one way to tell is if you cant gain wieght no matter what you do, roundworms keep you from gaining or even sometimes losing wieght. Alot of people say you can gain wieght with worms, everybody I know with worms has lost wieght lol even my dog, i find it hard to believe the whole gain weight from worms statement.
Other ways you can tell if you still have roundworm are: loud stomach noises, clear mucuos in stool (even hard formed stool), gas and bloating.
Or you can order a DNA stool test from MetaMetrix.com, tests your stool NOT for eggs and parts BUT for the DNA of the worms.HOPE THIS HELPS