The sealworm is a nematode (a worm) that parasites fish , mostly cod. There economical importance is large: cod need to be deep froozen before consumed. All the cod must be inspected before eaten.
The sealworm starts its live in the guts of the grey seal,`Halichoerus grypus, here seen together with the herrin gull.(1)
Live cycle seal worm
1The eggs become embryonated in water, and first-stage larvae (L1) are formed in the eggs. The larvae molt, becoming second-stage larvae(L2), and after the larvae hatch from the eggs, they become free-swimming(L3). According to new studies, anisakids already reach the third stage within the egg.
2 The eggs are part of the plankton, floating in the upperlevels of the sea. The eggs are eaten by small crustaceans. Inside theire body, the larvae develop into third-stage larvae (L3). Once the crustaceans are eaten by fish and squid they infect those fish and squid.
3 The larvae migrate from the intestine to the tissues in the peritoneal cavity and grow up to 3 cm in length. Upon the host’s death, larvae migrate to the muscle tissues, and through predation, the larvae are transferred from fish to fish.
4 Fish and squid maintain third-stage larvae that are infective to humans and marine mammals. When fish or squid containing third-stage larvae are ingested by marine mammals, like seals , the larvae molt twice and develop into adult worms. The adult females produce eggs that are shed by marine mammals.
5 Humans become infected by eating raw or undercooked infected marine fish. After ingestion, the anisakid larvae penetrate the gastric and intestinal mucosa, causing the symptoms of anisakiasis.
As far as it is known, the life cycle of species of Pseudoterranova also includes crustaceans as the first hosts, and fish as second hosts.
Just along the South America coasts, sealworm larvae have been reported in at least 40 species of marine fish belonging to 21 families and 10 orders see (Additional file 1: Table S1). In this region, sealworm larvae infect the flesh of economically important fishes e.g. [13, 14, 15] and cause zoonotic diseases when humans consume raw or undercooked fish
Pseudoterranova decipiens reside in the stomach of marine mammals, where they are embedded in the mucosa, in clusters. Unembryonated eggs produced by adult females are passed in the feces of marine mammals . The eggs become embryonated in water, and first-stage larvae are formed in the eggs. The larvae molt, becoming second-stage larvae , and after the larvae hatch from the eggs, they become free-swimming . Larvae released from the eggs are ingested by crustaceans . The ingested larvae develop into third-stage larvae that are infective to fish and squid. The larvae migrate from the intestine to the tissues in the peritoneal cavity and grow up to 3 cm in length. Upon the host’s death, larvae migrate to the muscle tissues, and through predation, the larvae are transferred from fish to fish . Fish and squid maintain third-stage larvae that are infective to humans and marine mammals .
When fish or squid containing third-stage larvae are ingested by marine mammals, the larvae molt twice and develop into adult worms. The adult females produce eggs that are shed by marine mammals . After ingestion, the anisakid larvae penetrate the gastric and intestinal mucosa, causing the symptoms of anisakiasis.
– According to Bonner, cod worms (and other similar species) are “universal in the pinnipeds” (seals) and apparently do not cause the animals any significant harm. Bonner reports seeing “grey seals in excellent condition and with ample blubber reserves whose stomachs contained more than two litres of large nematodes.” (Bonner, 1990, p 133)
– In the cod, the larvae encyst in the muscles, where they remain dormant until the fish is eaten by the final host, the seal. This does not appear to place any great stress on the cod. In the warm stomach of the seal the larvae emerge from the cysts, finally mature and produce eggs.
– “The mature worms produce huge quantities of eggs which are shed into the water in the feces of the seal and hatch within 10-60 days, depending on water temperature.” (Bonner, 1990)
Consumption of sea fish, undercooked or raw can be a cause of anisakidosis following the ingestion of nematode larvae of sealworm and other members of the family Anisakidae. The most infected fish are herring, pollock, saithe and cod. In a recent Danish study 90% of wild fish catched was infected with nematodes.(4)
sympoms of anisakidosis
acute form: abdominal pain, vomiting with small amounts of blood. This is due to the entering of the worm through the wall of the stomach: Also : skinrash.
Therapeutic and diagnostic procedure: The larvae can then be eradicated during endoscopy, this is both the diagnostic and therapeutic procedure.
If anisacid penetrates the stomach, the patient may complain of the following symptoms:Abdominal pain.They are of an incomprehensible nature: it is difficult to determine exactly where it hurts, what character such feelings are.Pain is not always acute, which is why an ordinary person reacts to a change in state not immediately.Frequent vomiting.Sometimes they end in severe vomiting.
In the acute form, appears gastric pain within hours following the contaminant meal. These pain, due to the penetration of the mucosa by one or several larvae, can be accompanied by some allergic manifestations. The larvae can then be eradicated during endoscopy, diagnostic and therapeutic procedure. Late intestinal form, is most often discovered incidentally, post-operative ; by setting histological evidence of larvae in a granuloma responsible of a tumor syndrome (pain, obstruction, bleeding).
The chronic form occurs in sensitized patients, regular consumers of infected fish, even cooked. It is due to a thermostable A simplex allergen which may lead to chronic urticaria, angiœdema or also anaphylactic shock. Many immune mechanisms involving the expression of cytokines induced by the presence of the parasite (Ig production E) associated with genetic predispositions are also involved. These chronic forms are frequently reported in Spain, where consumers of fish are numerous.
Biological tests are sometimes difficult to interpret because of the antigenic relationship between two nematodes of the same family (Ascaridoidea) : A. simplex and Toxocara canis. The best diagnostic and therapeutic element of this new form of anisakidosis is to stop eating parasitized fish allowing the disappearance of clinical manifestations, especially hives.
Description, microhabitat selection and infection patterns of sealworm larvae (Pseudoterranova decipiens species complex, nematoda: ascaridoidea) in fishes from Patagonia, Argentina Jesús S Hernández-Orts et all
4 Nematode infections of maricultured and wild fishes in Danish waters: A comparative study Article