There is a spray on that you can get from most feed type stores. "Blue Cote" I think it is. It is for screw worms and is specifically used when we dehorn the cattle. What our vet has done when we had to dehorn an older cow that decided to start hooking the other cows for some reason, is to stuff it with cotton soaked in an iodine solution. It will come out usually in a few days or we have taken it out after about 3-4 days, but it allows some air into it while keeping out stuff like hay and dirt/dust.
I save the cotton that comes in medicine bottles, like in aspirin or some vitamins, and keep it in a covered tupperware type container til I need it.
But anything that says good for screw worms, should do the job.