Is possible for people to get tapeworms from ahi tuna?

In theory yes, it seems that big fish caught off Alaska can harbour the tapeworm Diphyllobothrium nihonkaiense see That Sushi May Contain a Tract-Invading Parasitic Tapeworm But according to http://abcnews.go.com/Health/GlobalHealth/story? read more

Sushi grade tuna is all required to have been frozen at one point or another because the freezing process kills the worms, making them perfectly okay to ingest. We could get the most gorgeous piece of tuna in, and not be able to sell it as sushi grade if it has not been frozen. The more you know. read more