The Immunity Induced in Cattle and Sheep by Inoculation of Neurotropic or Pantropic Rift Valley Fever Viruses

Abstract

Cattle vaccinated with either Smithburn’s neurotropic strain, or the IBS strain of Rift Valley fever (RVF) vims had only a low-level serum neutralizing antibody response, but still possessed some degree of immunity when challenged with pantropic virus 28 months after vaccination. Some of the calves born to vaccinated pregnant cows had demonstrable antibodies in their sera before sucking colostrum. Others had no neutralizing antibody at birth, but antibody appeared in their sera after ingestion of colostrum. Two different levels of antibody response occurred in sheep after vaccination. The high-level response was associated with the presence of viraemia. High level neutralizing antibody persisted in the sera of cattle infected with pantropic virus for 2½ years and in the sera of sheep infected with pantropic virus for 3 years, these being the longest times tested.