''Anisakis simplex'', known as the herring worm, is a species of nematode in the genus ''

Anisakis ''Anisakis'' (a·nuh·saa·keez) is a genus of parasitic nematodes that have life cycles involving fish and marine mammals. They are infective to humans and cause anisakiasis. People who produce immunoglobulin E in response to this parasit ...

''. Like other nematodes, it infects and settles in the organs of marine animals, such as

salmon Salmon () is the common name In biology, a common name of a taxon or organism (also known as a vernacular name, English name, colloquial name, country name, popular name, or farmer's name) is a name that is based on the normal language of ...

, mackerels and

squids True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fitting ...

. It is commonly found in cold marine waters, such as the

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the contine ...

and

Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth#Surface, Earth's surface and about 29% of its water surface area. It is known to separate the "Old World" of Afr ...

. This species begins as an egg found in the

faeces Feces ( or faeces), known colloquially and in slang as poo and poop, are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the large intestine. Feces contain a relati ...

of its host, and hatches as a second-stage

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. Th ...

in the ocean, where it survives for several days. This larva is then consumed by an intermediate

host A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places *Host, Pennsylvania, a village in Berks County People * Jim Host (born 1937), American businessman * Michel Host ...

, usually a

krill Krill are small crustaceans of the order Euphausiacea, and are found in all the world's oceans. The name "krill" comes from the Norwegian word ', meaning "small fry of fish", which is also often attributed to species of fish. Krill are consid ...

, and it develops into a third stage larva within the body of this intermediate host. The krill is then ingested by a

predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill ...

, such as squid or fish, which act as the paratenic host for ''A. simplex''. The worm reaches the end of its life cycle when the paratenic host is ingested by a

whale Whales are a widely distributed and diverse group of fully aquatic placental marine mammals. As an informal and colloquial grouping, they correspond to large members of the infraorder Cetacea, i.e. all cetaceans apart from dolphins and ...

or another marine mammal. In the abdominal cavity of this final host, ''A. simplex'' develops into a fully mature worm and reproduces to form eggs, which are then expelled from the body of the final host. ''A. simplex'' generally possesses digestive and excretory organs, such as an

oesophagus The esophagus (American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an Organ (anatomy), organ in vertebrates through which food passes, aided by Peristalsis, peristaltic contracti ...

and

intestine The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans a ...

. However, its morphological structure changes as it develops from one life stage to another. When it is fully mature, it has defined lip structures, a regularly patterned outer surface, and fully developed reproductive organs. The consumption of raw or undercooked seafood, such as

sashimi is a Japanese delicacy consisting of fresh raw fish or meat sliced into thin pieces and often eaten with soy sauce. Origin The word ''sashimi'' means "pierced body", i.e. " 刺身" = ''sashimi'', where 刺し = ''sashi'' (pierced, stu ...

and

ceviche Ceviche () is a Peruvian dish typically made from fresh raw fish cured in fresh citrus juices, most commonly lime or lemon. It is also spiced with '' ají'', chili peppers or other seasonings, and julienned red onions, salt, and cilantro are ...

, puts humans at risk for developing an

infection An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable d ...

allergic reaction Allergies, also known as allergic diseases, refer a number of conditions caused by the hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include hay fever, food allergies, atopic derm ...

caused by ''A. simplex''. The worm can infect the stomach or intestine by lodging itself within the walls of the organ and producing digestive enzymes to penetrate mucus layers. It occasionally pierces through the wall completely and travels in the abdominal cavity. Acute symptoms, such as abdominal cramps,

nausea Nausea is a diffuse sensation of unease and discomfort, sometimes perceived as an urge to vomit. While not painful, it can be a debilitating symptom if prolonged and has been described as placing discomfort on the chest, abdomen, or back of the ...

and

diarrhoea Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration often begin wi ...

