What is Anisakis?
The genre Anisakis it includes some species of parasites that habitually populate the digestive system of certain fish, molluscs and marine mammals.
But that's not all: in addition to anisakiasis, these nematodes can be the protagonists of allergies. After eating raw food infected with Anisakis, some people's bodies produce type E immunoglobulins (IgE); an allergic reaction, even a serious one, follows (eg anaphylaxis).
- What is the life cycle of the Anisakis?
- What risk does the consumer of raw fish run?
- How can the risk of Anisakis infections be reduced?
Description and life cycle
DESCRIPTION
The Anisakis is a nematode belonging to the family of Anisakidae, composed of 5 genera, of which 4 cause diseases in humans and other animals:
- Anisakis, including Anisakis simplex And Anisakis physeteris
- Pseudoterranova
- Contracaecum
- Phocascaris
Among these just listed, the nematodes belonging to the genus Anisakis are probably the most frequent parasites transmitted by fish products to man.
The Anisakis has all the typical characteristics of nematodes: the body is cylindrical and vermiform, with a circular section, which differs well from that of flatworms (flat worms).
The Anisakis are large parasites, visible to the naked eye, often curled up on themselves: these nematodes, with a whitish or pinkish color, measure from 1 to 3 cm in length. These are pseudocoelomate parasites, therefore consisting of a false coelom, the cavity interposed between the alimentary canal and the body wall.
The parasite wall consists of three basic sections:
- Multi-layered cuticle, formed by collagen. To sneak into the host's stomach, the cuticle is indispensable for the parasite: this, in fact, acts as a shield against acid gastric juices.
- Middle epidermal layer
- Longitudinal muscle layer
The Anisakis are so-called "proctodeated" organisms, that is, they have a mouth for food intake and an anus for the emission of faeces.
BIOLOGICAL CYCLE
Like the vast majority of parasites, Anisakis have a complex life cycle. There are numerous intermediate guests, and man - in this specific case - is not the definitive guest as one might believe. The biological cycle takes place in the marine environment passing through various stages of development. To simplify, here is a list of the parasite's intermediate hosts:
- The Anisakis live in the stomach of marine mammals (whales, seals, dolphins); the unfertilized eggs of Anisakis are therefore released into the sea via the faeces → first stage
- Once in the water, the Anisakis eggs mature (are fertilized); subsequently, they come out of the egg and spread (larvae L2) → second stage
- The larvae are ingested by an intermediate host (e.g. planktonic crustacean): in this phase, the L2 larvae mature in L3 → third stage
- After eating the Anisakis, the crustacean is in turn ingested by a second intermediate host (fish, squid, etc.). When the host dies, the Anisakis larvae migrate to the liver, gonads, mesentery and, above all, in muscle tissues. Through predation, the larvae switch from fish to fish.
Herring, cod, mackerel, anchovies, monkfish and sardines are the most contaminated fish by Anisakis
At this point, the life cycle can complete or be interrupted:
- Marine mammals feed on fish, cuttlefish or squid with L3 larvae → the L3 larvae become adult worms, produce eggs and the cycle resumes
- Man, by eating raw or battered fish, embodies the guest accidental dell "Anisakis: arrived in the human intestine, the parasite, unable to complete its life cycle, dies.
Let us not forget, however, that Anisakis infections in humans can create gastrointestinal disturbances (abdominal pain, diarrhea, vomiting), up to stomach or intestinal perforations.
Anisakis infections
Anisakiasis are emerging zoonoses, due to the rapid spread of Anisakis nematodes: the intake of raw or undercooked fish contaminated with Anisakis larvae can trigger a gastrointestinal infection. The species most involved in anisakiasis is Anisakis simplex.
Symptoms
To learn more: Anisakiasis Symptoms
After a few hours from the ingestion of these contaminated fish, the victim complains of violent abdominal pain, nausea and vomiting. In some cases, the Anisakis larvae reach the intestine: in similar situations, after a couple of weeks from the "infection, the" The body may respond with a severe eosinophilic granulomatous response, causing symptoms that mimic Crohn's syndrome.
Fortunately, in the majority of diagnosed cases, the cure for the removal of the parasite is quite simple.
Complications
The Anisakis infection tends to resolve itself in a short time: the victim, eventually making use of therapeutic aids, heals completely in a matter of days.
Only rarely, Anisakis can cause severe obstructions in the small intestine: in this case, the patient will undergo surgery. Some patients may avoid surgery: therapy with albendazole may be sufficient.
Treatment
Information on the therapies available for the treatment of anisakiasis can be found in the article "Anisakis - Drugs and Treatment of" Anisakiasis ".
Prevention
The implementation of simple precautions allows you to consume the fish in total safety: the heat treatment (freezing / cooking), for a sufficiently long time, is essential to prevent anisakiasis.
The FDA always recommends freezing shellfish and fish intended for consumption at (at least) -35 ° C for 15 hours, or at -20 ° C for 7 days. Even cooking (the core of the product must reach 60 ° C for at least one minute) guarantees the removal and killing of the parasite from the fish.
Neither salting, nor marinating or smoking are effective preparative methods for killing Anisakis from fish.
Raw food fanatics, before consuming fresh fish that has not been thermally chilled, should be sure that it has been gutted immediately after fishing. Clearly, all fish intended for consumption should be carefully inspected "with the naked eye" for the detection of Anisakis parasites: we remember, in fact, that these nematodes reach considerable dimensions which make them visible to the naked eye.
Allergies from Anisakis
For some years now, Anisakis has been recognized as a possible vector of allergies.
Particularly sensitive individuals can develop allergies by simply handling infected fish. Anisakis allergies can also be contracted simply by inhaling airborne allergens during the processing of infected fish products.
In sensitive patients, not even adequate heat treatment guarantees immunity from these allergies. The larvae of parasites such as Anisakis and other related species (eg. Pseudoterranova spp., Hysterothylacium aduncum) can release biochemical substances (antigens) into the fish tissues, which are extremely resistant to freezing and cooking. The hypersensitive or allergic subject, in contact with these substances, develops allergic reactions of varying severity: the most frequent allergopathies are urticaria, angioedema and anaphylactic reactions, sometimes accompanied by gastrointestinal symptoms. Less frequent are asthmatic attacks, contact dermatitis and conjunctivitis after inhalation / consumption of fish contaminated with Anisakis larvae.
Antigenic protein exposure of Anisakis larvae → † ↑ IgE → IgE mediated reactions
The prick test and the search for specific antibodies against the larvae of these parasites are useful diagnostic investigations to ascertain the suspicion of allergy from Anisakis. Hypersensitivity to these parasites is assessed by the rapid increase in IgE levels in the days immediately following the consumption of fish contaminated by Anisakis.
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