question: Why is it safe to eat some raw fish?
comment: Some of it wouldn’t be safe pulled straight out of the water. The part of the government in charge of food safety, the FDA, requires all fish intended to be served raw to be flash frozen. A technique that kills parasites and keeps the food fresh. The biggest risk of sushi in the US is from improper handling. Outside of the US, if unfamiliar with their food safety requirements then only eat saltwater fish raw. Not the fish that spend any time in fresh water. Tuna is best for avoiding parasites.
passages: People at high risk for infection have traditionally been those who regularly consume raw fish. Many regional cuisines include raw or undercooked food, including sushi and sashimi in Japanese cuisine, carpaccio di persico in Italian, tartare maison in French-speaking populations, ceviche in Latin American cuisine and marinated herring in Scandinavia. With emigration and globalization, the practice of eating raw fish in these and other dishes has brought diphyllobothriasis to new parts of the world and created new endemic foci of disease.
  
  Section::::Public health strategies.
   Parasite infection by raw fish is rare in the developed world (fewer than 40 cases per year in the U.S.), and involves mainly three kinds of parasites: Clonorchis sinensis (a trematode/fluke), Anisakis (a nematode/roundworm) and Diphyllobothrium (a cestode/tapeworm). Infection risk of anisakis is particularly higher in fishes which may live in a river such as salmon ("sake") in Salmonidae or mackerel ("saba"). Such parasite infections can generally be avoided by boiling, burning, preserving in salt or vinegar, or freezing overnight. In Japan it is common to eat raw salmon and ikura, but these foods are frozen overnight prior to eating to prevent infections from parasites, particularly anisakis.
   Section::::Eating raw fish.
  
  Though not a health concern in thoroughly cooked fish, parasites are a concern when human consumers eat raw or lightly preserved fish such as sashimi, sushi, ceviche, and gravlax. The popularity of such raw fish dishes makes it important for consumers to be aware of this risk. Raw fish should be frozen to an internal temperature of −20 °C (−4 °F) for at least 7 days to kill parasites. It is important to be aware that home freezers may not be cold enough to kill parasites.
   Parasites in fish are a natural occurrence and common. Though not a health concern in thoroughly cooked fish, parasites are a concern when consumers eat raw or lightly preserved fish such as sashimi, sushi, ceviche, and gravlax. The popularity of such raw fish dishes makes it important for consumers to be aware of this risk. Raw fish should be frozen to an internal temperature of −20 °C (−4 °F) for at least 7 days to kill parasites. Home freezers may not be cold enough to kill parasites.
   Parasite infection by raw fish is rare in the developed world (fewer than 40 cases per year in the U.S.), and involves mainly three kinds of parasites: Clonorchis sinensis (a trematode/fluke), Anisakis (a nematode/roundworm) and Diphyllobothrium (a cestode/tapeworm). Infection by the fish tapeworm "Diphyllobothrium latum" is seen in countries where people eat raw or undercooked fish, such as some countries in Asia, Eastern Europe, Scandinavia, Africa, and North and South America. Infection risk of anisakis is particularly higher in fishes which may live in a river such as salmon ("shake") in Salmonidae, mackerel ("saba"). Such parasite infections can generally be avoided by boiling, burning, preserving in salt or vinegar, or freezing overnight. Even Japanese people never eat raw salmon or ikura (salmon roe), and even if they seem raw, these foods are not raw but are frozen overnight to prevent infections from parasites, particularly anisakis.
   Parasites in fish are a natural occurrence and common. Though not a health concern in thoroughly cooked fish, parasites are a concern when consumers eat raw or lightly preserved fish such as sashimi, sushi, ceviche, and gravlax. The popularity of such raw fish dishes makes it important for consumers to be aware of this risk. Raw fish should be frozen to an internal temperature of −20 °C (−4 °F) for at least 7 days to kill parasites. It is important to be aware that home freezers may not be cold enough to kill parasites.
   Sashimi or other types of sushi containing raw fish present a risk of infection by three main types of parasites:
  
  BULLET::::- "Clonorchis sinensis", a fluke which can cause clonorchiasis
  
  BULLET::::- "Anisakis", a roundworm which can cause anisakiasis
  
  BULLET::::- "Diphyllobothrium", a tapeworm which can cause diphyllobothriasis
   Parasite infection by raw fish is rare in the developed world (fewer than 40 cases per year in the U.S.), and involves mainly three kinds of parasites: Clonorchis sinensis (a trematode/fluke), Anisakis (a nematode/roundworm) and Diphyllobothrium (a cestode/tapeworm). Infection risk of anisakis is particularly higher in fishes which may live in a river such as salmon ("sake") in Salmonidae or mackerel ("saba"). Such parasite infections can generally be avoided by boiling, burning, preserving in salt or vinegar, or freezing overnight. In Japan it is common to eat raw salmon and ikura, but these foods are frozen overnight prior to eating to prevent infections from parasites, particularly anisakis.
   Section::::Role in disease.:Control and treatment.
  
