Great you found the old thread!
Permethrin, I guess I wasn't thinking fleas, but there may be other tiny parasites, like mites (storage mites in kibble, dust mites, scabies, etc). Don't know if there are other critters that might be susceptible.
I guess the question is how much of the anti-fungal is helping, and how much of the anti-parasite is helping? Definitely not something you know right now, unless you have tried an anti-fungal alone with no success.
I do not know if the current flea and tick meds with permethrin in them would be as effective as the creme. There may some natural products that contain similar ingredients.
Ivermectin *i think* usually helps scabies, so I'm a bit confused about why this works and the ivermectin didn't, unless there is a strong fungal component, or a bug that is resistent.