The known history of Anisakis begins with a serving of pickled herring at the port of Rotterdam in 1955. It might have become a very costly meal to the Dutch diner, suddenly suffering from severe abdominal cramps, had it not been for Dr. Van Thiel, who proceeded to perform an emergency laparotomy. The small intestine of the patient was obstructed as a result of the inflammation caused by a small worm about 2 cm long, lodged deep in the intestinal wall. Since then we have known anisakiasis as the disease caused by nematodes of the genus Anisakis, with several tens of thousands of confirmed cases diagnosed to date – and many others suspected. Patients refer acute or chronic digestive symptoms such as abdominal or stomach pain, nausea and moderate fever, diarrhea, hives and severe lifelong allergies. This disease is much more frequent among habitual consumers of raw, pickled or marinated seafood (tuna tartar, anchovies in vinegar, gravlax, cold smoked salmon, sashimi, etc.).
Bad luck, because this parasite is mainly hosted by marine mammals like dolphins, seals or whales. These excrete worm eggs that morph through several larval stages in crustaceans, saltwater or freshwater fish and cephalopods, until they are ingested again by the cetaceans, thus completing the Anisakis life cycle. When the human seafood lover gets in between, the savouring of delicacies such as hake, sardine, squid or octopus acquires a risky tinge. And it is a very ubiquitous bug, present from the Atlantic to the Pacific oceans, wandering through the Mediterranean sea and also including the Arctic and Antarctic waters. Anisakiasis is especially prevalent in coastal areas of Japan, Spain (Basque Country, Galicia and Andalusia), Italy or Morocco, but has also been detected in several African, American and Asian countries.
Although visual inspection does not offer great guarantees due to the size and location of the parasite inside the fish, technically it is not difficult to secure protection against infection by a thermal treatment (heat or cold) that inactivates the Anisakis larvae. In order to guarantee the safety of fish consumption, freezing at -20ºC for 24 h or a heat treatment at 60ºC for at least 10 min is mandatory according to European legislation (CE / 853/2004, RD / 1420/2006). However, the recent confirmation of several anisakiasis cases among frozen fish consumers, and the high incidence of the infestation (with parasite presence rates of up to 90% in hake, 80% in bonito, 70% in horse mackerel, 40% in sardines, crustaceans and cephalopods) are enforcing the rethinking of the strategies against this serious public health problem. Focus is now on the duration of the heat treatment (the North American FDA already recommends a minimum of 7 days) and on the control of the fishing discards that contribute to spread the infestation when dumped into the high seas.
The potential implications of parasitic diseases are highlighted when considering that the world consumption of fish has increased at a rate of 3.6% per year since 1961, doubling its demand in this period to reach 57 Kg per person per year in Portugal or 42 Kg in Spain. Because all wild fish, both fresh and salt water, are susceptible to host nematode parasites, an intense work has been carried out during these years in order to develop reliable tools for their rapid detection in fresh or processed fish and shellfish. Fortunately, today methods such as real-time PCR, UV fluorescence image analysis, Western blot or ELISA allow for the efficient and precise detection of Anisakis at moderate costs.
Perhaps those succulent mullet roe or seasoned tataki you just gobbled up might result in uncomfortable afterthoughts, prominently featuring the wandering marine worm. You will sleep peacefully though after feasting on cultured yellowtail, turbot, bream or sole, because aquaculture fish has been found to be generally parasite free. Anisakis infestations have rarely been detected in farmed Atlantic salmon (0.1%) or in Greek seabass (0.7%); more recently, the European project Parafishcontrol has shown the total absence of the bicho in thousands of seabream, seabass, turbot, salmon, trout and carp samples collected from European fish farms.
Although this is an issue currently being investigated, the absence of Anisakis and other parasitic worms in aquaculture fish appears to derive from the treatment (heat and pressure) that the raw materials making up the feed receive during manufacture. Aquaculture feed (extruded and or pelleted) is free of parasites, fungi and bacteria, ensuring the health of the animals throughout their production cycle in the fish farms. There is, however, some minimal risk in sites functioning as open systems using untreated water (cages, ponds, estuaries, etc.), because farmed animals can ingest small amounts of wild fish or crustaceans contaminated with the parasite. In any case, in addition to feed, it is clear that good management practices in European aquaculture, requiring high monitoring and control standards as in any animal production industry (water treatment, animal welfare, hygiene, prevention and surveillance) are those really responsible for the production of fish offering unmatched quality guarantees to an increasingly demanding and informed consumer.
So if you fancy a good night of sushi or a rich and spicy ceviche, or if you just feel like indulging in a tasting session of raw and/or fresh parasite-free seafood, consider the advantages of farmed fish, fasten your apron, relax and enjoy.