Meet Your Parasites: Can They Help Heal Autoimmune Disorders?
Years after scientists first noticed that autoimmune disorders rise as our environment gets cleaner, a new generation of researchers is looking at parasites not as a scourge but as a possible cure.
One chilly November morning, I head south from San Diego in a bottom-tier rental car. As I drive, the radio announcer reviews some of the most recent drug violence in Tijuana, where I’m headed. More than this ongoing brutality, however, parasites occupy my mind—worms that migrate through flesh, burst into lungs, crawl down throats, and latch on to tender insides. Any traveler might fret over acquiring such hangers-on while abroad. But I’m heading to Mexico precisely to obtain not just one, but a colony. Today in Tijuana I’ll deliberately introduce the hookworm Necator americanus —the American murderer—into my body.
Scientists are of two minds about parasites these days. Some consider them evil incarnate, but others note that the majority of humans infected with parasites today—upward of 1.2 billion people—host worms with few apparent symptoms. This camp has begun to suspect that worms may, in fact, confer some benefits on their human hosts. That brings me to my motive: A large and growing body of science indicates that parasites may prevent allergies and autoimmune diseases. And I’ve got both.
When I was 11, my hair began falling out. A dermatologist diagnosed alopecia areata, an autoimmune disorder. My immune system, normally tasked with protecting against invaders, had inexplicably mistaken friend for foe and attacked my hair follicles. I also suffered from fairly severe asthma as a child, and food allergies to peanuts, sesame, and eggs. My alopecia advanced until, by age 16, not a single hair remained on my body.
The National Institutes of Health estimates that between 14.7 and 23.5 million Americans have an autoimmune disease, or 5 to 8 percent of the population. The American Autoimmune Related Diseases Association puts the number at more than double that—50 million Americans. In the United States, autoimmune disease ranks among the top 10 killers of women—roughly three-quarters of those afflicted with autoimmune disease are female.
These statistics apply to the richest countries in the early 21st century. But immune-mediated diseases weren’t always this prevalent. Early hints of immune dysfunction during the late 19th century notwithstanding, the allergy and asthma epidemics gained steam during the 1960s, accelerated through the 1980s, and then plateaued by the early 2000s. In that period, depending on the study and the population, you’ll find somewhere between a doubling and a tripling of asthma and allergies in the developed world.
Some autoimmune diseases show even more dramatic increases. A 2009 study found that the prevalence of undiagnosed celiac disease had increased more than fourfold since the mid-20th century. The incidence of multiple sclerosis has nearly tripled. And for some of these diseases, there’s no end in sight. The incidence of type 1 diabetes, which more than tripled during the late 20th century, is estimated to double again by 2020.
What has happened? In 2002, the French scientist Jean-François Bach published a seminal paper for anyone asking that question. The study, which appeared in The New England Journal of Medicine , had two graphs side by side, one showing the gradual decline since 1950 of once-common infectious diseases—hepatitis A, measles, mumps, and tuberculosis—next to another showing, over the same period, an increase of autoimmune and allergic disease in the developed world. Nearly everyone contracted mumps and measles in 1950. By 1980, almost no one did. Vaccines had almost eliminated both viruses. In an even shorter period—since 1970—new cases of hepatitis A infection fell to one-fifth their former level. And all the while, new cases of asthma, multiple sclerosis, and Crohn’s disease doubled, tripled, and quadrupled, respectively.
If you retrace your own lineage back a few generations, you’ll probably find hay fever and asthma lessening with each one. You (like me) may have lifelong asthma and food allergies, for example. Your parents, meanwhile, maybe had seasonal hay fever. But relatively few of your grandparents’ generation—or great-grandparents, as the case may be—suffered from sneezing or wheezing of any sort. This pattern likely relates not to new exposures, but to the removal of old ones—exposures of the sort still prevalent in many parts of the developing world.
You’ve probably heard peripherally about the many allergens, such as dust mites, peanuts, and tree pollen, which cause allergies. Maybe you’ve heard reference to the infections and toxic pollutants that provoke autoimmune disease. Without suggesting that these ideas are totally unfounded, here’s an alternative and