20. The encephalitis lethargica pandemic, 1915-1926
Encephalitis lethargica is also known as “sleeping sickness”, though not the same illness as that transmitted by the tse-tse fly. The disease renders its victims motionless, speechless, and inert, though fully conscious and aware of their surroundings and condition. Some victims never fully recover from the disease, remaining aware but indifferent after the acute stage of the disease passed. Others recover only to exhibit forms of psychosis not present before the disease. Recurrent tics and symptoms of Parkinson’s disease, including tremors and hallucinations, were reported among some survivors of encephalitis lethargica.
Beginning in 1915 and for the decade which followed, approximately 5 million people around the world were stricken with encephalitis lethargica. About a third of the victims died during the disease’s acute stages. In recent years, some have postulated that Adolf Hitler had encephalitis lethargica in his youth, leading to his Parkinson tremors later in his life. Scientists and doctors have yet to identify the cause of the disease. Since 1926, isolated cases have occurred, but there was no recurrence of the worldwide outbreak of the disease such as occurred during and following the First World War. The pandemic was considered a medical mystery, a description that it retains in the 21st century.