Quantitative Risk Assessment for African Horse Sickness in Live Horses Exported from South Africa.
Authors: Sergeant Evan S, Grewar John D, Weyer Camilla T, Guthrie Alan J
Journal: PloS one
Summary
# African Horse Sickness Risk in Live Horse Exports: What the Numbers Tell Us African horse sickness poses a genuine biosecurity threat to importing countries receiving live horses from endemic regions like South Africa, yet quantifying this risk has been challenging until now. Sergeant and colleagues developed a stochastic model to estimate the probability of undetected AHS infection slipping through OIE-compliant pre-export quarantine procedures, incorporating variables such as disease prevalence, vector exposure risk, and diagnostic test sensitivity. Exporting from a low-risk area with standard protocols and no post-arrival quarantine carried a median risk of approximately 5–6 infected horses per million exported (annual probability of 0.0016 for typical export volumes of 300 horses yearly), whereas endemic areas presented 15–17 times higher risk under identical conditions. The addition of a single PCR test during vector-protected post-arrival quarantine reduced transmission probability by roughly 12-fold, providing a practical, evidence-based tool for risk mitigation. For veterinarians, equine authorities, and importing nations, this work offers quantitative guidance for tailoring biosecurity measures to acceptable risk thresholds, rather than applying a one-size-fits-all approach to trade restrictions.
Read the full abstract on PubMed
Practical Takeaways
- •If importing horses from South Africa or endemic AHS regions, implement vector-protected quarantine with at least one additional PCR test to substantially reduce disease risk
- •Source country matters significantly—horses from demonstrated low-risk areas carry 15-17× lower infection probability than endemic areas, making supplier location a critical risk factor
- •Risk mitigation is achievable through testing and quarantine protocols, allowing continued trade while maintaining disease security appropriate to your country's tolerance level
Key Findings
- •From low-risk areas, estimated median of 5.4 infected horses per 1 million exported without post-arrival quarantine, equating to annual probability of 0.0016 at 300 horses/year
- •Additional PCR testing during vector-protected post-arrival quarantine reduced infection probabilities by approximately 12-fold
- •Horses exported from endemic AHS areas showed 15-17 times higher infection probabilities compared to low-risk areas under comparable scenarios
- •Risk management through multiple PCR tests and vector-protected quarantine can effectively minimize probability of undetected AHS infection in exported horses