IFL Science The disease affected millions, but to this day has not been satisfactorily explained. The symptoms were pretty distressing. Around a century ago, and around the same time the 1918 influenza pandemic killed between 50 and 100 million people worldwide, humanity was met with a new and unusual disease. The disease, known as encephalitis lethargica (EL), first began to spread across Europe in the winter of 1916. Constantin von Economo, a doctor at the Psychiatric-Neurological Clinic of the University of Vienna, was the first to describe the disease after several patients showed up with strange neurological symptoms. They were admitted with diagnoses ranging from meningitis and multiple sclerosis to delirium. But none of these symptoms fit neatly into any known disease, and one new symptom – lethargy, or sleepiness – distinguished it as a new phenomenon. It was categorized as either acute or chronic, though the two phases often blended together.
“Acute encephalitis lethargica often presented as a gradual onset of non-descript flu-like symptoms, including malaise, low-grade fever, pharyngitis, shivering, headache, vertigo, and vomiting,” a 2017 review of the topic explains. “Neurological symptoms followed and could present very quickly, as in the case of a girl who experienced a sudden hemiplegia while walking home from a concert. Within half an hour she was asleep, and died 12 days later.”