Frogs can be infected with the plerocercoid (intermediate larval) stage of a cestode species from the genus Spirometra of tapeworms. These larva are acquired through ingestion of an invertebrate intermediate host and subsequently encyst in frogs tissue. Specifically, Spirometra erinacei encysts in the muscle and lymph tissue of the rear legs leading to fluid retention and the noticeable edema. The frog serves as a 2nd intermediate host (paratenic=transfer) host, after which it is eaten by a mammalian predator where it becomes an adult tapeworm and thus completes the life cycle. Unfortunately, once infected there is little hope for the frog.
Furthermore, it is a cruel industry, and shouldn't exist.
Also, they are nasty, and it's a gay thing to do.
That is all.
Don't eat frog's legs.