| Anisakis | |
|---|---|
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| Anisakis simplex | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Nematoda |
| Class: | Chromadorea |
| Order: | Rhabditida |
| Family: | Anisakidae |
| Genus: | Anisakis Dujardin, 1845 |
| Species | |
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Anisakis (/ænəˈsɑːkiːz/a-nə-SAH-keez) is agenus ofparasiticnematodes that have life cycles involving fish andmarine mammals.[1] They are infective to humans and causeanisakiasis. People who produceimmunoglobulin E in response to this parasite may subsequently have an allergic reaction, includinganaphylaxis, after eating fish infected withAnisakis species.
The genusAnisakis was defined in 1845[2] byFélix Dujardin as a subgenus of thegenusAscarisLinnaeus,1758. Dujardin did not make explicit theetymology, but stated that the subgenus included the species in which the males have unequalspicules ("mâles ayant des spicules inégaux"); thus, the nameAnisakis is based onanis- (Greek prefix for different) andakis (Greek for spine or spicule). Two species were included in the new subgenus,Ascaris (Anisakis)distansRudolphi, 1809 andAscaris (Anisakis) simplex Rudolphi, 1809.[citation needed]
Anisakis species have complexlife cycles which pass through several hosts through the course of their lives. Eggs hatch in seawater, andlarvae are eaten by crustaceans, usuallyeuphausids. The infectedcrustaceans are subsequently eaten by fish or squid, and thenematodes burrow into the wall of thegut andencyst in a protective coat, usually on the outside of thevisceral organs, but occasionally in themuscle or beneath theskin. The life cycle is completed when an infected fish is eaten by a marine mammal, such as awhale,seal,sea lion,dolphin or another animal like aseabird orshark. The nematode excysts in the intestine, feeds, grows, mates, and releases eggs into the seawater in the host'sfeces. As the gut of a marine mammal is functionally very similar to that of a human,Anisakis species can infect humans who eat raw or undercooked fish.[citation needed]
Sexual reproduction occurs once the larvae have reached a definitive host and completed their final molt, at which point sexual organs are developed.[3] Females are capable of producing 2.6 million eggs, depending on species and size at sexual maturity.[4]
The knowndiversity of the genus has increased greatly since mid-1980s with the advent of moderngenetic techniques inspecies identification.[5] Each final host species was discovered to have its own biochemically and genetically identifiable "sibling species" ofAnisakis, which is reproductively isolated. This finding has allowed the proportion of different sibling species in a fish to be used as an indicator ofpopulation identity in fish stocks.[citation needed]
Anisakis share the common features of all nematodes: thevermiform body plan, round incross section, and a lack ofsegmentation. The body cavity is reduced to a narrowpseudocoel. Themouth is locatedanteriorly and surrounded by projections used in feeding and sensation, with theanus slightly offset from theposterior. Thesquamous epithelium secretes a layeredcuticle to protect the body from digestive acids.[citation needed]
As with all parasites with a complex life cycle involving several hosts, details of the morphology vary depending on the host and life cycle stage. In the stage that infects fish,Anisakis species are found in a distinctive "watch-spring coil" shape. They are roughly two centimeters long when uncoiled. When in the final host, anisakids are longer, thicker, and more sturdy, to deal with the hazardous environment of a mammalian gut.[citation needed]
 | It has been suggested that this section besplit out into another article titledAnisakiasis. (Discuss)(January 2024) |
Anisakids pose a risk to human health through intestinal infection with worms from the eating of underprocessed fish and through allergic reactions to chemicals left by the worms in fish flesh.[6]
| Anisakiasis | |
|---|---|
 | |
| Differential symptoms of parasite infection by raw fish:Clonorchis sinensis (trematode/fluke),Anisakis (nematode/roundworm) andDiphyllobothrium (cestode/tapeworm),[7] all have gastrointestinal, but otherwise distinct, symptoms.[8][9][10][11] | |
| Specialty | Infectious disease |
Anisakiasis is a human parasitic infection of the gastrointestinal tract caused by the consumption of raw or undercooked seafood containing larvae of thenematodeAnisakis simplex.
Within a few hours of ingestion, the parasitic worm tries to burrow through the intestinal wall, but since it cannot penetrate it, it gets stuck and dies. The presence of the parasite triggers an immune response; immune cells surround the worms, forming a ball-like structure that can block thedigestive system, causing severe abdominal pain, malnutrition, and vomiting. Occasionally, the larvae are regurgitated. If the larvae pass into the bowel or large intestine, a severeeosinophilicgranulomatous response may also occur one to two weeks following infection, causing symptoms mimickingCrohn's disease.[12][13] Anisakiasis may present as a gastric, intestinal, or allergic disease.[14]
The first case of human infection by a member of the family Anisakidae was reported in the Netherlands by Van Thiel, who described the presence of a marine nematode in a patient suffering from acute abdominal pain.[15] It is frequently reported in areas of the world where fish is consumed raw, lightly pickled, or salted. The areas of highest prevalence are Scandinavia (fromcodlivers), Japan (after eatingsashimi), the Netherlands (by eating infectedfermented herrings (maatjes), Spain (from eating anchovies and other fish marinated inescabeche), and along the Pacific coast of South America (from eatingceviche). The frequency in the United States is unknown because the disease is not reportable[citation needed] and can go undetected or be mistaken for other illnesses. Anisakiasis was first recognized in the 1960s.During the 1970s, about 10 cases per year were reported in the literature. The frequency is probably much higher, due to home preparation of raw or undercooked fish dishes. In Japan, more than 1,000 cases are reported annually.[16] Development of better diagnostic tools and greater awareness has led to more frequent reporting of anisakiasis.
