title: Determination of the minimum protective dose for bluetongue virus serotype 2 and 8 vaccines in sheep.
abstract: Recent outbreaks of bluetongue virus (BTV) serotypes 2 and 8 in many European countries  provided an opportunity to investigate the possibility of improving the safety of the modified  live vaccines administered mainly in South Africa. Modified live vaccines (MLV) released at  a titre of 5 x 104 PFU/mL, raised concerns and prompted the need to determine the minimum titre which will still be protective and also safe. The BTV serotypes 2 and 8 vaccines were  produced at the following titres: 102 PFU/mL, 103 PFU/mL and 104 PFU/mL, and were injected into 24 sheep which were then monitored. Blood was collected on days 0, 3, 6, 9, 12, 15, 18, 21, 25, 28 and 4 months post vaccination, for seroconversion and viraemia studies. These sheep were later challenged at 4 months post vaccination using BTV infected cell culture material, they were then observed and bled and again tested for viraemia. There was no viraemia post vaccination, however, a febrile reaction did occur and seroconversion was demonstrated at low titres for both BTV 2 and 8. Although viraemia was demonstrated post challenge, sheep vaccinated with the low titre BTV 2 vaccine showed more than a 90% protection index at a  lower titre of 103 PFU/mL, compared with BTV 8 that showed a protection index above 90%  at all the titres used. It is recommended that for BTV 2 vaccine, sheep should be vaccinated at  a titre of 103 PFU/mL and at a titre of 102 PFU/mL with BTV 8 vaccine.
authors: Onderstepoort Biological Products Ltd., Onderstepoort, South Africa.
authors: Jacob
authors: J
authors: Modumo
authors: Estelle H
authors: EH
authors: Venter
mesh_terms: D000818:Animals; D001819:Bluetongue / Q000517:prevention & control*; D001820:Bluetongue virus / Q000145:classification* / Q000276:immunology; D012703:Serotyping; D012756:Sheep; D014765:Viral Vaccines / Q000276:immunology*; D014766:Viremia
chemical_list: D014765:Viral Vaccines