title: Evaluation of a formalin-inactivated Rift Valley fever vaccine in sheep.
abstract: A formalin-inactivated Rift Valley fever (RVF) vaccine prepared in cell culture for human use was immunogenic in sheep. Vaccine was administered as a single dose of diluted (1:5) or undiluted vaccine with or without an adjuvant. Serum-neutralizing antibodies induced by RVF vaccine persisted for at least 7 months. Seven of 11 vaccinated sheep with prechallenge plaque-reduction neutralization (PRN80) antibody titers of less than or equal to 10 were protected against challenge exposure with 10(6) plaque-forming units of Zagazig 501 strain of RVF virus. Challenge exposure induced abortion in 2 of 2 pregnant sheep. Five sheep with PRN80 titers greater than or equal 1:20 were protected from detectable viremia after challenge exposure. Additionally, 5 of 6 lambs (3 months old) were protected (by maternal antibodies) against challenge exposure. Challenge control sheep developed clinical disease and detectable viremia after exposure. Virus was isolated from saliva of 1 challenge control sheep and virus was transmitted by contact exposure to 1 of 4 seronegative contact-control sheep. Immunization of sheep with formalin-inactivated RVF vaccine induced a priming effect against RVF viral antigens. Challenge exposure with RVF virus resulted in significantly higher neutralizing titers in vaccinated sheep than in nonvaccinated sheep.
mesh_terms: D000818:Animals; D006224:Cricetinae; D005069:Evaluation Studies as Topic; D005260:Female; D008297:Male; D008431:Maternal-Fetal Exchange; D011247:Pregnancy; D012295:Rift Valley Fever / Q000276:immunology / Q000382:microbiology / Q000517:prevention & control*; D012296:Rift Valley fever virus / Q000302:isolation & purification; D012756:Sheep; D012757:Sheep Diseases / Q000276:immunology / Q000517:prevention & control*; D014611:Vaccination / Q000662:veterinary*; D014613:Vaccines, Attenuated / Q000276:immunology; D014765:Viral Vaccines / Q000276:immunology
chemical_list: D014613:Vaccines, Attenuated; D014765:Viral Vaccines