The closer scientists look at the epidemiology of [tapeworms in the brain, neurocysticercosis], the worse it becomes. Nash and other neurocysticercosis experts have been traveling through Latin America with CT scanners and blood tests to survey populations. In one study in Peru, researchers found 37 percent of people showed signs of having been infected at some point. Earlier this spring, Nash and colleagues published a review of the scientific literature and concluded that somewhere between 11 million and 29 million people have neurocysticercosis in Latin America alone. Tapeworms are also common in other regions of the world, such as Africa and Asia. “Neurocysticercosis is a very important disease worldwide,” Nash says.