Do Viruses Cause Parkinson Disease?

Viruses have been suspected as a cause of PD since an epidemic of “sleeping sickness” (also called encephalitis lethargica or von Economo’s encephali-tis) occurred early in the 20th century. The following description of the epidemic and the Parkinsonism that followed it (post-encephalitic Parkinsonism) is found in Oliver Sack’s book  Awakenings (Harper Collins Books).

In the winter of 1916–1917 in Vienna and other cities, a “new” illness suddenly appeared, and rapidly spread over the next three years to become world-wide in its distribution. Manifestations of the sleeping sickness were so varied that no two patients ever presented exactly the same picture, and so strange as to call forth from physicians such diagnoses as epidemic delirium, epidemic schizophrenia, atypical poliomyelitis, etc.

It seemed, at first, that a thousand new diseases had suddenly broken loose, and it was only through the pro-found clinical acumen of Constantin von Economo, allied with his pathological studies on the brains of patients who had died, and his demonstration that these, besides showing a unique pattern of damage, contained a virus which could transmit the disease to monkeys, that the identity of this protean disease was established.

In the ten years that it raged, this pandemic took or rav-aged the lives of nearly five million people before it disappeared in 1927. A third of those affected died in the acute stages of the sleeping sickness; in states of coma so deep as to preclude arousal or in states of sleeplessness so intense as to preclude sedation.

Patients who suffered but survived an extremely severe somnolent-insomniac attack of this kind often failed to recover their original aliveness. They would be conscious and aware, yet not fully awake, they would sit motionless and speechless all day in their chairs, totally lacking energy, impetus, initiative, motive, appetite, affect or desire.

They registered what went on about them without active attention and with profound indifference. They neither conveyed nor felt the feeling of life. They were as insubstantial as ghosts and as passive as zombies.

Von Economo compared them to extinct volcanoes. Although no virus comparable to that of 1917–1927 has emerged, some experts believe PD could be related to a virus, one that invades the brain and changes the genetic composition of the affected neurons. Uncommon viruses, such as Japanese B, eastern and western equine encephalitis, and St. Louis encephalitis have been linked to PD.

In addition, such common viruses as the influenza virus and possibly the West Nile virus could be linked to PD. The appeal of a viral cause of PD is that it would assume the virus, like the virus that caused von Economo’s encephalitis, invaded the brain, caused symptoms, and after a long latent period— years after the initial symptoms had subsided or disappeared—was responsible for the appearance of PD symptoms. Similar to the theoretical viral model of PD is the actual model of post-polio syndrome, which this author has developed.