I discovered that my 4 year old had threadworms on Friday night, treated the whole family on Saturday morning, changed and hoovered all the beds and sat back smugly thinking that I had the critters sorted ...I have been checking his bottom a couple of times a day over the weekend and today I noticed what looked like a number of dead worms plus a couple of wrigglers. Do I need to re-treat everyone so soon after the initial dose? Does it really take days for these things to die off??