Author(s): Smithburn JS, Hughes TP, Burke AW, Paul JH
A virus, named by the authors "West Nile Virus" was isolated from the blood of a febrile native of Uganda by the inoculation of the serum intracerebrally into mice. It was easily propagated by serial passage through the brains of mice and, after the first mouse passage, was uniformly fatal. It passed readily through Berkefeld V. N. and W candles and Seitz EK asbestos pads; its size, estimated by filtrations through graded collodion membranes, was found to be 21-31 mm. The virus is pathogenic for mice by intra.cerebral, intranasal or intraperitoneal inoculation but not when given subcutaneously. Rhesus monkeys are also susceptible; either intracerebral or intranasal inoculation of the virus results in an encephalitis which may prove fatal. The African monkey, Cercopithecus, ethiops centralis, and rabbits, guineapigs and hedgehogs, are not susceptible though they can be "immunized" to yield virus neutralizing serum antibodies. The specific antibodies in immune sera may be demonstrated by virus neutralization tests in mice, using either the intracerebral or intraperitoneal routes of inoculation. These antibodies were not present in the woman from whom the virus was isolated, at the time of the isolation, but developed in her serum some time later. They developed also in two persons who were working intensively with the virus, although these showed no clinical signs of infection, and they were present in one out of five sera taken from individuals residing in the West Nile district. By virus neutralization tests in mice it was shown that there is an immunological relationship between West Nile Virus and the virus of Japanese B encephalitis. Histological study indicated that the new virus is strictly neurotropic but produces lesions of the central nervous system which are quite different from those produced by the other known neurotropic viruses.