Since the recent epidemic of influenza, lethargic encephalitis has appeared in this country and abroad in what is considered an epidemic form. Sporadic cases are frequently seen. Much experimental work on the cause of this disease has been done, but up to the present time, practically nothing has been established. It is significant, I believe, that the pathologic changes are chiefly about and within the small blood vessels and capillaries. Congestion and engorgement occur first, and cloudy swelling of the nerve cells appears only secondarily; later, cytolysis may occur. It is evident that the virus, whatever it be, enters the brain by way of the blood stream. This is not in harmony with the usual conception of intracranial infections, excluding the granulomas.
While encephalitis is thought to be an acute, infectious, epidemic disease, certain facts argue strongly against this: First, the unusually long prodromal stage. While an acute onset is
SALZMAN SR. IS ENCEPHALITIS AN INFECTIOUS, EPIDEMIC DISEASE?. Arch NeurPsych. 1925;14(5):638-648. doi:10.1001/archneurpsyc.1925.02200170061003