ANISAKIS: “A bitter enemy for those who consume raw fish”

ANISAKIS: A bitter enemy for those who consume raw fish

Anisakis is a genus of nematodes (worms), parasites of many fishery products, as well as potential pathogenic parasites for humans.

They usually inhabit in the digestive tract of some families of fish, mollusks and marine mammals living in Mediterranean sea and Atlantic, Pacific and Indian Oceans as: dolphins, seals, salmons, cods, anchovies, sardines, herrings, mackerels, anglerfishes, Saint Peter’s fishes, scabbard fishes (very often infested), shortfin and common squids.

Anisakis larvae in fish products are visible by naked eye, they ranging from 15 to 30 mm long and are located on serosal surface of liver, ovary, stomach and intestine, where they encysts  and takes on characteristic coiled form, look like whitish or pinkish little worms.

Figure 1. Anisakidae larvae. (from Wikipedia httpen.wikipedia.orgwikiFileAnisakids.jpg).

Originally from en.wikipedia; description page is/was en:Image:Anisakids.jpg.

 

 THE LIFE CYCLE OF ANISAKIS 

1. Adult worms are found in the stomach of marine mammals and other seafoods, and their unembryonated eggs are passed in the feces → FIRST STEP

2. Eggs become embryonated in seawater and larvae hatch from eggs → SECOND STEP

3. Larvae are ingested by crustaceans → THIRD STEP

4. Infected shellfish get eaten by fish and squid, where the larvae make their way into the liver, gonads, mesentery, and especially into the muscle tissues. 

5. The life cycle is completed with the ingestion of infected fish or squid by other marine mammals, birds and reptiles. Larvae develop into adult worms and produce eggs that are shed by marine mammals so the life cycle start again.

6. Humans are usually infected by the accidental consumption of raw or undercooked marine fish that harbor the infected larvae. In the human gut, the parasite is not able to conclude its life cycle and DIES.

(Anisakis cannot be transmitted from human to human)

 

EPIDEMIOLOGY

This parasite worm can cause disease in humans called “anisakiasis”, it is frequently widespread in areas of the world where fish is consumed raw, as Scandinavian countries and Japan, although with globalization of foods it is slowly spreading almost everywhere.

Humans can also be accidental hosts for these nematode parasites, caused by the consumption of raw or undercooked infested seefood.

The risk is given by late, inadequate or not gutted freshly caught fish, this cause relocating Anisakis larvae from muscle tissue (fish flesh) into the gut and now is not possible noticed the contamination. 

 “The World Health Organization (WHO) recommends that freshly caught fish should be gutted, cooked and frozen (-23 ° C for at least a week) as soon as possible”

For the worm, humans are a dead-end host. Anisakis larvae cannot develop in humans but can be alive in their digestive tract for a while; sometimes, within a few hours of ingestion, the parasitic worm gets stuck and dies without symptoms; but in some cases, especially if are eaten many larvae, you may have invasion of gastric or intestinal mucosal with consequences as:

  • abdominal pain, nausea, vomiting, fever
  • inflammatory reaction with a severe eosinophilic granulomatous response
  • ulceration of the intestinal mucosa, with perforation of the intestinal wall
  • acute allergic manifestations, such as anaphylaxis, urticaria and angioedema

 

DIAGNOSIS &TREATMENT

Diagnosis is based on historical data (ingestion of raw seafood) and the kind of symptoms. In some cases, the infection will resolve with the only symptomatic treatment. In other cases, however, infection can lead to small bowel obstruction, which may require surgery.

 

PREVENTION

Anisakis is able to survive to many treatments as cold smoking, marinating, salting and refrigerated temperatures. It can be killed only by adequate cooking at temperatures greater than 60°C (at least 10 minutes) or freezing (-20°C for at least 24 hours). For this reason consuming raw fish products without the right treatments can be considered a risk behavior.

It is thought that eating wild fish it is more at risk than farmed fish.

 To prevent anisakiasis we recommend:

  • avoid raw or undercooked fish or shellfish raw or undercooked
  • buy gutted seafoods, because the complete evisceration allows the expulsion of the parasite by the muscles of the fish
  • limit consumption of risk products such as homemade preserves of marinated bluefish
  • risky seafoods should be properly cooked (almost 63°C)
  • freeze at -20°C for 7 days

“From the institutional point of view, in Europe there are specific rules about it (EC Regulation no. 178/2002 of 28 January 2002), which establish surveillance networks on food security, with notifiable”

Be careful and eat with knowledge!

 

 

 

 

 


  •  Foodborne disease outbreaks: Guidelines for investigation and control, Ginevra, WHO Press, 2008, ISBN 978-92-4-154722-2.
  • Harrison, Principi di medicina interna, Milano, McGraw-Hill, 2005, p. 1423.
  • Casabona et al.,Global Food Security: Ethical and Legal Challenges, Wageningen Academic Pub, 2010, pp. 240-241.

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