In the early 1990s, Joel Weinstock, a gastroenterologist, encountered a puzzle. The prevalence of inflammatory bowel disease (I.B.D.) across North America increased markedly during the 20th century. Many thought that “bad” genes would eventually explain the spike, but Weinstock didn’t buy it. In areas where fewer than two generations ago the I.B.D. incidence might have been as low as 1 in 10,000, it... --snip-- If eliminating worms led to an increase in disease, could re-introducing worms actually treat these diseases? In mice, the answer was yes. Worms were used to “inoculate” against mouse asthma, Type 1 diabetes, multiple sclerosis and...