Colostral antibody protection and interference with immunity in lambs born from sheep vaccinated with an inactivated Bluetongue serotype 8 vaccine.

Widespread vaccination programmes against Bluetongue virus serotype 8 (BTV-8), using inactivated vaccines, are being carried out across many countries in northern, western and southern Europe. This study investigates the extent and length of colostral antibody protection, as well as the degree of colostral antibody induced interference of the immune response to BTV-8, in sheep. Significantly lower titres of neutralising antibodies were transferred in colostrum to lambs born from sheep vaccinated once as opposed those vaccinated twice (single vaccine in the first year and a booster vaccine in the second year). On BTV-8 challenge, lambs born from sheep vaccinated on two occasions, with the second booster vaccine given approximately 1 month prior to lambing, were protected from clinical disease for up to 14 weeks. BTV-8 was isolated from 5 of the 22 challenged lambs, although only one of these lambs showed a transient rise in body temperature with no other clinical signs. Lambs born from ewes given a second booster vaccine 1 month prior to lambing, are likely to be protected from clinical disease for at least 14 weeks, whereas lambs born from ewes vaccinated once are likely to be protected for a shorter time. Colostral antibodies present in the 13-14-week-old lambs appeared to interfere with the humoral response to challenge virus. These results suggest that colostral antibodies may interfere with vaccination in lambs up to at least 14 weeks of age.