Why was the 1918 influenza pandemic so lethal? The possible role of a neurovirulent neuraminidase.

Epidemiological, viral, behavioral and neuropathological evidence suggests that some influenza epidemics were neurovirulent. Re-examination of the data from the lethal 1918 pandemic armed with recent observations about the influenza virus implicates a neurovirulent influenza virus in manic-depressive disease, schizophrenia and Parkinson's disease. The neurovirulence seems to have been related to the species of neuraminidase.