Rennie, who specializes in fish dishes, said large tuna varieties such as blue fin, yellow fin and big eye are usually parasite-free. But Rennie said trout, cod and wild small salmon such as sockeye and coho (not king salmon) are prone to parasites.
In fact many grocery stores sell fish that's been through "candling" to remove surface parasites.
"They put fillets on glass and shine strong light through and pick it out worms with tweezers," she said. "They do that so you don't go to back to [the store] and rip the fishmonger's head off."
Disgusting as parasites may sound, fish safety officials, parasitologists and cooks say most of us should relax. It only takes cooking the fish to kill off the parasites.
"I always hear, 'oh my god, I'll never cook fish again -- but if you have ever eaten a fish dish before you, I promise you have eaten parasites before," said Rennie. "But if you are serving it raw at home -- I don't suggest anybody do that without any real training."
According to U.S. Food and Drug Administration regulations, all fish meant to be served as sushi must be frozen for a specified period of time (usually a week) to kill lurking parasites.
Rennie said no matter how fresh, unless you're buying certified "sushi grade" fish it's best not to try to serve it raw at home.
"Parasites are really a non-issue, it's not as big of a problem as time and temperature holding," said Pamela Tom, Seafood Network Information Center Director at the University of California, Davis. "People focus on methyl mercury, but in reality it's not as important as the bacteria."
"I'd say overall the nation is not at risk," she said.
Indeed, many other countries still see fish tapeworm more often than the raw-fish aficionados in the United States.
"There was one big recall a couple years ago in California where someone brought in fresh salmon from up north to a restaurant," said Scott Lyell Gardner, curator and professor at the Harold W. Manter Laboratory of Parasitology at the University of Nebraska - Lincoln.
"People get it very commonly, especially in the northern parts of the world -- in Norway, Finland, Canada," he said.
Gardner said the fish tapeworm naturally moves from larval stages in fish to adult stages in bears (or sea mammals). The large mammals then excrete the eggs back into the water to start the process all over again.
"The main life cycle is bear-salmon, bear-salmon, and people get into it when they eat salmon," he said. Bottom line: cooking makes the fish safe. To stop this cycle, cook your fish."