I'm not sure that you can really inspect for all possible parasites (intestinal parasites, for example). Bacteria and fungi are also possible issues. Some experts seem in favor of fish as feeders, and argue that most frogs carry some parasite load anyway, which is not an issue under normal circumstances. In addition, many parasites are host-specific. Personally, I think that Dubia and nightcrawlers are a reasonable alternative to fish. Breeding your own fish might also be safer...