Anisakis Simplex

What can I say about Anisakis as a layperson, not a lot. I have been eating sushi in Japan for 30+ years and I have never had any type of problem, at least that I know of. But Anisakis is not something I would like to experience and I am very careful about what I eat, where and when. Just too many restaurants serve fish in raw form and contaminate clients by transfer of bacteria. Hygiene is critical but not always enough.

Anisakiasis the disease caused in humans by Anisakis simplex. It is frequently diagnosed when the affected individual feels a tingling or tickling sensation in the throat and coughs up or pulls out a roundworm. Symptoms occur from as little as an hour to about 2 weeks after consumption of raw or undercooked seafood. With their front ends, these larval roundworms from fish or shellfish usually burrow into the wall of the intestine and occasionally they penetrate the intestinal wall completely and are found in the body cavity.

The worm has hooks on it’s mouth-parts and in the host’s intestine it can detach itself and move about, reattaching itself to other sites, Anisakis simplex rarely reaches full maturity in humans and is usually eliminated spontaneously from the intestine within 3 weeks of infection.

Worms that die in the tissues are eventually removed by the host’s scavenger cells but can cause inflammation that can mimic appendicitis or more serious conditions. This is fortunately rare with only 8 cases appearing in the literature from Spain, the source of my information on this subject. However at least 2000 cases (mostly minor) occur in Japan amounting to 95% of the annual world total.

Anisakis simplex is a roundworm that as an adult is a parasite of sea mammals. It has a complicated life cycle. The adults of Anisakis simplex are found in the stomachs of whales and dolphins. The fertilized eggs from the female parasite pass out of the host with the host’s faeces. These then develop into larvae that hatch in the seawater.

The larvae are eaten by copepods (small shrimp-like creatures) and other small invertebrates. The larvae grow inside the host animal and when they have developed to the next stage pass out and infect the next host, a fish or a squid. The larvae may burrow out through the bowel wall into the muscles of the second host. These parasites are known to occur frequently (well over 40% and in some studies up to 100% of the fishes studied) in the flesh of cod, haddock, fluke, Pacific Salmon, Herring, Flounder and Monkfish.

Some evidence exists that the roundworm larvae move from the bowel to the flesh if the fish hosts are not gutted promptly after catching. I am also told that fishing boats are throwing infected fish guts over board and hosts are infected as they feed on the contaminated fish.