Schmallenberg virus: State of Art
This scientific report provides an overview of all research carried out on Schmallenberg virus (SBV), reviewing the current knowledge on SBV regarding genotyping findings, susceptible species, pathogenesis, transmission routes, immunity, seroprevalence, geographical and temporal SBV spread, improved within-herd transmission model, SBV impact assessment and within-herd and regional spread models. Metagenomic analysis identified SBV as a novel orthobunyavirus emerged in 2011 and it has been detected in domestic cattle, sheep, goats and 12 wild species. Seroprevalence studies indicate that SBV has probably spread over the whole of Europe, showing high seroprevalence at national scale, while larger variability is observed at regional scales. Clinical disease frequency is low and experimental infection on pregnant ewes and cows suggest that SBV rarely induces malformations. SBV may be detected from semen with a low frequency though there is no scientific evidence of transmission through insemination. Vector competence studies suggest that Culicoides are likely to be able to transmit SBV but found no evidence that mosquitoes are likely to be able to transmit it. SBV vertical transmission has not yet been identified as a major route. SBV has successfully overwintered, despite lengthy period of minimal vector activity and duration of immunity in cattle lasts for at least one year. A farm-to-farm spread model for SBV shows a rapid spread of infection across the study region and latent period, duration of viraemia, probability of transmission from host to vector and virus replication are sufficient to account for the rapid SBV spread. The between-farm SBV transmission model indicates that the application of movement restrictions has little effect on SBV spread. An impact assessment based on limited data suggests a probable effect of SBV infection on abortion, short gestation, non-return and the number of artificial inseminations required per animal. International trade restrictions by third countries represent the main SBV impact.