Anisakis simplex also known as the herring worm, Pseudoterranova decipiens also known as cod or seal worm from the families of Phocanema and Terranova, Contracaecum species and Hysterothylacium or Thynnascaris species are anisakid nematodes or roundworms, which have been incriminated in human contaminations triggered by the ingestion of raw or improperly cooked seafood with the help of medical microscopy using a microscope. Up to now, merely Anisakis simplex and Pseudoterranova decipiens are documented from human cases in North America.
Anisakiasis is commonly called when referring to the acute illness in humans. Certain purists use generic terms such as contracaeciasis in referring to the illness, but the most believe that the name derived from the family is sufficient. The range of clinical characteristics is not reliant on species of anisakid parasite in instances documented to date.

In North America, anisakiasis is most often diagnosed once the inflicted person experiences a stinging or prickling feeling in the throat and coughs up or manually removes a nematode. In more serious instances there is acute abdominal pain, more like acute appendicitis complemented by a nauseous sensation. Manifestations transpire from as little as an hour to approximately two weeks after ingesting of raw or inadequate seafood. One nematode is the common number taken from a patient. With their anterior ends, these larval nematodes from fish or shellfish commonly burrow into the wall of the digestive tract to the point of the muscularis mucosae as monitored through medical microscopy using a microscope. Sporadically they infiltrate the intestinal wall fully and are discovered in the body cavity with the help of medical microscopy using a microscope. They generate a substance that invites eosinophils and other host leukocytes to the area. The penetrating host cells develop a granuloma in the tissues around the infiltrated worm as observed by means of medical microscopy using a microscope. In the digestive tract lumen, the worm can unfasten and attach again to other locations on the wall. Anisakis rarely attain complete maturity in humans and commonly are eradicated spontaneously from the digestive tract lumen within three weeks of contamination. Infiltrated worms that die in the tissues are finally taken away by the phagocytic cells of the host.

In instances where the patient regurgitates or coughs up the worm, the illness may be diagnosed by morphological test of the nematode. Ascaris lumbricoides, the big roundworm of humans, is a terrestrial relative of anisakines and at times these larvae also creep up into the throat and nasal passageways. Other instances may need a fiber optic tool that permits the attending physician to examine the interior portion of the stomach and the first section of the small intestine. Such examination is done through the help of medical microscopy using a microscope. These tools are equipped with a mechanical forceps that can be utilized to take away the worm. Other instances are diagnosed upon discovery of a granulomatous lesion with a worm on laparotomy. A particular radioallergosorbent examination has been created for anisakiasis but is not yet commercially advertised.

Sea foods are the main sources of human contaminations with these larval worms. The mature types of Anisakis simplex are discovered in the stomachs of whales and dolphins with the aid of medical microscopy. Fertilized eggs from the female parasite get out of the host via the stools of the host. In seawater, the eggs embryonate, growing into larvae that hatch in sea water. These larvae are infective to copepods, which are small crustaceans associated to shrimp, and other small invertebrates. The larvae develop in the invertebrate and turn infective for the next host, a fish or larger invertebrate host like a squid. The larvae can infiltrate through the digestive tract into the muscle of the second host as observed through medical microscopy. Certain proof exists that the nematode larvae transfer from the viscera to the flesh if the fish hosts are not gutted quickly after catching. The life cycles of all the other anisakis genera incriminated in human contaminations are alike. These parasites are recognized to transpire oftentimes in the flesh of cod, fluke, pacific salmon, herring, flounder and monkfish.

Nevertheless, it is alleged that many other instances go unnoticed. The illness is transferred by raw, improperly cooked or inadequately frozen fish and shellfish, and its prevalence is anticipated to escalate with the rising popularity of sushi and sashimi bars.
Serious cases of anisakiasis are incredibly painful and need surgical intervention with the aid of medical microscopy using a microscope. Physical elimination of the nematode from the lesion is the only recognized procedure of lowering the pain and eradicating the cause other than waiting for the worms to expire. The signs visibly persist after the worm expires since certain lesions are discovered upon surgical removal that has only nematode remnants. Stenosis, which is a narrowing and stiffening of the pyloric sphincter was noted in an instance wherein exploratory laparotomy had exposed a worm that was not taken away.