, arise hours after ingestion.Pravettoni, V., Primavesi, L., & Piantanida, M. (2012)
Anisakis simplex: current knowledge
''European Annals of Allergy and Clinical Immunology, 44''(4), 150-156. The infection can be chronic if not treated. Treatment involves removal of the worm by

endoscopy An endoscopy is a procedure used in medicine to look inside the body. The endoscopy procedure uses an endoscope to examine the interior of a hollow organ or cavity of the body. Unlike many other medical imaging techniques, endoscopes are inse ...

or surgery.

Taxonomy

The ''Anisakis simplex'' is a

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson ha ...

roundworm classified under the

phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclatu ...

Nematoda The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-parasitic nematodes also known as eelworms. They are a diverse animal phylum inhabiting a broa ...

.Gang, S., & Hallem, E. (2016). Mechanisms of host seeking by parasitic nematodes. ''Molecular and Biochemical Parasitology, 208''(1), 23–32. Ritter, J. (2001).
Anisakis simplex
'. Retrieved April 17, 2021. It possesses the typical characteristics of its phylum, including an unsegmented, cylindrical body that occasionally fills up with fluids and allows it to swim freely. Like other nematodes, ''Anisakis simplex'' communicates through its sense organs that detect chemicals and motion. These nematodes have the tendency to infect and inhabit the organs of other animals, who act as their host. ''A. simplex'' is also part of the Anisakidae

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

and the ''Anisakis''

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

, which are specifically known for their potential to spread diseases from one species to another, starting with the infection of animals, such as fish, and eventually leading to transmission in humans.

Morphology

''Anisakis simplex'', like typical worms from the Anisakidae has an oral pore, oesophagus, ventriculus, intestine and anal pore to aid with ingestion and

excretion Excretion is a process in which metabolic waste is eliminated from an organism. In vertebrates this is primarily carried out by the lungs, kidneys, and skin. This is in contrast with secretion, where the substance may have specific tasks afte ...

. The morphological features of ''A. simplex'' change throughout its four stages of development. However, these features have only been examined in detail in its third and fourth larval stages.Audicana, M. T., Del Pozo, M. D., Iglesias, R., & Ubeira, F. M. (2003) Anisakis simplex and Pseudoterranova decipiens. In M. D. Miliotis & J. W. Bier (Ed.), ''International Handbook of Foodborne Pathogens'', 633–656. Florida, United States: CRC Press. So4b-08

In its early stages, the

can be found in the faeces of its

, and is around 5mm in length, presenting a boring tooth and a bundle of sensory

nerves A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system. A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the e ...

at the front tip of its body.Nagasawa, K. (1990). The Life Cycle of Anisakis simplex: A Review. In H. Ishikura, & K. Kikuchi (Eds.), ''Intestinal Anisakiasis in Japan'', 31–40. Tokyo, Japan: Springer. Once it develops into a third stage larva, it grows to a length of 20 to 30 mm, and is found in the body cavity of the host, either freely floating or enclosed in a protective sac attached to the main organs. At this stage, the larva appears to be cylindrical with narrowed ends, and are visibly pink and white in colour, with a small white mark in the frontal region. Its outer surface is textured with irregular indents and striations.Ishii, Y., Fujino, T., & Weerasooriya, M. (1989). Morphology of Anisakine Larvae. In H. Ishikura, & M. Namiki (Eds.), ''Gastric Anisakiasis in Japan'', 19–29. Tokyo, Japan: Springer There are three protruding segments around the mouth that form the lips, one that is

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage * Dorsal co ...

and two that are ventrolateral, each with

lobules In anatomy, a lobe is a clear anatomical division or extension of an organ (as seen for example in the brain, lung, liver, or kidney) that can be determined without the use of a microscope at the gross anatomy level. This is in contrast to the m ...

