An Overview of Anisakis Infection

Also referred to as Anisakiasis, Anisakis Infection occurs from the accidental consumption of roundworm larvae, specifically the types of nematodes known as Pseudoterranova decipiens and Anisakis simplex.

When adult forms of Anisakis simplex and Pseudoterranova decipiens inhabit the stomach of sea mammals, the roundworms bury themselves in clusters into the mucosa of the stomach and produce unembryonated eggs which pass through the mammal’s feces.

In water, the eggs become embryonated, forming new larvae within the confine of the egg. The first-stage larvae then enter the molting stage, after which the larvae hatch from the egg and become freely swimming entities. The larvae are then consumed by crustaceans as they swim and within the crustacean hosts, the larvae develop further so that they are ineffective to the likes of squid and fish.

Within the crustacean host, the larvae travel through the intestines to the peritoneal cavity where they can grow up to three centimeters long. When the crustacean host dies, the larvae travel to muscle tissues and are consumed by fish to fish, traveling to new hosts through this means. At this stage, the squid and fish act as hosts for the larvae which are ineffective to mammals.

When the squid and fish hosting the third-stage larvae are consumed by marine mammals or humans, the larvae enter the molting stage twice consecutively and become fully adult worms. Then, the life cycle is repeated by adult female roundworms which produce eggs within the marine mammal hosts.

Humans incur Anisakiasis from the consumption of infected marine fish served undercooked or entirely raw. When the larvae enter the intestinal and gastric mucosa of the human host, symptoms of Anisakiasis will manifest.

Anisakiasis occurs worldwide and is more common in places where raw fish is consumed more readily. Symptoms of Anisakiasis include severe abdominal pain, vomiting, and nausea. Such symptoms may start only hours after the infected larvae are ingested by an individual. More often than not, the larvae are expelled from the body by coughing, however, should the larvae travel to the bowel, the individual may suffer from escalated eosinophilic granulomatous approximately one to two weeks after the initial infection. Symptoms in such instances may be similar to those of Crohn’s disease.

Diagnosis of Anisakiasis requires a gastroscopic examination. A medical professional may remove any larvae over 2 cm. A biopsy or a tissue sample taken during surgery could be used to test for Anisakiasis using a histopathologic examination. The treatment for Anisakiasis will require endoscopic or surgical removal done by your healthcare provider.