Experimental infection and protection of lambs with a minute plaque variant of Rift Valley fever virus.

The injection of a single dose containing 5 X 10(3) plaque forming units (PFU) of a minute plaque variant of Rift Valley fever virus (RVFV) into two susceptible lambs resulted in no detectable viremia, pyrexia or clinical signs of disease. Immunization with the minute plaque variant induced neutralizing antibody as early as seven days postinoculation; however, no complement fixing antibodies were detected. Lambs immunized in this manner were protected when challenged with an infectious dose containing 1 X 10(3) PFU of wild type RVFV. These data indicate that the minute plaque variant may hold promise as a candidate live virus animal vaccine.