on them. The two ventrolateral segments encase the triangular boring tooth and an excretory opening in front of it. The mouth then connects to the tubular esophagus that is visible from the frontal region and leads to the wideset ventriculus. A defining characteristic of this species is that the ventriculus is diagonally adjoined to the center of the intestine. At its rear end, the species has an anal opening, as well as spine-like structure known as the mucron. Third stage larvae develop into their fourth and last stage days after being ingested by their final host. In fourth stage larvae, the three lip segments are still present, but the dorsal segment has grown to be larger than the ventrolateral ones, and the boring tooth is no longer present within them. At the rear end, the mucron is replaced by a cone-shaped protrusion with small globular structures on it, and the previously irregular striations and indents on the outer surface of the organism become regularly patterned. At this stage, female larvae begin to develop reproductive organs at the center of their bodies, including internal

genitalia A sex organ (or reproductive organ) is any part of an animal or plant that is involved in sexual reproduction. The reproductive organs together constitute the reproductive system. In animals, the testis in the male, and the ovary in the female, ...

uteri The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The uteru ...

and surrounding

papillae Papilla (Latin, 'nipple') or papillae may refer to: In animals * Papilla (fish anatomy), in the mouth of fish * Basilar papilla, a sensory organ of lizards, amphibians and fish * Dental papilla, in a developing tooth * Dermal papillae, part of ...

Life cycle

There are four stages in the life cycle of ''A. simplex.'' The first stage includes emerging as an egg and hatching as larvae, and the following stages include being consumed by an intermediate host, a paratenic host, and lastly, a final host. The egg of the ''A. simplex'' is first found in the fecal matter of its final host in an unembryonated form, and is visibly transparent and circular, with an evenly-surfaced shell. Once they are passed,

embryos An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm c ...

begin to develop within these eggs until they grow into second-stage larvae. The egg then hatches, and second stage larvae emerge into the sea enclosed in a protective sheath.

The temperature of the water affects the speed of hatching of the eggs. In warmer temperatures, eggs take between 4 to 8 days to hatch, but in temperatures below 5°C, it may take up to 82 days. Once they are hatched, they can survive up to a month in warmer temperatures, and can last even longer in cooler temperatures below 10°C. However, the release of eggs from the final host is unaffected by seasonal factors or temperatures, so the rate of infection by the species is stable throughout the year. Once the eggs are hatched, second stage larvae are ingested by an intermediate host. This host is most commonly a

or some other type of marine

crustaceans Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean gr ...

. Upon ingestion, the larvae shed their protective sheath, then travel freely to the body cavity of the host to inhabit it. The change in the environment of the second stage larvae from the open water to the body of its host initiates their development into third stage larvae. The krill infected by third stage larvae are then ingested by common predators, such as squid and fish, specifically teleosts, who then become paratenic hosts. These hosts are referred to as paratenic because third stage larvae do not develop further when inhabiting them. At this stage, the larvae no longer roam freely in the gut of the host, but are rather embedded in their

viscera In biology, an organ is a collection of tissues joined in a structural unit to serve a common function. In the hierarchy of life, an organ lies between tissue and an organ system. Tissues are formed from same type cells to act together in a ...

, specifically in the mucus layers of the stomach, and eventually make their way into the inner muscles.Centre for Disease Control and Prevention DC (2019).
Anisakiasis
'. Retrieved April 17, 2021. Certain species of paratenic hosts are sold and consumed by humans, including salmon, mackerel,

cod Cod is the common name for the demersal fish genus '' Gadus'', belonging to the family Gadidae. Cod is also used as part of the common name for a number of other fish species, and one species that belongs to genus ''Gadus'' is commonly not c ...

anchovy An anchovy is a small, common forage fish of the family Engraulidae. Most species are found in marine waters, but several will enter brackish water, and some in South America are restricted to fresh water. More than 140 species are placed in 1 ...

sardine "Sardine" and "pilchard" are common names for various species of small, oily forage fish in the herring family Clupeidae. The term "sardine" was first used in English during the early 15th century, a folk etymology says it comes from the ...

and squids. ''Anisakis simplex'' reaches the end of its life cycle when the paratenic host is consumed by the final host, which are usually large marine mammals, such as whales,

dolphins A dolphin is an aquatic mammal within the infraorder Cetacea. Dolphin species belong to the families Delphinidae (the oceanic dolphins), Platanistidae (the Indian river dolphins), Iniidae (the New World river dolphins), Pontoporiidae (t ...

