Encephalitis and encephalopathy associated with pandemic flu

Avian influenza A (H5N1) viruses in birds in parts of Asia, Africa, and Middle East continue to cause human diseases and to pose the threat of human pandemic flu. Pandemic flu is characterized by respiratory symptoms and is a cause of high fatality rates in the younger population. Previous studies have shown that avian influenza A (H5N1) viruses in humans might also target organs other than lungs. Historical records reveal that in 1918, more than 40 million people died due to influenza pandemic; this pandemic was rapidly followed by an epidemic of encephalitis lethargica in 1919. From the mid-1990's, there have been outbreaks of encephalopathy in Japan which appear to be associated with influenza. In this article, neurological complications associated with influenza have been reviewed by taking a closer look at previous influenza pandemics in the 20th century and seasonal influenza epidemics in Japan; this will enhance preparations against human pandemics. In addition, we have also reviewed a few human cases of avian influenza A (H5N1) infection where the central nervous system (CNS) are involved.