Regarding Asthma and Parasites

What if the asthma epidemic in the Western world started because some people’s immune systems freak out in the absence of former health threats?

That’s the reasoning behind the Hygiene Hypothesis, and it also explains why some people inflict parasitic infections on themselves in an attempt to reduce their allergy and asthma symptoms.


A reader asked me about this story a month ago. I’d already been glancing at parasite articles with my brain half-engaged, and her email prompted me to actually sit down and do some more focused reading. Here’s what I found:

Back in 2004, Yale scientists discovered high levels of chitinase in asthma patieints’ lung tissue. Chitinase is an immune system enzyme that breaks down chitin, the exoskeleton material of insects and parasites. Now, considering the researchers couldn’t detect any chitinase in non-asthmatics’ lung tissue, well, you can see where this is heading.

– Next up, a 2006 meta-analysis of epidemiological research on the possible protective factor of intestitnal parasites against asthma. In a meta-analysis, scientists examine previous studies on a specific subject altogether, as a body of research. Here’s the key passage:

An alternative explanation is that the associations we have observed arise from reverse causation, and that, in particular, allergic individuals are less likely to acquire hookworm infection. The cross-sectional nature of the data available to us precludes any further insight into this possibility. Overall, however, our study indicates that different species of parasite infection may have important effects on the pathogenesis of asthma, and that in particular, the potential individual or public health benefits of hookworm infection merit further investigation. [emphasis mine]

In March of this year, the University of Pennsylvania identified an immune system cell population that appears to fight parasites and in the developed, sanitized world, possibly leads to the asthma and allergy response.

Finally, here’s a pretty good overview of the people who’ve taken this research and run with it. And by “run with it,” I mean “infected themselves with parasites on purpose.” A couple of companies are making money off the phenomenon, too.

That’s a lot of information to take in, so here’s the Asthma Mom distillation:

1. Humans have immune systems that used to fight off parasites all the time, for pretty much most of our history.
2. Modern medicine figured out how to prevent and treat parasitic infections. That’s a good thing; parasites can do some nasty damage.
3. With the parasites gone, some people’s immune systems go off the rails.
4. They’re poised to fight, but the target’s gone.
5. So they turn and attack within. In the case of asthma, that means the airways.
6. Some patients say, okay. If my immune system wants parasites, I’LL GIVE IT SOME PARASITES.
7. And they do, hoping to keep their immune systems too busy fighting those off to go into bronchospasm.

They’re trading the old problem for the newer one, basically, without FDA regulation, extensive human clinical trials, or the knowledge of any long-term health effects.

On the other hand, scientists are researching the parasite/asthma link – and the many variables associated with it – further, and we could actually see a safe, medically approved treatment based on this very theory someday:

Doctors and researchers say the worm therapy idea not only holds water, it is a promising wide-reaching treatment with FDA-monitored clinical trials for patients in several major U.S. cities. Source

Photo: Fluorescence microscope image from Wikimedia Commons user Roberto Dabdoub.

71 responses to “Regarding Asthma and Parasites”

  1. Elisheva says:

    I actually am a huge fan of the hygiene hypothesis. Asthma is way higher in the western world than it is elsewhere. And it’s gotta be from this. And I’m gonna let my future kids wallow in the mud as much as they want and eat off the floor. Well, to a degree anyway. That said, I used to eat the dirt out of potted plants and suck on my mom’s shoes (she’s a vet. how gross is that?) when i was a toddler and that didn’t seem to do me much good in terms of my lungs staying good.

  2. Sara C. says:

    great picture choice.

    I also agree with the hygiene theory. However, once my kid became “chronically ill” I became a bit of a germ freak….I really never was before. We never used hand sanitizer, I followed the “5 or 10 second rule” I might blow on something after I picked it up off the floor, and gave it to them to eat.

    THEN…you get a kid who gets a cold and ends up in the ER…and, well, I got a little fanatical about germs. (having a friend with a kid with CF doesn’t help, either)

    BUT, all that said…I think agree that things are on the rise because we are far too clean. Our bodies don’t have to fight what they need to, so they fight themselves. There is a huge uprise in tons of autoimmune diseases…not just in asthma and allergies.

    Very interesting.

  3. Amy says:

    Right, but it’s important to remember, too, that if the hygiene hypothesis plays a role, it’s only part of a whole complex group of other components and risk factors.

    Everyone in my family grew up in the developed world, for example, yet only my older daughter has asthma. And as Elisheva mentioned, I didn’t freak out about either of my girls playing on the ground as babies or getting dirty, and I don’t use antibacterial hand soap or dish soap, etc. in my house. I don’t even use bleach, except during stomach bugs and last fall’s H1N1 outbreak, yet my older daughter has asthma.

