Will hookworms relieve my asthma?

April 15, 2011

Dear Cecil:

I was recently distracted from my dust allergy woes by a Radiolab episode discussing how the noble but misunderstood hookworm might offer me some relief. Apparently the parasite has been shown to calm the immune system when certain allergens make it overenthusiastic. What's the straight dope?

Cecil replies:

Infecting yourself with hookworms to cure allergies? Why, it's the most brilliant idea since Julius Wagner-Jauregg's plan to cure tertiary syphilis, for which he was awarded the 1927 Nobel Prize. What plan was that, you ask? Simple. He'd give you malaria instead.

You think I'm joking. Oh, no. The thing was, Wagner-Jauregg's cure worked, sort of. The high fever of malaria killed the syphilis bacterium. The problem was you then had malaria, which five percent of the time would kill you. Then again, the mortality rate of tertiary syphilis — when the disease had invaded the brain — was 100 percent. So it seemed like a good deal till penicillin came along, after which the malaria cure was heard of no more.

The same fate undoubtedly awaits the hookworm cure, although calling it a cure based on what we know now overstates matters. The syndicated public radio program you heard featured interviews with two hookworm pioneers. One was David Pritchard, an immunologist at the University of Nottingham in the UK who's been on the front lines of hookworm research. The other was a guy named Jasper Lawrence, one of those people with a gift for latching onto an out-there concept and taking it over a cliff.

Long afflicted with severe asthma and allergies, Lawrence heard hookworms offered relief and promptly decided to get some, for which purpose he journeyed in 2006 to the tropical African country of Cameroon, where hookworm is endemic. Because (a) infected humans excrete worm eggs in their feces and (b) the resulting larvae typically burrow in through their host’s skin, Lawrence spent two weeks walking barefoot around village latrines and hoped for the best.

On returning to the U.S., Lawrence noticed no change till the spring day he rolled down his car window. Normally he would have been overwhelmed with allergy symptoms; instead, nothing. Petting a cat, previously perilous, likewise had no effect. Concluding he was cured, Lawrence decided he needed to bring the gift of hookworms to his fellow sufferers and began selling hookworm treatment kits online at four grand a pop, using worms he'd cultivated internally. (He says they're sanitized before they're shipped.) When the Food and Drug Administration went after him, Lawrence took it on the lam, although he can still be reached through his site. Meanwhile, he's gotten coverage from ABC News, Discover, Observer, and of course NPR.

In case you're tempted, I need to emphasize that Lawrence isn't a doctor and has no research to prove his worms work. However, and here we get back to David Pritchard, it's not out of the question that hookworms and their parasitic kin, collectively known as helminths, might offer some protection again asthma, allergies, inflammatory bowel disease, and other immune disorders. While working in the tropics in the 1980s, Pritchard observed that hookworm sufferers rarely had such problems. He became a believer in the hygiene hypothesis, which holds that we in the developed world receive much less exposure to infectious agents than our ancestors did, so our immune systems don't develop properly. As a result they overreact to harmless stimuli, giving rise among other things to what's been described as an asthma epidemic. Epidemiological studies purport to show that allergies and asthma are less prevalent in rural societies than in cities, that children with intestinal parasites have less severe allergic reactions, and so on. Pritchard became particularly interested in hookworms and at one point deliberately infected himself with them.

All very interesting, if a bit gross, but two points need to be made. First, no one has demonstrated that filling somebody with worms is going to cure his asthma or anything else. Although helminths and the hygiene hypothesis have been debated for decades, clinical research has barely begun. I could find only a few studies, each involving a few dozen participants. In one, porcine whipworms supposedly relieved ulcerative colitis; in another, hookworms failed to significantly improve asthma compared to a placebo. Second, even if worms conferred some clinical benefits, they're still, let's face it, worms — ones that can cause anemia, stunted development, and sometimes death, making this a suboptimal therapeutic method.

That’s not to say using one affliction to cure or prevent another is inherently nuts, just that there may be an intervening step or two before we arrive at a practical technique. Consider the famous example of Edward Jenner, who infected people with cowpox to prevent smallpox. What’s little remembered now is that cowpox vaccination replaced variolation, in which people were purposely inoculated with smallpox scabs in hopes they'd get a mild form of the disease to prevent a later fatal case. The technique worked — 98 percent of those variolated became immune. The drawback was that one to two percent died.

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References

Biggelaar, Anita H. J. van den et al. "Long-Term Treatment of Intestinal Helminths Increases Mite Skin-Test Reactivity in Gabonese Schoolchildren" JID 189 (2004): 892-900.

Cooper, Philip J. "Interactions between helminth parasites and allergy" Curr Opin Allergy Clin Immunol. 9.1 (2009): 29–37.

Dagoye, Damtew et al. "Wheezing, Allergy, and Parasite Infection in Children in Urban and Rural Ethiopia" American Journal of Respiratory and Critical Care Medicine 167 (2003): 1369-1373.

Deary, J.R. et al. "Experimental hookworm infection: a randomized placebo-controlled trial in asthma" Clinical & Experimental Allergy 40 (2009): 299–306.

Falcone, Franco H. and Pritchard, David I. "Parasite role reversal: worms on trial" Trends in Parasitology 21.4 (2005): 157-160.

Flohr, Carsten. Helminths and Allergic Disease in Vietnam Dissertation. University of Nottingham, England, September, 2007.

Grove, David I. "What is the relationship between Asthma and Worms?" Allergy 37 (1982): 139-148.

Reddy, Aditya and Fried, Bernard "An update on the use of helminths to treat Crohn’s and other autoimmunune diseases" Parasitol. Res. 104 (2009): 217-221.

Smits, Hermelijn H. et al. "Chronic Helminth Infections Protect Against Allergic Diseases by Active Regulatory Processes" Curr Allergy Asthma Rep 10 (2010): 3–12.

Turton, J.A. "IgE, Parasites, and Allergy" Lancet 308.7987 (1976): 626.

Wordemann, Meike et al. "Association of atopy, asthma, allergic rhinoconjunctivitis, atopic dermatitis and intestinal helminth infections in Cuban children" Tropical Medicine and International Health 13.2 (2008): 180-186.

Yazdanbakhsh, Maria et al. "Allergy, Parasites, and the Hygiene Hypothesis" Science 296 (2002): 490-494.

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