Some Parasites Are Worming Their Way Into a Welcome
My parents didn’t believe in giving their children much candy or snack food ... but who can stop a kid? I gleaned far and wide--even picking pre-chewed gum from the filthy playground floor.
“It was probably a good thing for you,” jokes Donald Harn, professor in the department of immunology and infectious diseases at Harvard School of Public Health. Had my squalid behavior led to an encounter with a parasitic worm (as my sister darkly threatened that it would), so much the better for me.
Harn isn’t suggesting that kids do as I did, since there can be bad germs lurking in dirt and other kids’ saliva. But he and a respectable number of other scientists think that dirt exposure in general and worm infestations in particular aren’t half as bad as they’re made out to be. Yes, worms are gross, and some are certainly harmful (causing bilharzia, elephantiasis, anemia and more). But others are fairly benign.
And worms, say the scientists, have a positive, nurturing side.
They’ve certainly been a fact of life for most human beings in the past. Infestations with worms (by which we mean primitive “helminths” such as hookworms, pinworms, tapeworms and whipworms) used to be common in the U.S. They remain so in less-developed parts of the world where sanitation is poor, parents are more relaxed about their kids playing in dirt where they can pick up helminth eggs and people don’t scrub and sterilize their environments with quite such vim and vigor as we do.
But here’s the odd thing: As we killed off the worms, the rates of certain ailments started to rise.
Allergies like asthma, for instance, are much more common in industrialized societies than primitive ones, are more common in cities than the countryside--and are on the rise in the U.S.
Autoimmune diseases of various stripes are also increasing in the Western world. Inflammatory bowel disease, for example, is a rarity in less-developed countries and was unheard of in this country until the early 1930s, says Dr. Joel Weinstock, director of the center for digestive diseases at the University of Iowa. “Whenever you see industrialization and improved lifestyle, you see a rise,” he says.
Linking immune disorders to a worm shortage might seem nutty. After all, many things change in parallel without being connected. But in defense of their theory, scientists point to studies like this: In the African country of Gabon, schoolkids whose urine tested positive for eggs of helminths called schistosomes were less likely to react allergically to a house dust mite allergen.
In other studies, mice with inflammatory bowel-like diseases got a lot better when infested with worms or chemicals made by the worms.
The theory makes sense, the scientists add, when you consider that we evolved in the constant presence of worms--and that worms can live a heck of a long time in our gut even though we’ve got a pretty fancy immune system.
“Some of them can live in us for 10 years!” says Maria Yazdanbakhsh, an immunoparasitologist at Leiden University Medical Center in the Netherlands. “If you’re going to live in a host for 10 years, you have to do something to allow yourself to stay around.”
What the worms do, says Yazdanbakhsh, is suppress parts of our immune system a tad. (She and Harn have even found some of the chemicals that do it.)
Now, however, the worms are no longer in us--and it’s happened so fast that there’s been no time for us to adapt to the change. As a result, our immune system doesn’t develop quite right, say the scientists. Without the presence of worms to keep it in check, parts are hyperreactive--increasing the risk for allergies, bowel inflammations and other immune-linked ailments.
If the worm theory is true, what do we do? Get worms? Many would find that hard to swallow, and Weinstock understands. “Nobody likes to think they have a worm within them,” he says. Right now Weinstock is testing worms as treatment, periodically feeding more than 100 sufferers of inflammatory bowel disease with a harmless whipworm that normally infests pigs and that hangs around in the human gut for just a short time. But Weinstock also imagines a day when short-term infestations with specially picked harmless worms might help prevent disease.
“Maybe one day we’ll be giving kids little pills with modified helminths in them, and maybe those kids will have little critters in them,” he says. “And maybe when they grow up they’ll be less prone to immunological disease.”
Another, arguably more palatable, prospect might be figuring out just which chemicals do this immune-shaping trick and using them instead.
“I would not give my kids worms to eat,” Yazdanbakhsh says. “But I would give my kids a preparation that I knew would do the job.”
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If you have an idea for a Booster Shots topic, write Rosie Mestel at the Los Angeles Times, 202 W. 1st St., Los Angeles, CA 90012 or e-mail rosie.mestel@latimes.com.
