Temperature dependence of the extrinsic incubation period of orbiviruses in Culicoides biting midges.
Authors: Carpenter Simon, Wilson Anthony, Barber James, Veronesi Eva, Mellor Philip, Venter Gert, Gubbins Simon
Journal: PloS one
Summary
# Editorial Summary Understanding how temperature influences viral replication within *Culicoides* midges is fundamental to predicting when and where orbivirus outbreaks occur in temperate regions—knowledge directly applicable to movement control policies and risk assessment for conditions such as African horse sickness, bluetongue and epizootic haemorrhagic disease. Carpenter and colleagues developed a novel statistical approach to estimate the extrinsic incubation period (the time viruses take to replicate sufficiently for transmission) across temperature ranges, applying this methodology to published data and new laboratory findings from three major orbiviruses in multiple *Culicoides* species. Across these different virus-vector combinations, the replication rate remained remarkably consistent at approximately 0.017–0.021 per degree-day, with a thermal threshold of 11–13°C required for virus development—notably higher estimates than previous studies had reported. These corrected thresholds and replication rates substantially improve the accuracy of transmission models, enabling more evidence-based decisions about seasonal movement relaxations and outbreak forecasting. The methodology's generic applicability to other arbovirus-vector systems offers significant practical value for the equine industry, particularly in risk zones where climate conditions and *Culicoides* activity patterns directly influence disease seasonality.
Read the full abstract on PubMed
Practical Takeaways
- •Environmental temperature directly controls transmission risk for AHSV, BTV, and EHDV; transmission becomes possible above 11–13°C and increases predictably with each degree-day, allowing better prediction of seasonal outbreaks.
- •Movement restrictions can be relaxed in temperate regions during winter months (below threshold temperatures) with greater confidence, supporting more evidence-based biosecurity policies.
- •Not all Culicoides species are equally competent vectors for the same virus; regional vector ecology must be considered alongside temperature when assessing disease risk.
Key Findings
- •Virus replication rate across orbiviruses and Culicoides vectors is approximately 0.017–0.021 per degree-day, showing consistency across different virus–vector combinations.
- •Minimum temperature threshold for orbivirus replication in Culicoides is 11–13°C across AHSV, BTV, and EHDV.
- •Previous studies underestimated replication rates and threshold temperatures due to statistical methods that incorrectly assumed all negative vectors were infected.
- •Vector competence varies significantly between different orbivirus–vector species combinations, indicating differential susceptibility independent of temperature effects.