, and

seals Seals may refer to: * Pinniped, a diverse group of semi-aquatic marine mammals, many of which are commonly called seals, particularly: ** Earless seal, or "true seal" ** Fur seal * Seal (emblem), a device to impress an emblem, used as a means ...

. Here, the third stage larvae make their way into the abdomen of the host, and

moult In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is the manner in which an animal routinely casts off a part of its body (often, but not always, an outer ...

two times to become fully mature organisms. They then embed themselves into the mucus lining of the stomach, and produce digestive enzymes to ingest it. At this stage, the worms are able to

reproduce Reproduction (or procreation or breeding) is the biological process by which new individual organisms – "offspring" – are produced from their "parent" or parents. Reproduction is a fundamental feature of all known life; each individual org ...

. Females attract a mate by releasing chemical signals, and a male then wraps around a female to reproduce.

Distribution and habitat

The immediate habitat of ''A. simplex'' is within the body cavity of another marine animal, as it spends a majority of its life cycle being carried by these hosts. Its secondary habitats are the waterbodies in which these hosts reside. This includes the Pacific Ocean, the Atlantic Ocean, the

Arctic Ocean The Arctic Ocean is the smallest and shallowest of the world's five major oceans. It spans an area of approximately and is known as the coldest of all the oceans. The International Hydrographic Organization (IHO) recognizes it as an ocean, ...

and other regions characterised by cold marine waters. It is found along the coast and within the deeper regions of these waters. The geographical distribution of this species is inferred based on the rates of human infection in different locations. The first case of human infection was discovered in the

Netherlands ) , anthem = ( en, "William of Nassau") , image_map = , map_caption = , subdivision_type = Sovereign state , subdivision_name = Kingdom of the Netherlands , established_title = Before independence , established_date = Spanish Netherl ...

in the 1960s. Since then, cases have been detected in other parts of

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located enti ...

, including

Germany Germany, officially the Federal Republic of Germany (FRG),, is a country in Central Europe. It is the most populous member state of the European Union. Germany lies between the Baltic and North Sea to the north and the Alps to the sou ...

Spain , image_flag = Bandera de España.svg , image_coat = Escudo de España (mazonado).svg , national_motto = '' Plus ultra'' ( Latin)(English: "Further Beyond") , national_anthem = (English: "Royal March") , ...

Italy Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical ...

and the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the European mainland, continental mainland. It comprises England, Scotlan ...

.Audicana, T. & Kennedy, M. (2008). Anisakis simplex: from Obscure Infectious Worm to Inducer of Immune Hypersensitivity. ''Clinical Microbiology Reviews'', ''21''(2), 360–379. It has also been found in

Egypt Egypt ( ar, مصر , ), officially the Arab Republic of Egypt, is a transcontinental country spanning the northeast corner of Africa and southwest corner of Asia via a land bridge formed by the Sinai Peninsula. It is bordered by the Med ...

Korea Korea ( ko, 한국, or , ) is a peninsular region in East Asia. Since 1945, it has been divided at or near the 38th parallel, with North Korea (Democratic People's Republic of Korea) comprising its northern half and South Korea (Republi ...

and parts of the America, such as

Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only ...

Alaska Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U.S ...

and

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the souther ...

. However, it is most commonly detected in Japan. The main factors affecting the distribution and survival of this species are salinity and average sea surface temperature. While higher temperatures reduce the time taken for their eggs to hatch, it also reduces their chance of long-term survival.Kuhn, T., Cunze, S., Kochmann, J., & Klimpel, S. (2016). Environmental variables and definitive host distribution: a habitat suitability modelling for endohelminth parasites in the marine realm. ''Scientific Reports, 6''(1), 30246–30246. However, higher

salinity Salinity () is the saltiness or amount of salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensionless and equal ...

predicts longer survival times. Its distribution is also determined by locality, as it is specific to the aforementioned areas.Quiazon, K., Yoshinaga, T., & Ogawa, K. (2011). Distribution of Anisakis species larvae from fishes of the Japanese waters. ''Parasitology International, 60''(2), 223–226.

