Since the 1990s, doctors and researchers have puzzled over a distinct form of epilepsy that started popping up in clusters of kids across South Sudan, Tanzania, and Uganda. Without warning, kids between five and 15 years old would begin having seizures that cause them to repeatedly and uncontrollably tilt their head forward—as if they’re nodding. This “nodding syndrome,” as it was dubbed, progresses to devastating neurological degeneration, stunted growth, and in some cases death. There’s no cure and effective treatments can be hard to come by in these locales. Sporadic reports of similar cases date back to the 1960s, but for some unknown reason the syndrome seems to have flared in the past few decades, leading to thousands of estimated cases.
Yet, as years go by and case numbers rise, scientists still don’t know what’s behind the mysterious syndrome. Researchers have looked for ties to infections, malnutrition, environmental neurotoxins, genetic disorders, or some mix of some of those. But they’ve always come up empty-handed. The only persisting theory is that the syndrome is somehow linked to infections of a parasitic worm, called Onchocerca volvulus, which is spread through bites from black flies and causes river blindness. Nodding clusters tend to occur in places where the worms are endemic. Plus, researchers have repeatedly found that kids with the syndrome also tend to be infected with the worms.
The trouble is scientists have struggled to find conclusive evidence to support the theory. The worms don’t invade the brain or spinal fluid to spark seizures directly, researchers found. And efforts to find evidence that the infection might trigger neurological problems indirectly—such as by inciting a haywire autoimmune response that attacks the brain—have also turned up nothing. That is, until now.