ABSTRACT
Between 1917 and 1925, outbreaks of severe encephalitis occurred in Queensland, New South Wales, and Victoria in eastern Australia. The previously undescribed disease, originally termed Australian X disease, had a high-fatality rate, and children under the age of 15 were most affected. Australian X disease is now known to be caused by the mosquito-borne virus Murray Valley encephalitis virus (Flaviviridae: Flavivirus; MVEV), although retrospectively it is now recognized that some of the earlier encephalitic cases may have been caused by the closely related West Nile (subtype Kunjin) virus (Flaviviridae: Flavivirus; KUNV) that also occurs in Australia [1]. Murray Valley encephalitis virus is now known to be enzootic in parts of northern Western Australia, the Northern Territory, and possibly northern Queensland, and epizootic in more southerly regions of Western Australia, the Northern Territory, Queensland and the southeastern states of New South Wales, Victoria, and South Australia [2]. Figure 19.1 shows the pattern of epidemic activity of MVEV in Australia. It has also been known to occur in Papua New Guinea [1,3].
