Abstract
Of the outbreaks of severe human encephalitis which have been recorded in Australia, five conformed to one clinical and epidemiological type. The disease was designated Australian X disease in 1917, 1918, 1922 and 1925 and Murray Valley encephalitis (MVE) in 1951. The causal virus was transmitted to laboratory animals during 1917, 1918 and 1925, but was not retained for later comparison with other viruses. The virus was isolated again during 1951 and identified as a new member of the arthropod-borne encephalitides, closely related to, but distinct from, Japanese B encephalitis virus.