As Weinstock considered the I.B.D. puzzle, he wondered if immune manipulation by worms could incidentally protect against other diseases.

Comparison of the prevalence of I.B.D. and surveys of worm-infestation rates revealed a telling pattern. About 10 years after improved hygiene and deworming efforts reduced worms in a given population, I.B.D. rates jumped. Weinstock had his hypothesis: after a long coevolution, the human immune system came to depend on the worms for proper functioning. When cleaner conditions and new medicines evicted the worms from our bodies, the immune system went out of kilter. “Hygiene has made our lives better,” says Weinstock, now at Tufts University. “But in the process of eliminating exposure to the 10 or 20 things that can make us sick, we’re also eliminating exposure to things that make us well.” nullnull

Weinstock spotted a prime candidate on pig farms. Pig farmers are chronically exposed to Trichuris suis, the pig whipworm, and tolerate it with no apparent side effects. (This is not the potentially dangerous worm found in undercooked pork.)

In 2005, he published results from two human studies. After ingesting 2,500 microscopic T. suis eggs at 3-week intervals for 24 weeks, 23 of 29 Crohn’s patients responded positively. (Crohn’s disease belongs to the I.B.D. family, which also includes ulcerative colitis.) Twenty-one went into complete remission. In the second study, 13 of 30 ulcerative colitis patients improved compared with 4 in the 24-person placebo group.

As Weinstock considered the I.B.D. puzzle, he wondered if immune manipulation by worms could incidentally protect against other diseases.

Comparison of the prevalence of I.B.D. and surveys of worm-infestation rates revealed a telling pattern. About 10 years after improved hygiene and deworming efforts reduced worms in a given population, I.B.D. rates jumped. Weinstock had his hypothesis: after a long coevolution, the human immune system came to depend on the worms for proper functioning. When cleaner conditions and new medicines evicted the worms from our bodies, the immune system went out of kilter. “Hygiene has made our lives better,” says Weinstock, now at Tufts University. “But in the process of eliminating exposure to the 10 or 20 things that can make us sick, we’re also eliminating exposure to things that make us well.” nullnull

Weinstock spotted a prime candidate on pig farms. Pig farmers are chronically exposed to Trichuris suis, the pig whipworm, and tolerate it with no apparent side effects. (This is not the potentially dangerous worm found in undercooked pork.)

In 2005, he published results from two human studies. After ingesting 2,500 microscopic T. suis eggs at 3-week intervals for 24 weeks, 23 of 29 Crohn’s patients responded positively. (Crohn’s disease belongs to the I.B.D. family, which also includes ulcerative colitis.) Twenty-one went into complete remission. In the second study, 13 of 30 ulcerative colitis patients improved compared with 4 in the 24-person placebo group.<