  Several measures can be taken to control infection in aquaculture once an "S. iniae" outbreak has been confirmed. Decreasing the quantity of feed given to fish has been shown to reduce mortality rates, as the uptake of bacteria in water is expedited by feeding. Decreasing the density of the fish stock increases survival by reducing injury to fish and lowering the general stress level in the population. Lowering the water temperature and keeping optimal oxygen levels has also been shown to reduce stress to fish and inhibit bacterial growth.
   List of raw fish dishes
  
  This article is about raw fish or shellfish. It includes marinated raw fish (soaked in a seasoned liquid) and raw fish which is lightly cured such as gravlax, but not fish which is fully cured (fermented, pickled, smoked or otherwise preserved).
  
  Section::::Health concerns.
   Traditionally, fish that live all or part of their lives in fresh water were considered unsuitable for sashimi due to the possibility of parasites (see sashimi article). Parasitic infections from freshwater fish are a serious problem in some parts of the world, particularly Southeast Asia. Fish that spend part of their life cycle in brackish or freshwater, like salmon are a particular problem. A study in Seattle, Washington showed that 100% of wild salmon had roundworm larvae capable of infecting people. In the same study farm raised salmon did not have any roundworm larvae.
   Because the toxins are very heat-resistant, consumers cannot protect themselves by cooking these contaminated fish. When fish are collected from certain areas known to contain these toxins and are mislabeled, consumers may be seriously injured. Although there is a treatment for the disease, the disease is not often properly diagnosed and the treatment is most effective if administered within 72 hours of exposure. Avoiding the species of fish known to contain the disease or avoiding eating fish from locations known to have the disease are the only preventative measures.
  
  Section::::Risks to the consumer.:Scombroid.
   Section::::Health implications.:Allergic reactions.
  
  Even when the fish is thoroughly cooked, "Anisakis" larvae pose a health risk to humans. Anisakids (and related species such as the sealworm, "Pseudoterranova" species, and the codworm "Hysterothylacium aduncum") release a number of biochemicals into the surrounding tissues when they infect a fish. They are also often consumed whole, accidentally, inside a fillet of fish.
   One parasite in fish was previously known as "Spironucleus barkhanus", but was then redescribed as "Spironucleus salmonicida". This new classification was given to this organism so that "Spironucleus salmonicida" could be discernible from the fish commensals "Spironucleus barkhanus" as they were morphologically identical, but genetically different ". Spironucleus vortens" species is often found in freshwater angelfish, where it affects the gastrointestinal tract and may cause head and lateral line erosion . Pathogenesis of "Spironucleus" can be promoted by stressful environmental conditions, including poor water quality, malnutrition, overcrowding, and fluctuating temperatures. These pathogens can be found in wild fish, as well as farmed fish. However, farmed fish are more susceptible to the "Spironucleus" pathogen due to the poor conditions that sometimes accompany aquaculture.
   Cooking or deep-freezing (-20 °C for 7 days) of food made of fish is sure method of prevention. Methods for prevention of "Opisthorchis viverrini" in aquaculture fish ponds were proposed by Khamboonruang et al. (1997).
  