    I grew up in a family of 6, and none of us has it, either. No one in Mr. Asthma Mom’s family has asthma. Point is, AG was predisposed already, developed/sanitized society or not.

    And certainly I won’t want to go back to pre-penicillin, pre-parasite treatment days. It’s like the air pollution/car dilemma – it’d be nice if we could all get rid of our cars and clean the air up, but that’s just not feasible.

    Mostly though, i think countries like the U.S. DO need to stop using things like industrial-strength and/or synthetic cleaners and antibacterial soap for every little thing (except in hospitals, obviously), and particularly not for daily household use. Not just because of the hygiene hypothesis, but also because of the danger of creating superbugs.

    And clearly, I’m not going to buy parasites online to treat my daughter’s asthma, lol.

  4. Kelley says:

    Just another thought (since I’m so odd)… my AG’s asthma was triggered by a sinus infection, which came on shortly after her starting daycare… my sister had watched her prior to then with her own 2 daughters… my AG’s adenoids went absolutely NUTS. The sudden barrage of germs from being in such close contact to other kids sent her whole immune system haywire and in overtime. It did not know what to do at all. I do not know, and probably never will, whether her asthma would not have been “triggered” if my sister had continued watching her at home, or if it just would have been later…? There are just SO MANY variables with this! Also, on a side note, I do have a family history of autoimmune diseases (Lupus, Sjogrens).

  5. Allison says:

    Thanks for the post Amy, it was great. There was a recent episode on This American Life about hookworms and asthma (read more here: After it aired, several people at work asked me if I was going to give my son hookworms. I live in alt-med central up here in VT, where people look askance at the fact that I give my son corticosteroids and even more askance that I won’t give him non-FDA approved hookworm therapy. I think I’ll let a few more clinical studies happen first, call me crazy…

    Same scenario at our house — no antibacterial soap, no bleach, lots of kids playing in dirt, eating dirt, licking dirt! And one kid who ends up with asthma. But I think I’ll still happily stick with these odds than the olden days of plenty of parasites, but also lots of infectious disease and much higher infant mortality.

  6. KC says:

    I had ringworm and pinworms as a kid and that didn’t stop me from having severe asthma my entire life.

  7. Sara C. says:

    Amy…that’s very true. I can tell you that Mariella comes by it honestly….I’m asthmatic, my mother is asthmatic…I’m not sure if anyone else is too…so there is a genetic component.

    I don’t super clean my house…I just super clean my kids hands. (I only bleach the toilet.) Though I have been steam cleaning the floor…and that makes me feel pretty good.

    yeah, I’m not introducing any parasites either…and I use antibiotics when I am told to.

  8. Amy says:

    Kelley–What’s interesting in my house is AG started going to an in-home daycare (her and 4 other kids) when she was 6 months-old, but by the time I had her sister, I was working from home. So my kid who attended daycare ended up with asthma, but my non-daycare kid didn’t. In my case, I do think she would’ve developed asthma, anyway, but you’re right – there are SO many variables and risk factors.

    Allison–Whenever I encounter parents who talk about inhaled corticosteroids like poison, I tell them about the first time the dr. prescribed them for my kid & I, undereducated about asthma and misinformed at the time, ignored the advice, didn’t put her on a maintenance regimen, and subjected her to several long months of miserable health as a result. It’s not a story I’m proud of, but I tell it for the greater good. :) They don’t usually have much else to say when I’m done!

    KC–Thanks for sharing, though I’m sorry you have severe asthma.

    Sara–Even though none of the parents, grandparents, aunts, or uncles have asthma, two of my kid’s first cousins have it – almost like it skipped a couple generations.

  9. Sarah says:

    Thankfully that hasn’t had a lot of press time where I live!

    I live in a university town, which for some reason attracts all manner of “alternative” therapies, which I give neither confidence nor credit to. I’m okay with the ones that have passed scientific scrutiny (chiropractic for lower back pain, acupuncture for chronic pain, as two examples) but when you get into stuff that there’s no evidence for it working aside from a placebo effect (chiropractic for asthma, for example: there are some chiropractors who, though in Canada they’re not allowed to claim that they can treat asthma, will instead dance around the law by saying they treat the subluxations that “cause” asthma, that they restore the body’s natural rhythm so that breathing and other systems can return to normal, or they’ll say that asthmatics find chiropractic helps them – but the only studies that I’ve found which allegedly support this were not double-blind, didn’t use control groups and included a step-up in asthma medication so there’s no way of telling whether the improved control was due to the chiropractic treatment – which I doubt – or the increased medication), I have no support, and I go so far as to discourage people who I think are getting bilked from taking the ‘alternative’ therapy as a substitute for mainstream, proven therapy.

    As for the parasites, it does sort of make sense, and I’ve seen a few initial studies that look promising, but I think I’ll watch a few more of the clinical trials before I even consider giving myself parasites!

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