Studies on Neurotropic Rift Valley Fever Virus:

The neurotropic strain of Rift Valley fever virus produces encephalitis when inoculated intracerebrally in lambs. Subcutaneous inoculation into sheep and lambs does not cause illness. Immunity against the pantropic strain follows the subcutaneous injection of neurotropic virus in sheep and lambs. Two species of monkey, Macaca mulatta, the rhesus monkey, and M. irus, the crab-eating macacque, are highly susceptible to intracerebral inoculation of neurotropic Rift Valley fever virus and die with encephalitis. With an increase in the number of mouse brain passages there is. a greater tendency for the virus, when injected intracerebrally in monkeys, to be found exclusively in nervous tissues.