  Section::::Treatment.
   According to recent studies, there have been about 18 million infections worldwide from eating raw fish. This serves as a great risk to expecting mothers due to the health risks that medical interventions or treatment measures may pose on the developing fetus. Parasitic infections can have a wide range of health impacts, including bowel obstruction, anemia, liver disease, and more. The impact of these illnesses alone can pose some health concerns on the expecting mother and baby, but the curative measures that may need to take place to recover, are also a concern as well.
   Toxin that is produced by the bacterium in containers of food that have been improperly preserved is the most common cause of food-borne botulism. Fish that has been pickled without the salinity or acidity of brine that contains acetic acid and high sodium levels, as well as smoked fish stored at too high a temperature, presents a risk, as does improperly canned food.
   Fish are subject to various viruses, bacteria and fungi in addition to parasites such as protozoans, flukes and worms, or crustaceans. These are naturally occurring in many bodies of water, and fish that are stressed for other reasons, such as spawning or suboptimal water quality, are more susceptible. Signs of disease include sores, missing scales or lack of slime, strange growths or visible parasites, and abnormal behavior–lazy, erratic, gasping at the water surface or floating head, tail or belly up.
   Some species of fish, notably the puffer fugu used for sushi, and some kinds of shellfish, can result in serious poisoning if not prepared properly. These fish always contain these poisons as a defense against predators; it is not present due to environmental circumstances. Particularly, fugu has a lethal dose of tetrodotoxin in its internal organs and must be prepared by a licensed fugu chef who has passed the national examination in Japan. Ciguatera poisoning can occur from eating larger fish from warm tropical waters, such as sea bass, grouper, barracuda, and red snapper. Scombroid poisoning can result from eating large oily fish which have sat around for too long before being refrigerated or frozen. This includes scombroids such as tuna and mackerel, but can also include non-scombroids such as mahi-mahi and amberjack. The poison is odourless and tasteless.
   There are many disease-carrying pathogens found in raw meats, and they differ according to the source, whether it be mammalian, poultry or seafood. Some disease-carrying pathogens found in beef are "Salmonellas", "Escherichia coli", "Shigella", "Staphylococcus aureus", and "Listeria monocytogenes". Different varieties of "Salmonellas" are often found in contaminated poultry. Seafood itself can also contain a wide variety of pathogens. The most common pathogen in raw oysters is "Vibrio" gastroenteritis, while "Salmonella", "Plesiomonsas shielloides", and "staphylococcus" are found in contaminated raw shrimp, and "Vibrio cholerae" has been found in raw crabmeat. Many of the symptoms that result from these diseases involve intestinal damage and can have potentially fatal effects for those at risk. The symptoms of an E. coli infection include bloody diarrhea, severe abdominal pain, and possible complications for the immune-compromised, elderly or children. These complications can include Haemolytic uraemic syndrome (HUS) and neurological problems. The symptoms of "Vibrio" gastroenteritis include frequent fevers, bloody diarrhea, long duration of illness and hospitalization. While most of these diseases are still most commonly found in raw meat, the instances of detection in other mediums are increasing. For instance, "Salmonella" is most commonly found in poultry, but has been recently identified in sources such as eggs, dairy, meat, fresh vegetables and fruits. E. coli has also been found in beef, lamb, lettuce, sprouts, fruit juices, vegetables, raw milk, and water. Possible reasons for the increase are the globalization of the food market, improper handling, and leakage.
   Scombroid food poisoning is syndrome resembling an allergic reaction that occurs within a few hours of eating fish contaminated with scombrotoxin. Scombroid poisoning derives its name from the family of fish most commonly associated with the disease, the Scombridae family (tuna, mackerel, skipjack and bonito). Fish outside Scombridae have been found to cause scombroid fish poisoning, including mahi mahi, bluefish, marlin, and escolar. When these fish are not refrigerated properly, bacteria can metabolize naturally occurring histamines in these fish to produce scombrotoxin. To prevent illness in these species of fish, ensuring the proper storage conditions of the fish from water to plate is of utmost importance. Freezing, cooking, smoking, curing and/or canning do not destroy Scombroid toxins. Thus, lack of proper species knowledge can make it difficult to ensure proper storage conditions both for suppliers and consumers of fish.
   Section::::Risks to the consumer.:Ciguatera.
  
  A very common foodborne illness in fish is ciguatera, which is caused by eating certain reef fishes whose flesh is contaminated with toxins. The CDC states the following about Ciguatera:
   Diagnosis is based on a person's symptoms together with having recently eaten fish. If a number of those who eat the same fish have symptoms the diagnosis becomes more likely. If some of the fish they had previously eaten is available this can also be tested to confirm the diagnosis. Other potential causes such as paralytic shellfish poisoning (PSP), neurotoxic shellfish poisoning (NSP), scombrotoxin fish poisoning, and pufferfish poisoning should be excluded.
  
  The reversal of hot and cold sensations is an occasional symptom of CFP that may help differentiate it from intestinal "flu".
  
  Section::::Treatment.
   Pathogens which can cause fish diseases comprise: 
  
  BULLET::::- viral infections, such as esocid lymphosarcoma found in "Esox" species.
  
  BULLET::::- bacterial infections, such as "Pseudomonas fluorescens" leading to fin rot and fish dropsy
  
  BULLET::::- fungal infections
  
  BULLET::::- water mould infections, such as "Saprolegnia" sp.
  
  BULLET::::- metazoan parasites, such as copepods
  
  BULLET::::- unicellular parasites, such as "Ichthyophthirius multifiliis" leading to ich
  
  BULLET::::- Certain parasites like Helminths for example "Eustrongylides"
  
  Section::::Parasites.
   Two years after the first 10 cases of human infection with "N. salmincola" were reported in 1987, Fritsche et al. reported ten additional cases of human nanophyetiasis. Five presented with gastrointestinal complaints and the other five had unexplained peripheral eosinophilia. Nine out of ten recalled eating inadequately cooked fish. This time, praziquantel was the effective treatment of choice.
  
raw_presuppositions: It is safe to eat some raw fish.
raw_corrections: It is not safe to eat raw fish unless it is flash frozen or pulled straight out of saltwater.