Food System

Parasites in farmed fish, new EFSA opinion

April 22, 2024

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The risks related to the presence of zoonotic parasites in farmed fish and the appropriate measures to inactivate them are addressed in the opinion published by EFSA (European Food Safety Authority) on 22 April 2024. (1)

Parasites in farmed fish, EFSA Opinion 2010

The previous scientific opinion of EFSA’s BIOHAZ Panel (2010) reviewed the following conclusions:

– parasitic diseases transmitted from fish to humans are mainly caused by infection with viable parasites cestodes, trematodes and nematodes, although allergic reactions are also possible when the parasite is Anisakis simplex (sensu lato)

– freezing (e.g. core temperature of -15°C for at least 96 h, or at -20°C for 24 h, or at -35°C for 15 h) and heat treatments (e.g. core temperature of at least 60°C for at least 1 minute) are the most effective for killing fish-borne parasites, including their larvae

– there is insufficient information to assess whether alternative treatments such as high pressure (HPP), irradiation, drying and low voltage currents are suitable for killing Anisakidae larvae

– many traditional marinating and cold-smoking methods are not sufficient to kill larvae.

New EFSA opinion (2024)

The European Commission asked EFSA to update its 2010 BIOHAZ scientific opinion on the following aspects:

– presence of parasites of public health significance in fishery products derived from the most common farmed fish species in the EU (e.g. Atlantic salmon, sea bass, farmed sea bream and turbot)

– diagnostic methods for the detection of parasites of health significance in fishery products derived from these farmed fish species

– technical developments and new scientific data available in relation to the elimination of parasites in fishery products by treatments other than thermal killing, and

– possible health risks related to the presence of parasites in certain wild fish species caught in specific fishing grounds.

Fishery products, consumption in the EU

Aquaculture in the EU currently produces around 1.1 mln tonnes of aquatic organisms with a value of EUR 4.2 bn/year.

Annual fish production in the non-EU countries Norway and Iceland (EFTA), the UK and the Faroe Islands is just over 2 mln tonnes, with Norway in first place (1.66 mln tonnes). Atlantic salmon (species Salmo salar, ‘salmon’) is by far the dominant species.

The average annual per capita consumption of fishery products in the EU is around 24 kg, of which a quarter (around 1.25 mln t) comes from aquaculture.

The four most consumed fish in the EU are:

– tuna (all species together, mostly wild)

– salmon (mostly farmed)

– cod (mostly wild)

– Alaska pollack (wild).

Aquaculture, the most widespread species in Europe

Production and consumption data identify the 18 most widespread farmed fish species in the EU and EFTA countries, therefore considered in this opinion.

Marine aquaculture:

– Atlantic salmon (Salmo salar, ‘salmon’)

– rainbow trout (Oncorhynchus mykiss)

– sea bream (Sparus aurata)

– sea bass (Dicentrarchus labrax)

– bluefin tuna (Thunnus thynnus)

– turbot (Scophthalmus maximus/Psetta maxima)

– yellowtail flounder (Argyrosomus regius)

– halibut (Hippoglossus hippoglossus)

– northern cod (Gadus morhua)

– amberjack (Seriola dumerili).

Freshwater breeding:

– rainbow trout (Oncorhynchus mykiss)

– brown trout (Salmo trutta)

– carp (Cyprinus carpio)

– eel (Anguilla anguilla)

– sheatfish (Silurus glanis)

– African catfish (Clarias gariepinus)

– tench (Tinca tinca)

– pikeperch (Sander lucioperca).

Parasites transmissible to humans

The most important zoonotic – i.e. transmissible to humans – parasites in farmed fish produced in EU and EFTA countries include

– in the marine environment, the nematodes Anisakis simplex (sensu stricto), A. pegreffii, Phocanema decipiens (sensu lato) and Contracaecum osculatum (sensu lato) as well as the trematode Cryptocotyle lingua

– in freshwater ecosystems, the trematodes Opisthorchis felineus, Metorchis spp., Pseudamphistomum truncatum, Paracoenogonimus ovatus and the cestode Dibothriocephalus spp.

Parasites in farmed fish

Fish from land-based recirculating seawater aquaculture systems or in indoor or covered rearing facilities with filtered and/or treated water and fed exclusively with pelleted feed are unlikely to be exposed to zoonotic parasites.

Conversely, fish reared in open offshore sea cages or in open-flow freshwater ponds or tanks may be exposed to zoonotic parasites.

Studies on the presence of parasites in fish are few in number, completely absent for five fish, and mainly analyse anisakids, in most cases with negative results. (2)

Bibliographic review

The exception is the evidence found on four fish:

– European sea bass. Two of the 10 studies reported two larvae of A. pegreffii and two of A. simplex (s.l.) in three fish, in one case also in fillet

– bluefin tuna. A. pegreffii and A. simplex (s. s.) were detected with prevalence values ranging from 17.1 % to 32.8 %

– Atlantic cod. Presence of C. lingua and A. simplex (s. l.), with a prevalence of 55-79% for the former and 1% for the latter

– tench. Potentially zoonotic freshwater trematodes (P. ovatus and P. truncatum) were detected.

No cestodes (Dibothriocephalus spp.) were found in studies on farmed fish in Europe.

Intercepting parasites in fish products

In recent years, new technologies and methods have been developed for the detection, visualisation and isolation of zoonotic parasites in fish products and for the specific identification of isolated parasites. These include:

UV scanning devices for the detection of Anisakis in fishery products
optical (hyperspectral) detection methods
in the testing phase, the application of artificial intelligence and machine learning algorithms in image and video processing to support high-throughput detection
the prediction of the presence and identification of parasites in fishery products generated by omics (genomics, metagenomics, transcriptomics and proteomics). A recent and useful resource for the selection of additional molecular/genetic markers to be used for the identification and characterisation of zoonotic parasites.

