Without knowing specifically what the bug was, it is difficult to point at a treating option. There are certainly many different types of ailments, including bacterial, fungal and parasitic. The majority of the problems encountered in the aquarium are bacterial in nature and a good full spectrum antibiotic will do the trick. In all honesty, I rarely use any medications. A series of water changes and the addition of some aquarium salt nearly always do the trick.
A note on feeders. These fish are mss produced with absolutely no culling involved. They are extremely inbred and are maintained in horrid conditions so it is no surprise that the majority of them have something tagging along with them. This is why, as a rule, feeders should be avoided. If there is an alternative, such as frozen, freeze dried or pelleted foods that your fish will take, these are much preferred. Some fish just won't take dead food though. In this case, a quarantine tank should be used where feeders are housed for several weeks before being fed. This gives the weak ones time to either die or shed whatever may be ailing them. You can treat this tank if you see fit, but heavy water changes as well as the addition of some salt should do the trick of clearing them up.