Abstract

Vaccination against Bluetongue virus (BTV) is an essential tool for the control of the disease and for safe trade of live ruminants in accordance to OIE standards and EU legislation. The aim of this study was to determine the safety of a BTV1 modified-live virus (MLV) vaccine and its efficacy in protecting sheep against bluetongue infection. Moreover, in this study we performed a challenge trial with virulent strain BTV2 in vaccinated sheep in order to verify evidence of crossprotection. The administration of BTV1 MLV vaccine resulted to be safe, not causing in vaccinated animals significant clinical effects and haematological modifications, not showing any adverse effects in pregnant ewes if administered in the second half of gestation. However, titres and duration of viraemia recommend an awaiting period before shipment of vaccinated animals (60 days) to prevent the spread of the virus. Furthermore, this vaccine showed an appropriate balance between attenuation of virulence and ability to replicate in sheep. The antigenic stimulus provided by its replication elicits complete protection against challenge using a virulent homologous virus and does not cause any detectable viraemia in serologically positive vaccinated animals. In conclusion, the administration of BTV1 MLV vaccine was safe, not causing particular drawbacks and effective, stimulating an adequate protection of animals in case of infection with wild strain of homologous serotype.

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