Foetal cross-protection experiments between type 1 and type 2 bovine viraldiarrhoea virus in pregnant ewes

A flock of 82 non-pregnant ewes was split into three immunisation groups an d given an intranasal dose of either cell culture medium, or a type 1 or a type 2 bovine viral diarrhoea virus (BVDV-1 or BVDV-2). Two months later th e flock was reconstituted and after a further three weeks, the ewes were br ed to pestivirus negative rams after synchronisation of oestrus using proge sterone sponges. Fifty-five ewes were segregated into three challenge group s, each of which comprised ewes from different immunisation groups. At 7 we eks gestation, one challenge group was given an intranasal dose of cell cul ture medium, whilst the other two were given intranasal doses of either BVD V-1 or BVDV-2, using the same inocula as for the immunisations. Three weeks later, the ewes were killed and their foetuses tested for the presence of BVDV-1 and BVDV-2. The results showed that immunisation of six ewes without subsequent challenge did not lead to infection of any of their 11 foetuses . Challenge with BVDV-1 or BVDV-2 in the absence of immunisation lead to 15 out of 15 or 11 out of 14 foetuses becoming infected, respectively. Immuni sation with the homologous virus to that used for challenge resulted in com plete protection of 32 foetuses from 15 ewes. Heterologous protection was o ne way. All 12 foetuses from ewes immunised with BVDV-1 were protected from challenge with BVDV-2, whereas 18 foetuses from ewes immunised with BVDV-2 were all infected after challenge with BVDV-1. This provides evidence that a recent exposure to infection with one pestivirus does not necessarily in duce foetal protection against another. The one-way result suggests that fa ctors other than antigenic differences are involved in cross-protection. Cr own Copyright (C) 1999 Published by Elsevier Science B.V.