Humans are thought to be more at risk of anisakiasis from eating wild fish rather than farmed fish. 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. Allergic reactions
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 codworm Hysterothylacium aduncum) release a number of biochemicals into the surrounding tissues when they infect a fish. They are also often consumed whole, accidentally, inside a fillet of fish. Acute allergic manifestations, such as urticaria and anaphylaxis, 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. Occupational allergy, including asthma, conjunctivitis, and contact dermatitis, has been observed in fish processing workers. Sensitivization and allergy are determined by skin-prick test and detection of specific antibodies against Anisakis. Hypersensitivity is indicated by a rapid rise in levels of IgE in the first several days following consumption of infected fish. A 2018 review of cases in France has shown that allergic cases were more commonly found, although the number of human Anisakis infections was decreasing. Treatment
For the worm, humans are a dead-end host. Anisakis and Pseudoterranova larvae cannot survive in humans, and eventually die. In some cases, the infection resolves with only symptomatic treatment.
The nematode excysts in the intestine, feeds, grows, mates, and releases eggs into the seawater in the hosts feces. As the gut of a marine mammal is functionally very similar to that of a human, Anisakis species are able to infect humans who eat raw or undercooked fish. Reproduction
Sexual reproduction occurs once the larvae have reached a definitive host and completed their final molt, at which point sexual organs are developed. Females are capable of producing 2.6 million eggs, depending on species and size at sexual maturity.The known diversity of the genus has increased greatly since mid-1980s with the advent of modern genetic techniques in species identification. Each final host species was discovered to have its own biochemically and genetically identifiable "sibling species" of Anisakis, which is reproductively isolated. This finding has allowed the proportion of different sibling species in a fish to be used as an indicator of population identity in fish stocks. Morphology
Anisakis share the common features of all nematodes: the vermiform body plan, round in cross section, and a lack of segmentation. The body cavity is reduced to a narrow pseudocoel. The mouth is located anteriorly and surrounded by projections used in feeding and sensation, with the anus slightly offset from the posterior. The squamous epithelium secretes a layered cuticle to protect the body from digestive acids. As with all parasites with a complex life cycle involving a number of hosts, details of the morphology vary depending on the host and life cycle stage.