Eating untreated food definitely has a potential for parasites of infection. Treatment could be heating or freezing for the correct time and temperature, or some other method (pickling or salting I imagine might work to some extent.)
Getting infected or a gaining a parasite without eating will typically require not only the presence of the invasive organism, but a cut or abrasion, or some incidental ingesting of water. That does happen. (The son of a friend of mine caught a parasite, likely when he swallowed a small amount of water while swimming, in a Montana lake.) It was so rare (in California anyway) that it took weeks for them to identify why the boy was ill and not responding to antibiotics.
So I'd say uncommon or rare, but certainly possible. People who keep native species that they personally acquire from lakes and rivers might be a bit more at risk. Same would likely apply to people who routinely fish, manage fish farms, handle fish at markets, etc.
