What is this article about?
The Murray Valley encephalitis virus was first isolated in an epidemic in 1951. Earlier epidemics in 1917 (114 cases), 1918 (67 cases) and 1925 (10 cases) were probably also due to the virus. In 1974, the only Australia-wide outbreak occurred, involving 58 cases of encephalitis and resulting in about 20% of cases dying. Since then, there have been very few cases. The virus is endemic in Northern Australia (northern Western Australia and the top of the Northern Territory), but rarely affects humans. The occasional spread to the southern states occurs during times of heavy rainfall during the summer monsoon season via seasonal flooding of the Murray-Darling river system.