Diagnosis can be made by gastroscopic examination, during which the 2-cm larvae are visually observed and removed, or by histopathologic examination of tissue removed at biopsy or during surgery.[citation needed]
Important clues for the diagnosis of anisakiasis include a recent history of eating raw or insufficiently cooked fish or squid followed by the sudden start of epigastric or right lower quadrant stomach pain. The removal and examination of the larva by gastroscopy or surgery provides a definitive diagnosis.[17]
Raising consumer and producer awareness about the existence of anisakid worms in fish is a critical and effective prevention strategy. Anisakiasis can be easily prevented by adequate cooking at temperatures greater than 60 °C[citation needed] or freezing. The FDA recommends all shellfish and fish intended for raw consumption be blast frozen to −35 °C or below for 15 hours or be regularly frozen to −20 °C or below for seven days.[16] Salting and marinating will not necessarily kill the parasites, as in Italy where two-thirds of cases were attributed toanchovies marinated in lemon or vinegar.[18] Humans are thought to be more at risk of anisakiasis from eating wild fish rather than farmed fish.[citation needed] Many countries require all types of fish with potential risk intended for raw consumption to be previously frozen to kill parasites. The mandate to freeze herring in the Netherlands has virtually eliminated human anisakiasis in the Netherlands.[19]
The best preventive measure for Anisiakis is to avoid eating raw or undercooked fish or squid.[20] Another common prevention method is the thermal treatment of the fish or squid prior to consumption. The fish or squid should be cooked at >60 °C for >1 min or frozen whole at −20 °C for >24 h.[21]
For the worm, humans are a dead-end host.Anisakis andPseudoterranova larvae cannot survive in humans, and eventually die. In some cases, the infection resolves with only symptomatic treatment.[22] In other cases, however, the infection can lead tosmall bowel obstruction, which may require surgery,[23] although treatment withalbendazole alone (avoiding surgery) has been reported to be successful.Intestinal perforation (an emergency) is a possible complication.[24]
Even when the fish is thoroughly cooked,Anisakis larvae pose a health risk to humans. Anisakids (and related species such as the sealworm,Pseudoterranova species, and the codwormHysterothylacium aduncum) release manybiochemicals into the surrounding tissues when they infect a fish. They are also often consumed whole, accidentally, inside a fillet of fish.[citation needed]
Acute allergic manifestations, such asurticaria andanaphylaxis, may occur with or without accompanying gastrointestinal symptoms. The frequency of allergic symptoms in connection with fish ingestion has led to the concept of gastroallergic anisakiasis, an acute IgE-mediated generalized reaction.[15] Occupational allergy, including asthma, conjunctivitis, and contact dermatitis, has been observed in fish processing workers.[25]sensitization and allergy is determined by skin-prick test and detection of specific antibodies againstAnisakis. Hypersensitivity is indicated by a rapid rise in levels ofIgE in the first several days following consumption of infected fish.[15] A 2018 review of cases in France has shown that allergic cases were more commonly found, although the number of humanAnisakis infections was decreasing.[26]
Larval anisakids are common parasites of marine and anadromous fish (e.g.salmon,sardine), and can also be found in squid and cuttlefish. In contrast, they are absent from fish in waters of low salinity, due to the physiological requirements ofkrill, which are involved in the completion of the worm's life cycle.Anisakids are also uncommon in areas wherecetaceans are rare, such as the southernNorth Sea.[27] Due to having complex life cycles, species-specific relationships and their eggs being released in the feces of their definitive host, the identification of anisakids in local fish populations can be a useful tool in assessing the range or migratory patterns of their definitive host.[28]
Unusual hosts ofAnisakis larvae in theSouthern Hemisphere, rarely reported, includeseabirds,sharks, orsea kraits.[29]
There are currently 13 species known to exist in this genus, with 12 formally described and one additional species given a temporary name (A. simplex sensu Davey, 1971 is a temporary name). There are three additional species classified astaxon inquirendum (A. dussumierii (Brenden, 1870),A. insignis (Diesing, 1851), andA. salaris (Gmelin, 1790) Yamaguti, 1935). There is one another species classified as nomen dubium (A. diomedeae (Linstow)). An additional 17 species names are now currently considered synonyms for the 13 species believed to exist in this genus.[30]
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