Medical Research Council - London Institute of Medical Sciences

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Parasite Prevalence

Rise in the prevalence of the human-affecting parasitic worm Anisakis in wild fish

28 April 2020

Parasite Prevalence

Severe abdominal pain, nausea, vomiting and diarrhoea are the possible symptoms of anisakiasis – a parasitic gastrointestinal tract infection caused by eating raw or undercooked fish or squid containing Anisakis larvae (like the one pictured on this salmon fillet). Cooking kills these worm larvae, as does freezing, which is a recommended treatment for fish that are to be eaten raw, such as sushi or ceviche. However, under certain freezing conditions (not cold enough or long enough) the larvae may survive. Worryingly, recent research indicates that prevalence of Anisakis in wild fish is increasing. Indeed, one study indicates there has been a 243-fold increase in abundance – based on the number of worms found per fish – since the 1970s. Workers in the fish processing industry may be well-practiced in spotting and removing Anisakis larvae, but for concerned consumers it probably wouldn’t hurt to double-check their sushi for these 2cm-long wiggly menaces.

Written by Ruth Williams

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