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.