Anisakis

Aibinu, Ibukun E., Smooker, Peter M. & Lopata, Andreas L., 2019, Anisakis Nematodes in Fish and Shellfish- from infection to allergies, International Journal for Parasitology: Parasites and Wildlife 9, pp. 384-393 : 385

2. Anisakis biology and life cycle

The definitive host of anisakid, where the adult stage of the parasite is found, are cetaceans, (marine mammals such as dolphins and seals). Eggs of the parasite are passed with faeces of definitive host into the marine environment where they hatch and develop into the 2nd stage larvae of the parasite (Baird et al., 2014; Buchmann and Mehrdana, 2016). The larvae that develop from the eggs are eaten by the intermediate hosts, crustaceans (copepods, decapods, isopods, amphipods, euphausiids) and molluscs (Baird et al., 2014). It is well established that one of the most important first intermediate hosts in the Anisakis life cycle are the Euphasiids (Krill) (Smith and Wootten, 1978). Infected krill eaten by fish or squid become a source of the infective 3rd stage larvae of Anisakis for the paratenic hosts (fish or squid). The Anisakis larvae encyst on the intestines and other visceral organs of these hosts. The parasite does not develop further and remains at the third stage of larvae development (L3 stage) in these hosts. The life-cycle comes to a completion when infected fish/squid are eaten by marine mammals such as whales, seals and dolphins. In these definitive hosts, the larvae grow to the L4 stage and subsequently to the adult stage ( Fig. 1 ). The nematode feeds, grows, mates and then releases eggs via the host faeces into the sea water to continue its life cycle (Pozio, 2013). As is common with parasites with complex life cycle, the morphology of Anisakis varies with the different stages and infected hosts. In fish, the L3 stage larvae displays a coiled shape, which when uncoiled, is about 2 cm long. Humans become accidental hosts when undercooked or raw fish and cephalopods, contaminated with the parasite are consumed.

Figures

Fig. 1. Anisakid Life Cycle. Location of the L3 larvae may be gastric, intestinal or ectopic.