I am unfamiliar with the ectoparasites you described, perhaps others will know. Chances are it was a pseudoparasite.
Releasing this frog due to parasites is not all logical. ANY food can be a source of parasites. ESPECIALLY live, wild caught animals. It is likely your snake is already loaded with parasites, you should be getting a parasite check at least twice a year. Your snake should taken off of a frog diet anyway. If it happens to be a hognose, they don't need frogs and subsist nicely on an all rodent diet.
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"I know the human being and fish can coexist peacefully."
Governor George W. Bush, Jr.
"Sometimes I think the surest sign that intelligent life exists elsewhere in the universe is that none of it has tried to contact us."
Calvin and Hobbes (Scientific Progress Goes 'Boink', 1991)