Health implications

''A. simplex'' can cause

zoonotic A zoonosis (; plural zoonoses) or zoonotic disease is an infectious disease of humans caused by a pathogen (an infectious agent, such as a bacterium, virus, parasite or prion) that has jumped from a non-human (usually a vertebrate) to a human. ...

diseases. The consumption or management of raw seafood puts humans at risk for developing an infection or allergic reaction caused by ''Anisakis simplex''. The presence of a single worm in a human’s body is enough to cause infection and elicit symptoms. In fact, this species is responsible for the majority of human infection cases within its family. Although such infections can be transmitted from animals to humans, it is not transmissible from one human to another.

Anisakiasis

Anisakiasis ''Anisakis'' (a·nuh·saa·keez) is a genus of parasitic nematodes that have life cycles involving fish and marine mammals. They are infective to humans and cause anisakiasis. People who produce immunoglobulin E in response to this parasite m ...

occurs when a parasitic worm, such as ''A. simplex,'' latches onto and penetrates the stomach or intestinal lining of a human, causing an infection. The infection is classified as

gastric The stomach is a muscular, hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital organ in the digestive system. The stomach i ...

, intestinal, or ectopic based on the site of the

lesion A lesion is any damage or abnormal change in the tissue of an organism, usually caused by disease or trauma. ''Lesion'' is derived from the Latin "injury". Lesions may occur in plants as well as animals. Types There is no designated classif ...

caused by the worm. A diagnosis is made based on an endoscopy of the relevant organs, or a

histopathological Histopathology (compound of three Greek words: ''histos'' "tissue", πάθος ''pathos'' "suffering", and -λογία ''-logia'' "study of") refers to the microscopic examination of tissue in order to study the manifestations of disease. Spec ...

examination of the affected tissue through surgery if the worm has already penetrated the walls of the organ and is not directly visibly anymore. Acute symptoms, such as abdominal cramps, nausea, fever, diarrhoea, and bloating begin to appear within a few hours of ingestion and signals the onset of gastric anisakiasis. This infection is often mistaken for another illness, such as a

peptic ulcer Peptic ulcer disease (PUD) is a break in the inner lining of the stomach, the first part of the small intestine, or sometimes the lower esophagus. An ulcer in the stomach is called a gastric ulcer, while one in the first part of the intestines ...

food poisoning Foodborne illness (also foodborne disease and food poisoning) is any illness resulting from the spoilage of contaminated food by pathogenic bacteria, viruses, or parasites that contaminate food, as well as prions (the agents of mad cow disea ...

, because they share common symptoms. Occasionally, people can sense the tingling of the worm in their oesophagus directly after ingestion, and can vomit to expel it from their body and prevent infection. However, if the worm reaches the stomach, it uses its protruding lip segments to penetrate the gastric

mucosa A mucous membrane or mucosa is a membrane that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue. It is ...

, and releases tissue-dissolving enzymes to eventually make its way into the

submucosa The submucosa (or tela submucosa) is a thin layer of tissue in various organs of the gastrointestinal, respiratory, and genitourinary tracts. It is the layer of dense irregular connective tissue that supports the mucosa (mucous membrane) and ...

. If left untreated, the infection can become chronic and cause symptoms such as dull stomachaches,

indigestion Indigestion, also known as dyspepsia or upset stomach, is a condition of impaired digestion. Symptoms may include upper abdominal fullness, heartburn, nausea, belching, or upper abdominal pain. People may also experience feeling full earlier ...

and vomiting that lasts for months. A typical endoscopy of the acute gastric form shows a worm embedded within the submucosa, with a visible lesion at the site of entry, and a thicker oedematous stomach lining. In patients with chronic gastric infection, there is often an ulcer or inflamed mass visible on the stomach lining. Intestinal anisakiasis can be detected approximately one week after ingestion. Similar to the gastric form, the terminal

ileum The ileum () is the final section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms posterior intestine or distal intestine m ...

bears a lesion through which the larva has penetrated into the submucosa. The intestinal lining becomes inflamed and can triple in its thickness, swollen masses are present, and the lumen becomes constricted. Ectopic anisakiasis occurs when the larvae bores through the

gastrointestinal The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans and ...

lining entirely, and travels to the surrounding organs in the abdominal cavity. It may even travel back to the oesophagus, where it can be regurgitated from the body.

