasites. Among these habits, the consumption of sushi (imported from Japan), poke (from Hawaii) or ceviche (from Peru) is increasingly popular.
We must not take the matter lightly. Every year, almost one in ten people get sick from eating contaminated food. Specifically, the World Health Organization estimates that some 56 million cases of parasitic infections associated with the consumption of fish products occur annually.
Among fish-borne parasites, there are three major groups of helminths that parasitize humans: flatworms (flatworms), spiny-headed worms (acanthocephali), and roundworms (nematodes).
Of all the diseases caused by fish helminths, opisthorchids, a family of flatworms, are the most frequently diagnosed, but their spread occurs mainly in East and Southeast Asia. Hence, the global repercussion is less than that caused by some nematodes of the Anisakidae family, particularly species of the Anisakis, Pseudoterranova and Contracaecum genera, which concentrate much of the world's medical and economic concern.
Specifically, anisakiasis, caused by larvae of nematodes belonging to the genus Anisakis, is considered the main threat to human health. Every year, on all continents, countless cases in humans are described, related, in part, to the boom in the consumption of certain products such as sushi or sashimi.
Only in Japan, where it is traditional and common to eat these dishes made with raw fish and shellfish, the average annual incidence of anisakiasis exceeds 7,000 clinical cases.
Today, anisakiasis is an emerging global human health problem and is also of economic concern, due to the potential negative effects on consumer confidence and trade problems associated with infested seafood.
It can be avoided? The answer is to understand the life cycle of the parasite.
The genus Anisakis comprises nine species, three of which (Anisakis simplex sensu stricto, Anisakis pegreffii, and Anisakis physeteris) have been confirmed as zoonotic pathogens of humans. These nematodes parasitize a wide range of marine organisms and their life cycle includes dolphins, whales, seals, and other marine mammals as final hosts, as well as fish and cephalopods as intermediate hosts.
Adult worms are found in the stomach mucosa of marine mammals. The parasite's eggs are expelled through the feces and embryonate in seawater. There, crustaceans (krill) become infected with larval stages of nematodes. When crustaceans are preyed on by fish or squid, the third instar larvae infect the viscera of predators and encyst on organ surfaces and eventually on the musculature.
And that's where we come in: humans can become accidental hosts by eating cephalopods or fish that are raw or undercooked, and even smoked, salted or in brine, containing third instar Anisakis larvae. Once ingested, the larvae settle in the stomach and small intestine of humans.
In humans, the parasite cannot reproduce, but it can survive for a short time and cause anisakiasis, which ranges from mild to severe depending on the infected person. This disease can manifest gastric, intestinal and ectopic disorders, abdominal symptoms, allergic manifestations and even anaphylactic shock.
The most typical symptoms of gastric anisakiasis include abdominal pain, nausea, and vomiting within a few hours of ingesting the larvae. Small bowel involvement is less common, but when it occurs it can lead to an inflammatory mass and subacute, Crohn's-like symptoms that develop 1 to 2 weeks later.
In addition, some workers in the fishing industry, cooks, and other professionals who regularly deal with fish may suffer from occupational allergic anisakiasis. In this case, it is not necessary to ingest larvae or oral exposure to the parasite for the disease to manifest: sensitization occurs through Anisakis proteins that come into contact with the skin or the respiratory tract.
The general prognosis for anisakiasis is positive. Most infections are self-limiting and usually resolve spontaneously after several weeks. Transmission from person to person is not feasible.
Salmon, tuna, squid, cod, hake, mackerel, horse mackerel, blue whiting, sardines and anchovies (anchovies) are among the species that are most frequently parasitized.
More than 90% of anisakiasis cases worldwide are reported in Japan, and most of the remaining 10% are reported in countries such as Spain, Italy, USA (Hawaii), the Netherlands, and Germany. These are regions where, by tradition, we eat raw or undercooked fish dishes, such as sushi and sashimi, ceviche and carpaccio, anchovies in vinegar or pickle, Hawaiian-style salmon lomi-lomi and salted herring. .
Can anisakiasis be avoided? Preventive measures are essential to control the disease, and some help to minimize the problem. For starters, while the worms can withstand pickling and smoking, cooking at temperatures above 150°F destroys the larvae. A temperature that is achieved by preparing them fried, baked or grilled.
The Spanish Agency for Food Safety and Nutrition reports that traditional preparations of fishery products (cooking, frying, baking, grilling) inactivate the parasite, since they allow temperatures to reach 60°C throughout the piece for at least one minute.
Semi-preserves such as anchovies and traditionally salted dried fish, such as cod or mojamas, involve processes that kill the parasite.
Another common solution involves freezing, since the larvae are destroyed by being subjected to -20 ºC for 7 days or to -35 ºC for more than 15 hours. If the refrigerator has less than 3 stars, it is prudent to buy the frozen fish. In some countries, to increase consumer food safety, the same prepared commercial sushi is frozen before going on sale.
In addition, to avoid anisakiasis, it is advisable to carry out a visual inspection of the liver, gonads and visceral cavity of eviscerated fish, as well as a candling of fish fillets. European and Spanish legislation requires that fishery products are not offered for sale with visible parasites. It is advisable to buy clean fish without guts.
Oysters, mussels, clams, clams and other bivalve molluscs, as well as inland water fish (rivers, lakes, swamps...) and freshwater fish farms, such as trout and carp, do not require freezing.
Similarly, fish from aquaculture may be exempted from mandatory freezing, as long as they have been reared from captive-bred embryos, fed zoonotic parasite-free feed, and maintained in an environment free of viable parasites.
This article was originally published on The Conversation.
