Everything you need to know about Anisakis

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What is Anisakis?

Anisakis is a parasite that can be found in marine fish and cephalopods (squid, octopus, cuttlefish...). Its adult larva can be detected with the naked eye. Eating fish with Anisakis often causes digestive disorders such as gastroenteritis, stomach pain, vomiting, nausea, constipation, diarrhea ... and an allergic reaction that can range from hives to anaphylaxis (severe allergic reaction).

The biological cycle of Anisakis simplex is roughly as follows: fertilised eggs are expelled into the sea through the faeces of definite hosts (large marine mammals). These eggs house the larva in its initial state (L1) from where it will evolve to the L3 state. In order to reach L3, the larva needs to infect other fish, to lodge in them, and it does so by first passing through the plankton crustaceans. The fish, cephalopods and whales will eat the plankton and become infected.They can also be infected if they ingest fish that are already contaminated with Anisakis larvae. The parasite will have already reached level 3 and this is when we humans come into action, this is when we can get infected if we eat contaminated raw or undercooked fish dishes.

What are the symptoms of Anisakis?

Hombre con dolor de estómago

Once a person has ingested Anisakis larvae, they enter the body through the mucous membrane of the digestive tract. Three clinical forms are distinguished: gastric, intestinal, ectopic.

- Gastric form. It occurs when the larva enters the digestive tract. The symptoms of its presence will appear in less than twelve hours and consist of intense pain in the upper abdomen, nausea and vomiting.

- Intestinal form. In this case, symptoms will appear between 48 and 72 hours after eating contaminated fish. Acute abdominal pain, vomiting, nausea and alteration of the intestinal rhythm usually occur, causing constipation or diarrhoea. Symptoms may resemble acute appendicitis.

- Extragastrointestinal or ectopic. It occurs on rare occasions and what happens is that the larvae perforate the gastric or intestinal wall, reach the abdominal cavity and migrate to different areas: peritoneum, lung, pancreas, liver ... "When this occurs, in the most severe cases may require surgery. On even less frequent occasions, the larvae are capable of going up from the stomach to the oropharynx, producing the expulsion of the larva with the cough", tells us María Teresa Audicana, allergist of the IMQ Amárica Medical Center in Vitoria-Gasteiz, expert in food and child allergies and member of TopDoctors.

According to Audicana, what occurs most often after ingestion of Anisakis is an allergic reaction within half an hour or two hours of eating the infested fish. The symptoms are: hives on the skin (habones), swelling of the lips or eyelids, abdominal pain, sensation of satiety or fullness, nausea, vomiting and/or diarrhea, palmoplantar itching and in genitals and in more serious cases dizziness, loss of consciousness and feeling of death.

Is Anisakidosis the same as having an allergy to Anisakis?

No. Anisakidosis refers to human parasitism of the genus Anisakis, Pseudoterranova or Contracaecum. If we speak of Anisakiosis we are referring to the infection by the genus Anisakis, although the term Anisakidosis is also used for the same. Allergy to Anisakis, is  an allergy to the parasite (its protein).

Can Anisakis be removed from the body?

The good news is that we humans are not the best hosts for Anisakis and the L3 larva does not usually thrive into the adult stage within our organism. The parasite is either eliminated by faeces or vomiting or dies in cysts in about 15 days.

"The most effective treatment for gastric Anisakiosis is the extraction of larvae during endoscopy, which leads to diagnostic confirmation and the consequent disappearance of the symptomatology within a few hours. In intestinal Anisakiosis, on many occasions, it is necessary to perform surgery and resection of the affected fragment. However, when the suspicion of intestinal Anisakiosis is firm, conservative treatment with serotherapy and antibiotics may be sufficient for healing. In colon Anisakiosis, larva extraction by colonoscopy can be successfully performed. Although numerous antiparasitic (anthelmintic) treatments such as pyrantel pamoate, thiabendazole and ivermectin, among others, have been investigated, there is currently no effective pharmacological treatment. The larvae of A. simplex (anisakis genus responsible for human infection) have been shown to be highly resistant to this type of drug while those of P. decipiens (Aisakis genus that also parasitizes humans but to a lesser extent, known as cod worm) seem to be sensitive to ivermectin, at least in in vitro studies," says the allergist Maria Teresa Audicana.

What fish can have Anisakis?

Merluza cocida con anisakis

Any marine fish can be infected with Anisakis larvae. If we look at the species that we usually consume the most, the most affected are: herring, sardine, anchovy, haddock, hake, salmon, tuna, turbot or monkfish, among others. Anisakis larvae can also infect cephalopods such as octopus and squid. 


What fish do not have Anisakis?

Audicana states that fish that are free of Anisakis are bivalves (oysters, clams, cockles, mussels ...), crustaceans (shellfish) and river fish (trout, carp, perch). 


Is the Anisakis visible to the naked eye?

The Anisakis is a pearly white worm about two centimetres long that can be found in the viscera of infected fish. It can also be seen as a spiral in the skirt of the fish.

How to avoid Anisakis?

To avoid getting Anisakiasis, do not eat raw or cooked infected fish that has not killed the parasite. These are the recommendations from AECOSAN (Spanish Agency for Consumption, Food Safety and Nutrition) to avoid infection:

Buy the fish clean and without viscera (intestines). If it has not been cleaned in the fish shop, it should be done at home as soon as possible, removing the viscera and washing the surrounding area well to prevent the larvae from passing from the viscera to the fish meat and the fish.

- Cook, fry, bake or grill at 60ºC for at least one minute and the whole piece. 

-Although the consulted allergist affirms that crustaceans do not have Anisakis, AECOSAN recommends following the previous recommendation with lobster, prawns, lobster, shrimp, shrimp, crab, spider crab...

- If the fish is to be eaten raw or in preparations that do not kill the parasite, it must be frozen beforehand. If you are going to freeze at home, make sure that the fridge reaches a minimum of -20ºC (three star refrigerators or more) and keep the fish frozen for five days. In case our refrigerator is not three stars, it is recommended to buy the already frozen fish.

What should be frozen?

Boquerones en vinagre

Following AECOSAN's recommendations, we will have to freeze these preparations if we make them at home. If we buy them prepared it will not be necessary because the freezing will have been done by the manufacturer.

- Anchovies in vinegar and pickled fish.

- Sashimi, sushi, carpaccios and other specialties based on raw fish.

- Marinated fish, such as ceviche or salmon.

- Raw or practically raw fish eggs.

- Herring and other raw fish prepared in brine or lightly salted.

- Marine fish subjected to cold smoking.


What you don't need to freeze

- Oysters, mussels, clams, coquinas and other bivalve molluscs.

- Fish from inland waters (rivers, lakes, marshes, etc.) and freshwater fish farms. For example: trout, carp... If the fish comes from a saltwater fish farm,  there is a minimal risk of anisakis 

- Semi-preserves such as anchovies (in metal containers, glass or other presentations).

- Dried fish salted in the traditional way, such as cod or mojamas that we buy already prepared.

Is there more Anisakis now than before?

"The presence of anisakids is increasing in the last ten years in fishery products, due to marine pollution and fishing practices. It could be stopped, improving evisceration practices in fishing vessels (which do not throw the viscera to the sea because if they are contaminated will return to the food chain of fish), improving the labeling of fishery products indicating the recommendations to follow (warming 60 º C, freezing -20 º C more than 24h) and developing a vaccine against allergy to anisakids, "says Monica Carrera, biologist and researcher at the Institute of Marine Research IIM-CSIC Vigo.

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