Anisakis and anisakiasis

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It seems that we are facing a new disease, anisakiasis. Anisakiasis is a public health problem, which incidence has increased recently. Humans are accidental hosts that become affected via the ingestion of anisakis larvae present in raw or undercooked fish and seafood. Preventive measures are essential to control the disease.

What is anisakis?

Anisakiasis is a parasitic disease caused by anisakis nematodes (free-living, non-segmented, cylindrical worms) that can invade the stomach wall or intestine of humans. The transmission of this disease occurs when infective larvae are ingested from fish or squid that humans eat raw or undercooked. In some cases, this infection is treated by removal of the larvae via endoscopy or surgery. The best ways to prevent this disease is to avoid eating raw or undercooked fish or squid.
How does one become infected?
When certain infected marine mammals (such as whales or sea lions) defecate into the sea, eggs are released and become infective larvae while in the water. These larvae are ingested by crustaceans, which are then eaten by fish or squid. When humans eat raw or undercooked infected fish or squid, they ingest nematode larvae. Once inside the human body, the larvae can invade the gastrointestinal tract. Eventually, the parasite dies and produces an inflamed mass in the esophagus, stomach or intestine.

Some raw or practically raw fish preparations that have to be frozen before consumption in order to prevent anisakis. 

•    Anchovies in vinegar and other soused fish.         
•    Sashimi, sushi, carpaccio and other specialties based on raw fish.    
•    Marinated fish, for example, ceviche.  
•    Fish roe only if raw or practically raw. 
•    Herring and other raw fish prepared in brine.         
•    Smoked fish of the following species: herring, mackerel, sprat and salmon (wild) from the Atlantic or the Pacific.        
Products that do not cause the disease even if they are consumed raw without prior freezing
•    Oysters, mussels, clams, and other bivalve mollusks.                
•    Fish habituating continental waters (such as rivers, lakes and reservoirs) and freshwater fish farms. This is the case of such fish as trout and carp.
•    Semi-preserves, such as anchovies (in metal cans or glass jars or in other packaging). 
•    Salt-dried fish, such as cod and salted tuna fish.   

What are the signs and symptoms?

Some people experience a tingling sensation after or while eating raw or undercooked fish or squid. This is actually the worm moving in the mouth or throat. These people can often extract the worm manually from their mouth or cough up the worm and prevent infection. Also, some people experience vomiting as a symptom and this can often expel the worm from the body.  
The signs and symptoms of anisakiasis are abdominal pain, nausea, vomiting, abdominal distention, diarrhea, blood and mucus in stool, and mild fever. Allergic reactions with rash and itching, and infrequently, anaphylaxis, can also occur.

How can we prevent anisakiasis?

The FDA recommends the following for seafood preparation or storage to kill parasites.
•    Cooking (Seafood in General)
o    Cook seafood adequately (to an internal temperature of at least 145° F [~63° C]).
•    Freezing (Fish) 
o    At -4°F (-20°C) or below for 7 days (total time), or
o    At -31°F (-35°C) or below until solid, and storing at -31°F (-35°C) or below for 15 hours, or
o    At -31°F (-35°C) or below until solid and storing at -4°F (-20°C) or below for 24 hours.

Preventing infection in humans
•    Avoid eating raw fish dishes. When cooking fish, cook for a minimum of five minutes at 60 degrees Celsius or a shorter time at higher temperatures.
•    Buy fish clean and gutted. If it is not gutted, do so yourself as soon as possible.  
•    It is preferable to use farmed fish for raw dishes as these fish appear to be virtually free of infection.
•    Traditional cooking of fish (boiled, fried, baked or grilled) eliminates the parasite.
•    These traditional methods of preparing fish allow the entire piece to be cooked at a temperature of 60ºC, which guarantees total safety.
•    If you eat raw or practically raw fish, freezing it before consumption is the most effective procedure to kill the parasite. If fish is to be eaten raw, it should preferably be frozen at -30 degrees Celsius.
•    Marinating or smoking the fish will not necessarily kill anisakis.
•    It must be frozen at a temperature of – 20º C or less for at least 24 hours.
•    Refrigerators with fewer than 3 stars (***) do not reach the desired temperature to carry out this procedure.      
•    Home refrigerators having 3 stars (***) or more require more time to reach this temperature than an industrial refrigerator, therefore you are recommended to freeze fish at a temperature of – 20º C or less over a period of 7 days. 

Which are the countries where anisakiasis cases are more common?
Anisakiasis is most commonly found in areas where eating raw fish is popular. These are the countries where anisakiasis cases are more common: Japan (for the consumption of raw fish which has not been frozen previously, such as sashimi or sushi), South American areas where “ceviche” is popular, Scandinavia (because of parasites in cod) and in The Netherlands (by eating herring in poor condition).  Spain appears also to have the highest reported incidence in Europe and marinated anchovies are recognized as the main food vehicle.

Read 5077 times Last modified on Thursday, 08 February 2018 13:57

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