The Anisakis , as such, is a parasite whose adult larva can be detected with the naked eye in the abdominal cavity of many fish that inhabit the sea. Their approximate size is variable, but their length oscillates between the two and the three centimeters, and they have a filiform aspect of a rosy white color. It belongs to the family of so-called cylindrical worms, whose adult form inhabits large marine mammals.
Of all the diseases that can be contracted from marine foods, the main parasitoses that affect the western man are those of the family Anisakis. However, the human is not a suitable host for this parasite, so it does not usually complete its life cycle in the human species, not being able to develop to reach adulthood. This usually causes them to be expelled or die in a variable time period between hours and 2 to 3 weeks.
Where is the Anisakis?
Anisakis is a complex parasite, and requires a biological cycle for its reproduction. The adult parasite is usually found in the stomach of a large variety of marine mammals (seals, sea lions ...) including cetaceans (whales, dolphins, orcas ...), that is, the definitive host. In the stomachs of these mammals, the larva reaches adulthood and sexual maturity, so that the fertilized eggs are expelled into the sea through the digestive tract through the feces of the host. The eggs harbor the larva in its initial state. This larva, to reach the necessary maturity before parasitizing other fish, passes through other intermediary hosts (eupases or tiny crustaceans of the placnton). Fish and marine mammals acquire parasitization by feeding on plankton or by eating other previously contaminated fish. These fish and cephalopods thus host the third larval stage or L3 which is that which affects the human and which we know as Anisakis .
Which species may contain Anisakis larvae?
Any marine fish is susceptible to being infected with larvae of anisákidos. Many of them are of commercial importance, such as herring, sardine, anchovy, haddock, hake, salmon, tuna, turbot or monkfish among others. The number of larvae and their distribution in the fish depend on their marine habitats and on their dietary habits: larvae are housed mostly in the abdominal cavity and viscera in euphausid fish (balaladilla, herring, mackerel ). that in those that feed on other fish are usually in the musculature that surrounds the abdominal cavity of the fish. Some fish the national fishing grounds are highly parasitized, especially in specimens of hake , one of the most consumed specimens in our country. Other species such as the rooster or verdel suffer a minor parasite, thus representing a lower risk.
Anisakis larvae may also be present in cephalopod molluscs such as squid and octopus, but not in bivalves such as oysters, clams or mussels, or in crustaceans or river fish.
Which fish dishes are at risk of being parasitized by anisakids?
Cases of parasitization of people have been described on all continents, and in Western countries is practically the only fish contamination that must be taken into account. However, the most frequent human parasitization among humans is the opisthistorchiasis, although it only occurs in Southeast Asia.
In fact, human infestations from parasitized fish consumption are associated with eating habits that include consumption of raw fish or have not been sufficiently cooked. Habits of fish consumption can vary greatly depending on the culinary culture of each area, as well as their traditions.
For example, Japanese sushi and sashimi , salted or smoked herring , Nordic gravlax , Hawaiian lomi-lomi , South American cebiche, or anchovies in vinegar, typical of Spain, are considered risky dishes for the transmission of anisakids. others. However, these dishes will be safe if they are made with fish that has been previously frozen.
What kind of diseases can anisakis intoxication cause?
When eating food contaminated by Anisakis , two clinical conditions can occur, on the one hand the parasitization of the digestive tract, and on the other an allergic reaction whose symptoms can vary from an urticaria to anaphylactic shock. When both situations coincide, there is talk of gastroalergic anisaquiasis.
- Parasitation or infestation: is considered a zoonosis (human disease transmitted by animals) and is acquired by the consumption of fish or cephalopods raw or insufficiently cooked housing live larvae.
- Gastroallergic anisachiasis: defined as an acute allergic condition accompanied by digestive gastric symptoms, a consequence of the parasite symptoms and the antibody response generated by the parasite.
- Allergy to Anisakis : this is an acute allergic condition. It does not occur in the general population and does not require fish to be raw at the time of consumption. It is usually given in adult subjects who have never had allergies to other foods. The most common symptoms are cutaneous, although there are also cases of anaphylaxis.
- Other diseases: less frequent. Rhinoconjunctivitis and occupational asthma have been described in fishmongers and in fish handlers, as well as dermatitis among others.
What are the symptoms of the allergic reaction to these parasites?
The most common is an allergic picture that occurs between half an hour and two hours after eating fish. It occurs most often in adults between forty and seventy years of age. The detectable signs are as follows:
- On the skin: urticaria with generalized pruriginous hairs, and occasionally generates a swelling in the lips or eyelids.
- In the digestive system: pain in the abdomen, feeling full or full, nausea, vomiting and / or diarrhea.
- Generalized or anaphylaxis, with typical symptoms of urticaria, palmoplantar itching and genitalia. These symptoms are accompanied by respiratory and digestive symptoms, such as dizziness, loss of consciousness and feeling of death.
What symptoms does Anisakis parasite produce?
Once ingested by man, the larvae penetrate through the mucosa of the digestive tract. There are three clinical forms: gastric, intestinal, ectopic.
- Gastric form : symptoms appear less than twelve hours after eating contaminated fish. It coincides with the time when the larva enters the digestive tract. The affected person has severe pain in the upper abdomen, nausea and vomiting.
- Intestinal shape : symptoms appear between 48 and 72 hours after ingestion of contaminated fish. They usually consist of acute abdominal pain, vomiting, nausea and altered bowel rhythm causing constipation or diarrhea. Symptoms similar to acute appendicitis.
- Extragastrointestinal or ectopic : rarely, larvae manage to perforate the gastric or intestinal wall, reach the abdominal cavity and migrate to different locations: peritoneum, lung, pancreas, liver ... When this occurs, in the most severe cases surgery may be necessary. At times even less frequent, the larvae are able to trace from the stomach to the oropharynx, causing larvae to be expelled with cough.
For more information about Anisakis and its possible poisonings, consult with a specialist in Allergology .