Dose-dependent effect of experimental Schmallenberg virus infection in sheep

Schmallenberg virus (SBV) is an orthobunyavirus affecting European domestic ruminants. In this study, the dose-dependent effect of experimental infection of sheep with SBV was evaluated. Four groups of three ewes were each inoculated subcutaneously with 1 mL of successive 10-fold dilutions of an SBV infectious serum. The ewes were monitored for 10 days, but no clinical signs were observed. The number of productively infected animals within each group, as evidenced by viraemia, seroconversion and viral RNA in the organs, depended on the inoculated dose, indicating that a critical dose has to be administered to obtain a homogeneous response in infected animals under experimental conditions. In the productively infected animals, no statistical differences between the different inoculation doses were found in the duration or quantity of viral RNA circulating in blood, nor in the amount of viral RNA present in virus positive lymphoid organs.