Research and innovation are essential to develop the indicated tools, which can be applied on a large scale following further development and validation.

EFSA zoonoses database

The EFSA database of Member State communications on zoonoses and food-borne outbreaks reports on 11 human food-borne outbreaks caused by unspecified Anisakis spp. between 2010 and 2022.

One case occurred in France in 2010, the other 10 in Spain between 2014 and 2020 (1,2,3). In contrast, no outbreaks were reported to EFSA in 2021 and 2022.

Overall, 45 cases of the disease were reported with two hospitalisations and no deaths. Four outbreaks were reported with clear evidence concerning the food vehicle, i.e. ‘fish and fishery products’.

Anisakis, an underestimated problem

In Italy, researchers have reported more than 50 cases of disease caused by A. pegreffii (Matteucci et al., 2018; Guardone et al., 2018; D’Amelio et al., 2023) since 1999.

Three recent cases have been reported in Portugal, in 2017 and 2018, reported by Santos et al., 2022 (1,2).

The incidence of human Anisakiasis, according to researchers, is underestimated due to problems with diagnosis.

How to kill parasites in fishery products

In 2010, EFSA’s BIOHAZ Panel evaluated a dozen methods proposed as useful for killing parasites in fishery products.

Freezing, the limits of the household freezer

Freezing is effective in killing parasites in fish. The lower the freezing temperature, the shorter the time it takes to kill parasites. For example, at -10°C anisakids can survive for a few days, while at -35°C the survival period is reduced to a few hours.

It is essential that all parts of the fish reach a lethal temperature, and maintain it for as long as necessary. Bear in mind that domestic two-star freezers (which operate between -6°C and -12°C) are not suitable for freezing fish to kill nematode parasites.

Heat treatment

Cooking at least 60°C at the core of the product for 1 minute, 15 seconds at 74°C, is sufficient to neutralise all anisakid larvae in fishery products. The time to reach this temperature inside the product is influenced by its thickness.

High pressure treatment

High pressure treatment (HPP) can kill A. simple larvae. In some fish species, effective combinations to kill A. simplex larvae (414 MPa for 30-60 s; 276 MPa for 90-180 s; 207 MPa for 180 s) have, however, caused changes in the colour and appearance of muscles that may limit the application of this technology. Treatment at 300 MPa for 5 minutes could in any case be effective in treating mackerel and other fatty fish species, according to EFSA.

Techniques still unconfirmed

Drying and ultrasound have not yet proven their effectiveness in inactivating parasite larvae.

Irradiation is ineffective against A. simplex, which resists it at doses acceptable for fishery products (up to 3 kGy). It is, however, sufficient at low doses to inactivate or prevent metacercariae infectivity of O. viverrini and C. sinensis in freshwater fish.

Low-voltage current to inactivate A. simplex larvae in fish, although promising, is still lacking adequate scientific studies.

Smoking, salting and marinating

Traditional treatments of fish products are variously effective:

– hot smoking, at temperatures above 60°C for 3-8 hours, kills A. simplex,

– cold smoking, where temperatures are kept below 38°C for a few hours to several days, is unsuitable for inactivating A. simplex larvae,

– salting can inactivate anisakids, provided the salt concentration in the brine reaches 8%-9% and the fish are kept there for at least 6 weeks. In dry salting, 20 days are sufficient. Salting with 13.5% NaCl for 24 hours inactivates Opisthorchis metacercariae in fish,

– marinating some traditional products is not sufficient to kill A. simplex larvae, which, depending on the salt concentration, can survive from 35 to 119 days. It is therefore necessary to freeze the products before marinating.

Phytocompounds

In 2010, EFSA’s BIOHAZ Panel also reported the efficacy of certain photocompounds – such as shogaol and gingerol extracted from Zingiber officinale, components of Perilla leaves or monoterpene derivatives of essential oils (i.e. alpha-pinene) – to inactivate Anisakis.

The efficacy of these chemical treatments is, however, dependent on certain variables such as the size and fat content of the fish and the content of bioactive substances in the botanical extracts. It is therefore recommended to always combine these procedures with thermal killing.

The 2010 opinion of EFSA’s BIOHAZ Panel was taken into account for the amendment of Part D of Annex III, Section VIII, Chapter III of Regulation (EC) No 853/2004 (Commission Regulation (EU) No 1276/2011).

Provisional conclusions

Thermal killing and heating – under the conditions described above – remain the most effective and reliable methods for killing Anisakis larvae in fresh fishery products.

Innovative methods of parasite inactivation have been verified under laboratory conditions, but further research is needed to verify their effectiveness under commercial conditions:

pressure/time combinations used in industrial high pressure processing (HPP), in particular, could be applied on some specific products
pulsed electric field (PEF) is considered a promising technology, although further developments are needed. Furthermore,
the use of natural products could have some applications, although data on safety and organoleptic properties are still lacking.

Maria Ada Marzano and Dario Dongo

Footnotes

(1) Biological Hazards Panel EFSA. Re-evaluation of certain aspects of the EFSA Scientific Opinion of April 2010 on risk assessment of parasites in fishery products, based on new scientific data. Part 1: ToRs1-3. EFSA Journal https://doi.org/10.2903/j.efsa.2024.8719

(2) Studies that have tested for parasites in fish since 2010 concern salmon (4), rainbow trout (5), sea bream (9), sea bass (10), bluefin tuna (2), turbot (3), shad (1), halibut (1), Atlantic cod (1), freshwater rainbow trout (1), sheatfish (1), tench (1) and common carp (1). No studies are available for amberjack, brown trout, African catfish, European eel and pike perch.