Department of Production Animal Studies, University of Pretoria, Pretoria, Gauteng, South Africa.
South African Equine Health and Protocols NPC, Cape Town, Western Cape Province, South Africa.
PLoS One. 2021 May 26;16(5):e0252117. doi: 10.1371/journal.pone.0252117. eCollection 2021.
South Africa is endemic for African horse sickness (AHS), an important health and trade-sensitive disease of equids. The country is zoned with movement control measures facilitating an AHS-free controlled area in the south-west. Our objective was to quantitatively establish the risk of entry of AHS virus into the AHS controlled area through the legal movement of horses. Outcomes were subcategorised to evaluate movement pathway, temporal, and spatial differences in risk. A 'no-control' scenario allowed for evaluation of the impact of control measures. Using 2019 movement and AHS case data, and country-wide census data, a stochastic model was developed establishing local municipality level entry risk of AHSV at monthly intervals. These were aggregated to annual probability of entry. Sensitivity analysis evaluated model variables on their impact on the conditional means of the probability of entry. The median monthly probability of entry of AHSV into the controlled area of South Africa ranged from 0.75% (June) to 5.73% (February), with the annual median probability of entry estimated at 20.21% (95% CI: 15.89%-28.89%). The annual risk of AHSV entry compared well with the annual probability of introduction of AHS into the controlled area, which is ~10% based on the last 20 years of outbreak data. Direct non-quarantine movements made up most movements and accounted for most of the risk of entry. Spatial analysis showed that, even though reported case totals were zero throughout 2019 in the Western Cape, horses originating from this province still pose a risk that should not be ignored. Control measures decrease risk by a factor of 2.8 on an annual basis. Not only do the outcomes of this study inform domestic control, they can also be used for scientifically justified trade decision making, since in-country movement control forms a key component of export protocols.
南非是非洲马瘟（AHS）的地方性流行地区，这是一种对马属动物健康和贸易敏感的重要疾病。该国被划分为不同区域，并采取了移动控制措施，以在西南部建立一个无 AHS 的受控区域。我们的目标是通过马匹的合法移动，定量确定 AHS 病毒进入 AHS 受控区的风险。结果被细分为评估风险的移动途径、时间和空间差异。“无控制”情景允许评估控制措施的影响。使用 2019 年的移动和 AHS 病例数据以及全国普查数据，开发了一个随机模型，以建立每月间隔的 AHSV 在当地市政府一级进入的风险。这些数据被汇总为每年的进入概率。敏感性分析评估了模型变量对进入概率条件均值的影响。AHSV 进入南非受控区的每月中值进入概率范围从 0.75%（6 月）到 5.73%（2 月），每年中值进入概率估计为 20.21%（95%CI：15.89%-28.89%）。AHSV 进入受控区的年风险与过去 20 年爆发数据的 AHS 进入受控区的年概率非常吻合，约为 10%。直接非检疫移动构成了大部分移动，占进入风险的大部分。空间分析表明，尽管 2019 年整个西开普省都没有报告病例，但来自该省的马匹仍然存在风险，不容忽视。控制措施每年将风险降低 2.8 倍。这项研究的结果不仅为国内控制提供了信息，还可以用于有科学依据的贸易决策，因为国内移动控制是出口协议的关键组成部分。
