When Vik was in his late 20s, blood started appearing in his stool. He found himself rushing to the bathroom as many as nine times a day, and he quit his job at a software company. He received a diagnosis of severe ulcerative colitis, an inflammatory condition of the colon. Steroids, which suppress inflammation, didn't work for him. Sulfasalazine suppositories offered only the slightest relief. A year and a half after his diagnosis, Vik's gastroenterologist warned him that because his disease was poorly controlled, he risked developing a condition called toxic megacolon: His inflamed intestines might rupture, leading to blood infection, septic shock or death.
The doctor recommended infusions of cyclosporine, a powerful immune-suppressant drug. Vik looked it up and learned that the drug, often given to transplant recipients, in rare instances can increase the risk of fatal infection and certain cancers. And if cyclosporine didn't work, the next intervention would probably be the surgical removal of his colon. Vik might have to wear a colostomy bag for the rest of his life.
"I had a feeling there had to be a better way," he told me recently. (Worried about being stigmatized, Vik asked that I identify him only by his first name.) He began researching ulcerative colitis and discovered that the prevalence of inflammatory bowel disease — an umbrella term that includes both ulcerative colitis and Crohn's disease — had increased markedly in the United States over the 20th century. Yet the disease was less common in the developing world. He learned that exposure to dirt and unsanitary conditions early in life seemed to protect against these and other inflammatory diseases later. And then he encountered an explanation for the correlations in the research of a scientist named Joel Weinstock.
Weinstock, a gastroenterologist now at Tufts University, thought that parasites were to blame. But it wasn't their presence in the human digestive system that was causing the rise; it was their absence. To survive for years in another animal, parasitic worms, known as helminths, counter their hosts' defenses. Because an out-of-control immune response against native bacteria was thought to drive inflammatory bowel disease, Weinstock's insight was that parasites' ability to disarm the immune system might prevent the disorder. The broader implication was that the disappearance of parasites — largely eradicated from American life in the early 20th century through improvements in sanitation — might have left our immune systems unbalanced, increasing our vulnerability to all types of inflammatory disorders.