These are also called threadworms (ie Enterobius vermicularis) and I studied them at uni. AND had to deal with repeat infestations.
What I remember being told at uni - these things are almost impossible to eradicate from the house, so (as with nits) we often tend to exhaust ourselves with practices that really do absolutely nothing (or very little) to prevent. My uni professor said that the eggs can even blow around in the dust in the house for up to two weeks. Of course, the eggs DO have to get from that dust into the mouth.
Some intestinal worms are really nasty. This one is perhaps one of the least nasty, all it does is make the child uncomfortable (sometimes) at night when trying to sleep - the classic "itchy bottom". Some kids will sleep through it.
What we found with our kids - most of them were VERY sensitive to "itchy bottom" and would come and wake me up so I could take a look. You can't see the worms at bedtime, generally - they don't come out until a few hours past bedtime. And you have very little chance of seeing them in the morning.
The life cycle of these things - we swallow the eggs, the eggs hatch out in our GI tract, the worms live and grow inside but right near the end and once sexually mature, they mate inside and the females crawl out the anus to lay their eggs. This tickles and disturbs the kids, who scratch, transferring the eggs onto their fingers and under fingernails. The eggs can be picked up by using a piece of stickytape pressed to the child's anus. We never did that except when studying them at uni. A pathologist might ask you to do this to confirm an infestation. You need a microscope and frankly, late at night you generally do see the worms. You can do what we did, and look with a torch - these things are really tiny, like half inch lengths of white sewing thread only slightly shinier. They do move (which can look really gross) but do absolutely no harm to the child other than making them uncomfortable and lose sleep. Standing in the bathroom with a Maglite pointed at your child's upturned rear end is not my favourite way to spend the hour after I went to bed, but it has to be done. You may need a magnifying glass and to get in really close. Don't think about how it looks, just do it. Plan to laugh later, maybe at the child's 21st birthday party. An Sensory Integration Disorder (SID) kid can REALLY freak out with these and be really badly affected. on the other hand, some other kids won't even notice - these are the kids who cause repeat infestations which will sweep through a classroom repeatedly, and through the families of the infected kid.
We used to have an ad on Aussie TV which showed a kid passing a pencil to another kid in class, with the caption, "She has just given him worms."
These things are VERY contagious, so it is a good thing they don't do any damage. If you are uncertain, or if other members of the family are also complaining of "itchy bottom, especially in bed at night" then dose everybody, all at the same time.
So if you've successfully identified that your child has a case, it's easy to treat. We kept a supply of commercial worm pills, if a kid had a dose we dosed the kid, immediately, and every other family member. Don't worry about the pets.
The next major preventive is hand washing, which has to INCLUDE scrubbing under the fingernails. Especially the infected person. Or use a nail file regularly (before each meal).
At school - it's so easy to transfer this. An infected kid can pass this on as easily as a cold. At a younger age kids tend to have more physical contact with each other and be more familiar with each other's personal space. The eases as they get older and this is also when repeat threadworm infestations ease. Until then, emphasise the importance of handwashing before eating, and keeping hands out of the mouth as much as possible, unless you are certain your hands (and nails) are clean. An infected child usually reinfects themselves via the fingernails.
Washing the rear end thoroughly in the morning and putting on clean clothes should reduce reinfestation (and spread to others) during the day. Someone suggested baby wipes - brilliant idea, we use them a lot too.
We did find that maintaining closer attention to handwashing, and cleaning nails of the infected child we did much better at preventing further infestations.
Washing bedding, pyjamas etc - the eggs will mostly stay on the skin, or on the fabric next to the skin. So if you make your child wear underwear under their pyjamas, then you only need to change those undies and not the pyjamas or the bedding. Regular, frequent (ie 'normal' underwear/pyjamas changing is all that's needed, but you SHOULD change clothing etc once you've begun treatment. Hot water wash and hang the stuff outside to dry. Don't bother until you've begun to treat the child, because the next night will only produce more eggs. Cleaning madly may make you feel better but by that stage you're probably only going to exhaust yourself. By not kicking up too much dust, you're also not spreading it round the house. The eggs WILL die eventually - takes about two weeks though, unlike nits which die in a matter of hours at room temperature. But you CAN open up the room to let the light in - the eggs die in strong sunlight.
Here is a good link on the topic. Once you know how these beasties grow and develop, it's just a matter of common sense.
http://www.cdc.gov/ncidod/dpd/parasites/pinworm/factsht_pinworm.htm
If you want to find more info, plug the scientific name into Google.
And having a child with threadworm is NOT an indication that you are unclean people - if so, then half the population would fit this category!
If he won't wash his hands, then all you can do is do it for him. Make sure his fingernails are short and try to get him to clean them, if there is any fingernail left to clean. File his nails smooth if he is a nail biter- that's another way to get threadworm back - biting nails. Make him change his underwear daily and wash his rear end in the mornings (you could always threaten to do it for him!). This is where you SHOULD use something disposable to wash his tail.
But if he's a real pain in the neck about it, just dose him and forget. And keep stocks of more treatments, because he WILL get reinfected.
If you know that you can hold him down ONCE, and clean him all over - then do that the morning after the first pill of the treatment. After that, reinfestation will be from wherever he's getting it elsewhere, and not his own body.
Aren't our difficult children charming? Is is any wonder this beastie affects half the population?
Marg