This 61 year old restaurant owner was referred for upper endoscopy to evaluate typical longstanding dyspepsia and reflux type symptoms. His upper endoscopy appeared quite normal except for what initially appeared to be a wisp of mucin floating in the gastric fundus. On closer inspection, this worm like structure was seen and identified as the marine parasite anisakis simplex which is the cause of anisakiasis.
The life cycle of Anisakis starts when eggs produced by adult females are passed in the feces of infected marine mammals. They hatch and molt through several larval stages before being consumed by crustaceans, their first host. Following further maturation, the larva become infective to fish and squid when consumed. Once in marine hosts such as tuna or cod, the larva are infective when consumed by either marine mammals or humans. If the host dies, the larva migrate to the muscle tissues where through predation, they will pass onto another host. If instead they are consumed by marine mammals, they will mature in the host's intestine to shed eggs as adults. Humans become incidental hosts when they consume raw fish often in the form of sushi. The larvae hook into the gastric or intestinal wall and can cause a significant localized reaction and in some case peripheral eosinophilia. Most often, the clinical course following ingestion is asymptomatic: the larva briefly anchoring to the gastric or intestinal wall before dying and passing uneventfully. Larva have been reported to penetrate the mucosa and cause abdominal pain and vomiting. Small bowel lesions mimicking Crohn's disease have been noted. When seen endoscopically, removal as demonstrated in this case is curative. Generally, medical therapy is not necessary, but limited experience with albendazole has been reported.
Peter B. Kelsey, M.D., Harvard Medical School, Massachusetts General Hospital