I have an eight-year-old patient with recurring pinworms. I haven’t run a stool workup on her yet, though I plan to. Up to this point, her family has treated her a few times with conventional OTC pinworm remedies, which seem to work, but then she becomes reinfected. A pharmacist told them they need to wait six months before treating. She has some developmental delays, which make proper handwashing more unlikely than usual, although they do the best they can. They’re particularly concerned because the pinworms migrate to her vulva and cause a lot of discomfort, and there’s a potential association with pinworms and pelvic inflammatory disease. Can you speak about pinworms and the old friends hypothesis and treatment other than what is available conventionally?

Chris Kresser: OK, so there are a few different questions in here. Starting with the end first, the old friends hypothesis, as many of you know, suggests that there are certain organisms that human beings coevolved with and that may actually play an important role in helping to regulate our immune system and therefore eradicating them if their natural residence of our gut may not be a good idea. Hookworm, Necator americanus, is one, and some have speculated that pinworms could play that role, but the difference between hookworm and pinworms, and one of the defining characteristics of an “old friend,” meaning one of these commensal organisms that benefits us, but doesn’t harm us, is that it doesn’t cause harm. Hookworm certainly can cause harm if we’re harboring really large amounts of them, and so it no longer qualifies as an old friend there, and pinworms, if they’re causing extreme discomfort and migrating to the vulva and potentially triggering PID, then certainly they’re not an old friend at all, and they should be dealt with.

In terms of how to deal with them, it’s been a while since I looked into this, but when I did, if I’m recalling this correctly, using Pin-X, which is available over the counter, or mebendazole, if you do a single dose and you follow it up with another dose a couple of weeks later, which addresses the lifecycle of the pinworm, the efficacy is much higher than if you just do the single dose. It’s hard to know exactly how to advise because I’m not sure which OTC remedies she used in this case, but the other thing to consider is what’s the overall gut ecosystem like? When we see recurrent gut infections, especially with commensal organisms or with organisms like pinworm that can be passed back and forth, the question is, why is that patient so susceptible to those infections? That’s something that should certainly be on your mind here because if she has gut flora that makes her gut a hospitable environment and doesn’t allow her to fight these off, then that’s probably the area where I would focus on most next.