Human cases of the disease have been reported since the late 1970's.
Death rates are much higher for infected animals.
RVFV is transmitted to humans primarily by infected Aedes or Culex mosquitoes and by direct contact with the blood or body fluids of infected animals. Vaccines for veterinary use are available, but are known to cause birth defects and abortions in sheep and provide only low-level protection in cattle. No effective vaccine or antiviral medication is approved for use in humans. Unfortunately, it also gives rise to significant pathogenic side effects in cattle. A distinct, naturally-derived variant, Clone 13, includes an attenuation in the S segment and expresses good immunogenicity.