Twelve years ago, my husband and I packed up all of our belongings and moved to Trivandrum — a steamy, tropical town at the southern tip of India in Kerala. At the time, I was a medical student interested in studying stroke. For the next six months I dressed in a sari and walked to work on jungle roads. At the hospital, I immediately began seeing a steady stream of young patients affected by strokes, many of whom were so severely disabled that they were unable to work. I initially suspected the cause was tuberculosis or dengue fever — after all, this was the developing world, where infections have long been primary culprits for disease. But I soon learned that my hunch was wrong.