THE SPREAD OF VIRUSES TO SUSCEPTIBLE HOSTS

DURING January, February, and March, 1951, an outbreak of severe encephalitis occurred in Australia. It was confined almost completely to the region drained by the Murray River and its tributaries and for that reason was soon designated Murray Valley encephalitis. In its clinical aspects it was very similar to "Australian X disease," which was described as occurring in a wider area including the Murray Valley in 1917 and 1918 but which disappeared thereafter except for a few sporadic cases in 1922 and 1925.¹ Intensive efforts by private practitioners, public health investigators, and veterinarians during the past year have established the fact that a specific virus is the cause of Murray Valley encephalitis.² In addition to finding antibodies in significantly high titers in about 25 per cent of the population in the endemic areas, antibodies have been found in horses and a variety of wild and domesticated fowl in