From your post information and not having caught the suspected "parasite" myself would not worry about it. It's pretty normal for wild creatures to carry parasites in them. Rarely due these parasites become a danger like in our enclosures where their numbers can become abnormally high and affect the host. As long as your pond's frogs are healthy and growing, would not worry about it.

Know of no tadpole parasites that would leave it's host through the mouth when they become froglets. There are some pond parasite treatments safe for frogs. Unless you have solid evidence the pond has a parasite problem, medicating it just in case, is not recommended. Good luck and post pics of your pond and frogs when possible !