Allergic reaction

Allergic reactions to ''A. simple''x can arise in combination with a gastrointestinal infection, or on its own. The first sign of a reaction arises within the hour of consumption, but its severity varies for each individual. Some people experience mild

urticaria Hives, also known as urticaria, is a kind of skin rash with red, raised, itchy bumps. Hives may burn or sting. The patches of rash may appear on different body parts, with variable duration from minutes to days, and does not leave any long-lasti ...

, while others experience

anaphylaxis Anaphylaxis is a serious, potentially fatal allergic reaction and medical emergency that is rapid in onset and requires immediate medical attention regardless of use of emergency medication on site. It typically causes more than one of the follo ...

or other clinically significant symptoms that can impair the functioning of the digestive,

cardiovascular The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...

and several other body systems. ''A. simplex'' is responsible for a majority of allergic reaction cases in adults who just consumed seafood. An allergy to ''A. simplex'' is diagnosed on the basis of three outcomes: a history of allergic reactions to seafood, the confirmation of relevant antibodies in an

in vivo Studies that are ''in vivo'' (Latin for "within the living"; often not italicized in English) are those in which the effects of various biological entities are tested on whole, living organisms or cells, usually animals, including humans, and ...

in vitro ''In vitro'' (meaning in glass, or ''in the glass'') studies are performed with microorganisms, cells, or biological molecules outside their normal biological context. Colloquially called "test-tube experiments", these studies in biology and ...

test, and the absent role of fish proteins.Audicana, M., Ansotegui, I., De Corres, L., & Kennedy, M. (2002). Anisakis simplex: dangerous - dead and alive? ''Trends in Parasitology, 18''(1), 20–25.

Epidemiology

Rates of human infection are highest in regions where raw or undercooked fish is commonly consumed. For example, the frequent consumption of ceviche in South America, smoked

herring Herring are forage fish, mostly belonging to the family of Clupeidae. Herring often move in large schools around fishing banks and near the coast, found particularly in shallow, temperate waters of the North Pacific and North Atlantic Ocea ...

in the Netherlands, and pickled anchovies in Spain poses a high risk of infection in these regions. Although dishes such as

sushi is a Japanese dish of prepared , usually with some sugar and salt, accompanied by a variety of , such as seafood, often raw, and vegetables. Styles of sushi and its presentation vary widely, but the one key ingredient is "sushi rice," also ...

and sashimi are now consumed globally, Japan remains the country with the highest number of cases. 95% of global anisakiasis cases come from Japan.

Treatment

The worm is often removed during the gastrointestinal endoscopy, which alleviates the symptoms within hours. However, surgical removal of the affected tissue must be conducted when the worms are already buried deep in the viscera. The allergic symptoms caused by ''A. simplex'' can be alleviated by anti-histamines, or other treatments that are commonly used for allergies.

Prevention

The elimination of raw or semi-cooked seafood is the most effective prevention method. According to

FDA The United States Food and Drug Administration (FDA or US FDA) is a federal agency of the Department of Health and Human Services. The FDA is responsible for protecting and promoting public health through the control and supervision of food s ...

guidelines, seafood should be cooked at a temperature of at least 63° C, and fish should be stored at a maximum temperature of -20°C for 7 days or -35°C for 15 hours for safe consumption. However, the

allergens An allergen is a type of antigen that produces an abnormally vigorous immune response in which the immune system fights off a perceived threat that would otherwise be harmless to the body. Such reactions are called allergies. In technical t ...

in ''A. simplex'' cannot be removed by heating or freezing processes.