If my birds ever got gapeworm, I'd cull them. It would be tough though.... it is what it is.Are your birds unwell? Are any underweight? Some level of worm burden is okay for many birds, and as long as they are in that environment, they will be reinfected often/ always.
Fenbendazole is the only wormer approved for use in chickens in the USA, and how it's dosed depends on the parasites present. It will kill one type of tapeworm, but not most species.
We have over thirty chickens right now, and daily individual dosing, for five or ten days straight, repeated three weeks later, isn't going to happen here (gapeworm treatment). Our university poultry expert told me that it isn't worth doing for my flock.
Aquasol is the fenbendazole that actually works when added to their drinking water as directed, wonderful! It is expensive, and we haven' bought it yet. Going together with a couple of other local poultry owners would make the price more 'user friendly', which is my plan.
Mary