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.The research was done as part of a masters dissertation by
J.M. (Onderstepoort Biological Products). The practical work
was done by J.M. (Onderstepoort Biological Products) and
supervised by E.V. (University of Pretoria). E.V. (University
of Pretoria) wrote and submitted the manuscript.Onderstepoort Biological Productshttp://www.jsava.co.zahttp://upetd.up.ac.za/thesis/available/etd-07312009-145842/ab201