Anisakidae and Anisakidosis: A Public Health Perspective

Abstract

Fish and seafood are increasingly recognised as safe and nutritiously valuable foods of animal origin, being a source of about 17% of animal protein globally. Novel culinary trends encourage the consumption of raw or thermally lightly processed fishery products. At the same time, consumers prefer wild, fresh and whole fish over farmed or processed fish. However, the consumption of raw or undercooked fish and other marine organisms poses a risk of contracting parasitic infections, potentially representing a public health risk. Among the most common seafoodborne parasites are members of the Anisakidae family, especially the genus Anisakis, which can cause potentially detrimental effects to human health. These parasites are the causative agent of a zoonosis termed anisakidosis that is prevalent in countries with high per capita fish consumption. Although the number of annual clinical cases varies among countries and regions and is generally not high, sensitisation to this parasite in the general population seems to be considerably higher. Therefore, anisakidosis is still significantly underreported and misdiagnosed globally, making it a disease of rising public health concerns. To prevent infection and mitigate potential negative effects on human health, proper preventive measures such as gutting the fish, freezing or thermal processing are needed. Moreover, a holistic approach implementing One Health principles together with educational campaigns towards the general public and primary care physicians can extend the knowledge on the occurrence of these parasites in their natural hosts and the diagnosis and incidence of anisakidosis, with a final goal to minimize risks for human health and reducing costs for health systems.

Keywords: Anisakis; Contracaecum; Phocanema; anisakidae; anisakidosis; public health.

Figure 1

The number of publications (bottom) and citations (top) per year in the last decade (including 2024) in the Scopus database related to Anisakidae.

Figure 2

Percentage of studies related to Anisakis sensitisation in different populations included in systematic review by Mazzucco et al. [18] and published afterwards. Note that some studies included more than one population. General asymptomatic population refers to subjects not occupationally exposed to Anisakis allergens and without history of symptoms related to anisakidosis.

Figure 3

Percentage of different serodiagnostic tests used in studies related to Anisakis sensitisation.

Figure 4

The general life cycle of anisakid nematodes. Gravid females release their eggs into the water column with the faeces of the final host (1), where they are embryonated (2). After two moults, the eggs hatch into free-swimming third-stage larvae (L3) (3), which are ingested by an intermediate host (crustacean) (4). In the intermediate host, the larvae migrate to the haemocoel and become infective. The intermediate host is then eaten by a paratenic host (fish, squid), in which the larvae spiralise in the visceral organs or the musculature (5). Small fish can be eaten by larger fish. In this case, the larvae repeat the process of migration and spiralisation (solid arrow) and can accumulate in large numbers. Alternatively, intermediate host can be eaten directly by the final host (e.g. baleen whales) (dashed arrow). The life cycle is completed when the intermediate/paratenic host is eaten by a final host, i.e., a toothed whale, a pinniped or a fish-eating bird, depending on the anisakid genus, in which the L3 develop into L4 (subadult) and sexually mature adults (6). In the life cycle of anisakids, humans can become accidental hosts after eating raw or lightly thermally processed seafood infected with anisakids L3. i—infective stage, d—diagnostic stage.

Figure 5

Anisakis spp. spiralised (black arrows) on visceral organs and actively moving in the visceral cavity (white arrows) of blue whiting, Micromesitius poutassou. (Photo credit: Jerko Hrabar).

Figure 6

The morphology of the third larval stage of Anisakis spp. (L3), larval type I (sensu Berland, 1961). (a) The cephalic end with a small pyramidal boring tooth (arrow); (b) the anterior part with a dark-coloured ventriculus (arrow). Note that in living specimens the ventriculus appears as a white, barrel-shaped structure that is clearly visible to the naked eye; (c) a tail with a small spine (mucron) at the tip of the tail (arrow). (Picture credits: Jerko Hrabar).

Figure 7

A world map showing the documented distribution of zoonotic species of Anisakidae in the period 1986–2018. Two Antarctic species of the Contracaecum osculatum complex, i.e., C. osculatum D and C. osculatum E, are not indicated on the map (adapted from [13,26]).

Figure 8

Morphology of Phocanema spp., third larval stage (L3). (a) Cephalic end with small pyramidal boring tooth (arrow); (b) anterior part with ventriculus and anteriorly projecting intestinal caecum (arrow); (c) detail of image in panel B showing intestinal caecum (arrow); (d) posterior end. (Picture credits: https://www.cdc.gov/dpdx/anisakiasis/ (accessed on 7 September 2024)).

Figure 9

Morphology of Contracaecum spp., third larval stage (L3). (a) Cephalic end showing the oesophagus (oe), ventriculus (v), intestinal caecum (ic) and ventricular appendix (va); (b) detail of cephalic region showing boring tooth (arrow) and nerve ring (nr); (c) detail of ventriculus with clearly visible ventricular appendix running along dark-stained intestine; (d) posterior end with intestine (i) opening into rectum (r) and anus (a) and tail without spine (mucron). (Picture credits: [78]).

Figure 10

A histological section of a paraffin-embedded eosinophilic granuloma with four cross-sections of the third larval stage (L3) of Anisakis spp. Polymyarian muscle cells (thin arrows) are divided into four quadrants by two Y-shaped lateral chords (arrowheads). Two cross-sections show a banana-shaped excretory gland cell (Renette cell) (thick arrows), which is located ventrally to the intestine. (Picture credits: [123]).

Figure 11

Blue fluorescence third larval stage of Anisakis spp. exposed to UV light. (a) Anisakis spp. larvae on fish gonads; (b) larvae (yellow circles) in pressed and frozen fish fillets (picture credits: Vida Šimat and Jerko Hrabar).