Anisakis, a common parasite in fish

When talking about food safety we almost always begin with bacteria, viruses and chemical toxins. But there is a group of problems which should not be neglected, such as those produced by parasites.

People tend to think that they are not really dangerous because many parasites can be seen with the naked eye. If consumers are repelled they end up not eating contaminated food. This is partly true, but the case of Anisakis simplex and other members of its family should be considered with care.

The larvae of this parasite are ingested when eating raw or undercooked fish. Anisakis are worms with bodies that lack segmentation, like earthworms. They are small, usually about 3 cm long and less than 1 mm in diameter, and whitish, almost transparent, in colour. Because of these characteristics they are often almost undetectable and are easily consumed without being seen.

Disease-producing forms of Anisakis are found in fish, and humans enter their life cycle by accident. For the parasite to reach fish it needs marine mammals, which is why it appears less frequently in Mediterranean fish than in fish from other, colder, seas.

Anisakis is a very aggressive parasite. Its teeth cut through tissue and pierce it. This provokes acute pain in the infected person, depending on what part of the body, usually between the mouth and the small bowel, the parasite fastens to.
Anisakis parasites are frequently found in various species of commercial marine fish, such as blue whiting, mackerel, hake, cod, sardines or anchovies. Larvae are found in the liver, abdominal cavity, muscles and in all the entrails. Sometimes hundreds of larvae can appear in one single fish.

Humans eat live larvae when they eat raw or undercooked fish. The larvae provoke ulcers and inflammation of the gastrointestinal track. Symptoms will be more or less serious depending on the amount of larvae ingested.

Although a few years ago treating an Anisakis infection always required surgery, nowadays there are drug combinations that can control and eliminate the parasite. This is why it is considered an intermediate to minor problem.

But, is it possible to eradicate or control this parasite? Yes. Fish should be well cooked or frozen at temperatures under –20ºC (-4ºF) for 24 hours. This is why raw fish poses the most serious hazard. In Spain, anchovies in vinegar is one of the most dangerous dishes. As a preventive measure, you should consider freezing it before eating it.

However, once the parasite is destroyed, an allergic reaction to its remains may appear, although the number of cases does not seem to be important.
 

Did you know...

The main characteristic of horse meat is its tenderness. It tastes similar to veal, and contains high levels of myoglobin and iron.

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