According to the Seafood Network Information Center at UC Davis, "The health risk from parasites [in raw fish] is far less than the risk from 'unseen' illness causing bacteria which are present on almost all foods." (http://seafood.ucdavis.edu/Pubs/paras...)
As was noted above, almost all sashimi-grade fish is flash-frozen, and freezing kills the parasites. Moreover, even if you get a live parasite in your fish, it probably won't attach itself to your digestive tract, but will instead pass through unnoticed. And any that do stick around die within a few days, since humans aren't optimal hosts. So the worst-case scenario is nasty--but non-life-threatening--stomach bug that resolves itself in a couple of days with rest and plenty of fluids.
My take on it? People who are extremely risk-averse shouldn't eat raw fish. But unless you're the type who bleaches your lettuce, the risk posed by nematodes is minimal compared to that posed by other foods in your diet.
Having read all the responses, it surprises me that so few are worried about acquiring parasites from eating sushi. A number of years ago Craig Claiborne wrote a column in the NYT about sushi and in the article he mentioned that parasites were the number-one public health problem in Japan. He related examples of parasitic infections or infestations, one of which entailed the worms wriggling up the esophagus and into the mouth of the diner (though this particular organism did not live in the body and other than the objectionable worms in the mouth was otherwise harmless). Ever since reading that I have restricted my sushi eating to only cooked fish or vegetables, even though prior to reading the article I was a fanatic and frequent consumer of all types of sushi.
I am not an authority, but I think all fish can have parasites of some sort.
I once made ceviche with fresh cod. After adding lime juice, visible worms came wriggling outta the flesh. Were these worms (which were parasitic to the cod) dangerous to me? I would guess that my intestinal track would have did them in, but the ceviche no longer seemed appealing, so the question was never quantified...
Yeah, steer clear of freshwater sushi or ceviche, as chin master points out, there's no freshwater fish on sushi menus for a reason.
I would somewhat agree with your last statement, queen, that most parasites cannot adapt to humans.
One of our friends was directed not to eat sushi while she was pregnant because of parasitic dangers. It was the first I heard of this and was surprised, but I guess a fetus has a compromised immune system as three of us points out.
Finally, I wouldn't let the fear of parasites prevent you from enjoying sushi, thats for sure! I think the fear far outweighs the realities - kinda like the fear of a car accident preventing you from driving. (actually, I'd probably get in a car accident going out for sushi...)
Don't know about sushi in particular but I was told by a friend who is an infectious disease doc that a healthy human immune system can kill off parasites found in raw fish/meats or undercooked meats. A compromised immune system ( can mean everything from serious illness like AIDS to being run down and having a cold) may not be able to rid the body of parasites so it is best to avoid uncooked foods.
While they may not "adapt"to human hosts, there have been news stories (not urban legends) about them sending people to the hospital for emergency surgery, at least with home-prepared fish. Supposedly, restaurant chefs are adept at identifying the culprits and getting rid of them.
There is "sushi-grade: fish for sale; but then again, there is much "wild salmon" for sale that is farm-raised.
Part of what a sushi chef does while preparing the food is inspect for freshness, parasites, etc. In the US "sushi grade" is handled to reduce the risk of parasites. The term can be loosely used, so question your fish source to be sure that the fish is meant to be eaten raw. This site has some good info:
There have been threads about this in the past that had some good details & insights!
The parasites present in fish are in their gut. The life cycle of these worms is that once an animal dies the parasites sense this and move out of the gut, through the intenstinal walls and into the flesh in preparation to be eaten.
When a fish is caught and processed immediately (gutted) virtually all chance of this happening disappears.
Further, most fish that is called Sushi Grade is flash frozen at sea, which also kills virtually all of these parasites that might have snuck in there. When in doubt, excellent sushi chefs will check a very thin slice (think of a piece of lox) and hold it up to the light ... the worms are large enough to be visible.
These worms are not the common tape worms that humans have been plagued with for millions of years. The Anisakiasis larvae can come from ceviche or sushi. They can cause nausea, vomiting, cramps, abdominal pain and intestinal gas. It will usually pass though (and it's highly likely that most cases of infection go unreported because they resolve themselves).
It is safe to eat saltwater fish raw, however, eating raw freshwater fish is not so much.
Think on it for a moment, there is no trout or carp (or other freshwater fish offered on sushi menus) for a reason. These eggs and parasites will survive the GI tract and make life "interesting". I believe that it is osmotic shock that does marine parasites in the GI tract.
Salmon and eel do not count as freshwater because move between fresh and saltwater, however, I would not be eating either raw while the young had yet to migrate out into the ocean -after they come back into freshwater, acquired marine parasites die and they are safe.