Lambs born to ewes that had received a booster shot of inactivated bluetongue virus type 8 vaccine in the second year of a vaccination programme were protected against the disease for at least 14 weeks
Dr Chris Oura and colleagues at the Institute for Animal Health (IAH) have shown for first time that lambs born to ewes that had been vaccinated in the second year of a vaccination programme with inactivated bluetongue (BT) virus type 8 vaccine (the second shot being a booster one month before lambing) were protected against disease for at least 14 weeks, the age at which many lambs go for slaughter.
The protection was a result of high amounts of colostral antibody passed from ewe to offspring. This research, which was supported by Defra and done in collaboration with Professor James Wood at the University of Cambridge and the Veterinary Laboratories Agency Weybridge, has just been published in the journal Vaccine*. IAH is an institute of the Biotechnology and Biological Sciences Research Council (BBSRC).
Lower amounts of colostral antibody were transferred to lambs from ewes in the first year of a vaccination programme in which the ewes had only been vaccinated once. Although these lambs were not challenged with BT virus in the experiment, the low amounts of antibody passed to the lambs suggested that lambs born from single vaccinated sheep were likely to be protected for a shorter time than lambs born from ewes that were in the second year of a vaccination programme and had been vaccinated in both the first and the second year.
"The experiment was designed in response to wishes expressed to me by farmers,"
said Dr Oura, "who wanted to know how long lambs born from vaccinated ewes were protected for. Many farmers also expressed a wish to vaccinate their ewes with inactivated BT vaccine at the same time as combined clostridial/pasteurella vaccine so they could avoid having to vaccinate their pregnant ewes on two occasions with different vaccines shortly before lambing."
The sheep used had been first vaccinated with BTV-8 vaccine on a farm in East Anglia in May 2008. The booster BTV-8 vaccine was given at the same time as clostridial/pasteurella vaccine, in November 2008, approximately four weeks before lambing.
In a related study published in December**, Oura and colleagues showed that sheep vaccinated once with inactivated BTV-8 vaccine on a farm in East Anglia had protection for at least 10 months, more than sufficient for the UK midge season.
Bluetongue virus first came to the UK in August 2007, brought by BT virus serotype 8-infected Culicoides biting midges from the near Continent, where it had arrived in 2006. Inactivated BT virus type 8 vaccine became available in the UK from May 2008. Voluntary vaccination contributed to there being no cases of bluetongue in the UK in 2008, despite tens of thousands of cases of the disease on the Continent. There were no cases of the disease in Britain last year.
