Scientific name. Anisakis simplex, A. physeteris, Pseudoterranova decipiens
Geographic distribution. Occurs wherever raw fishes are consumed. Japan, Netherlands, Germany, France, Korea, Hawaii, Alaska and West Coast states of USA.
Life cycle. The principle hosts of Anisakis are dolphins, porpoises, and whales; those of Pseudoterranova are seals, fur seals, walrus and sea lions. Eggs (40×50 ㎛) are discharged with the feces, and hatch in the cold water. L2 larvae are eaten by krill and develop into L3 larva. L3 larvae are transferred by the predatory food chain. The life cycle is completed when the infected fishes or squids are eaten by marine mammals, Humans are accidental or unsuitable host, so no maturation takes place. Herring, salmon, common mackerel, cod, conger eel and squid can transmit Anisakis, whereas cod, halibut, flatfish, and red snapper can transmit Pseudoterranova infection.
Morphology. The larvae of the family Anisakidae are characterized by the presence of three bilobed lips, a boring tooth near the dorsal lip, large excretory gland cells in their anterior region, and a ventriculus between the esophagus and the intestine. Distinction among the three genera depends on the presence or absence of an intestinal cecum and a ventricular appendix.
Pathology and Clinical Symptoms. The gastric or intestinal wall is thickened as a result of edema and inflammation. Ulcers or hemorrhages are occasionally seen. The mechanism of pathologic changes may be associated with allergic reactions to the secretory-excretory products of the larvae. Main symptoms are epigastric pain, nausea and vomiting which develop 6 hours after the ingestion of raw seafoods. P. decipiens larvae often provoke a tingling throat syndrome, associated with larval migration from the stomach to the mouth.
Diagnosis. Patients with gastric pains with history of eating raw seafoods, gastroscopy should be considered.
Treatment. In acute infection, larvae should be removed by gastroscopy. No effective chemotherapy is available.
Prevention. Avoid eating raw fishes in the endemic areas. Freezing of raw fish under -20℃ for 60 hours kills the larvae.
Kyoung Hwan Joo
Third-stage Anisakis larva, lateral view of tail. Showing the characteristic mucron on posterior end.
Anisakis Type I larva showing ventriculus. x200
Chong Yoon Joo
Posterior part of Anisakis Type I larva showing short tail with mucron. x200
Chong Yoon Joo
Anterior portion of the 3rd stage larva of Anisakis simplex.
Ventricular portion of the 3rd stage larva of A. simplex.
Tail portion (with a mucron) of the 3rd stage larva of A. simplex.
SEM view of anterior portion of the 3rd stage larva of A. simplex.
SEM view of middle portion of the 3rd stage larva of A. simplex.
SEM view of tail portion of the 3rd stage larva of A. simplex.
Anterior portion of the 4th stage larva of A. simplex.
Ventricular portion of the 4th stage larva of A. simplex.
Tail portion of the 4th stage larva of A. simplex.
SEM view of middle portion of the 4th stage larva of A. simplex.
SEM view of tail portion of the 4th stage larva of A. simplex.
Gastrofiberscopic findings in gastric anisakiasis.
Haemorrhage and edematous mucosa with erosion are observed.
Experimental anisakiasis in rabbit stomach. Y-shaped lateral cords are distinct on the transverse sections of the larvae.
Tai Soon Yong
A cross section of anisakid larva shows thich polymyarian muscle layer, ventriculus, Rennette cell, and bi-columned lateral cords. Note an cellular infiltration around the larva. H & E stain.
Cross sectional view of the esophagus-level of A. simplex larva, H&E stained.
Cross sectional view of the anterior intestinal-level of A. simplex larva, H&E stained.
Cross sectional view of the middle intestinal-level of A. simplex larva, H&E stained.
Endoscopic view of gastric anisakiasis.