An entry risk assessment of African horse sickness virus into the controlled area of South Africa through the legal movement of equids.
Abstract: 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.
Publication Date: 2021-05-26 PubMed ID: 34038466PubMed Central: PMC8153453DOI: 10.1371/journal.pone.0252117Google Scholar: Lookup
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- Journal Article
- Research Support
- Non-U.S. Gov't
- African Horse Sickness
- Diagnosis
- Disease control
- Disease Diagnosis
- Disease Etiology
- Disease Management
- Disease Outbreaks
- Disease Prevalence
- Disease Surveillance
- Disease Transmission
- Disease Treatment
- Epidemiology
- Equids
- Equine Diseases
- Equine Health
- Horses
- Infectious Disease
- Public Health
- Risk Factors
- Veterinary Medicine
- Veterinary Research
Summary
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The research explores the risk of African horse sickness virus (AHS) entering the controlled area of South Africa through the legal movement of horses. The study uses a stochastic model backed by data from 2019 to estimate the risk and impact of control measures on the occurrence of AHS.
Objective and Methodology
- The primary objective of the research was to quantitatively determine the risk of AHS virus spreading to the AHS-free controlled areas in South Africa through legal horse movement. The risk outcomes were evaluated based on movement pathway, time, and location differences.
- The researchers developed a stochastic model using data from 2019, encompassing movement and AHS case data, and census data from across the nation. This model aimed to establish the risk of the virus entering local municipalities on a monthly basis.
- A ‘no-control’ scenario was also taken into account to evaluate the effectiveness of the existing control measures on the spread of the virus.
Findings
- The research found that the median monthly probability of the AHS virus entering the controlled area varied between 0.75% and 5.73%, with the yearly median probability of entry estimated at 20.21%.
- The annual risk of AHS entry was found to be consistent with the annual probability of the introduction of AHS into the controlled area, which is around 10% based on the data from the past 20 years of outbreak data.
- The highest risk factor was from the direct non-quarantine movements of horses. Despite no cases reported in the Western Cape area in 2019, the horsrs originating from this region still posed a significant risk.
Impact of Control Measures and Implications of the Study
- Control measures were found to reduce risk by a factor of 2.8 annually, thereby highlighting their importance in preventing the spread of AHS.
- Aside from contributing to the understanding of domestic control measures, the study findings could also be used to make scientifically justified trade decisions, since in-country movement control forms a key component of export protocols.
Cite This Article
APA
Grewar JD, Kotze JL, Parker BJ, van Helden LS, Weyer CT.
(2021).
An entry risk assessment of African horse sickness virus into the controlled area of South Africa through the legal movement of equids.
PLoS One, 16(5), e0252117.
https://doi.org/10.1371/journal.pone.0252117 Publication
Researcher Affiliations
- 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.
- 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.
- Veterinary Services, Western Cape Department of Agriculture, Elsenburg, Western Cape Province, South Africa.
- South African Equine Health and Protocols NPC, Cape Town, Western Cape Province, South Africa.
- Department of Veterinary Tropical Diseases, University of Pretoria, Pretoria, Gauteng, South Africa.
MeSH Terms
- African Horse Sickness Virus / pathogenicity
- Animals
- Horses
- Models, Theoretical
- Polymerase Chain Reaction
- South Africa / epidemiology
- Spatial Analysis
Conflict of Interest Statement
SAEHP functions through public private partnership agreement with the Western Cape Department of Agriculture: Veterinary Services. The ECOD case numbers used in this evaluation reflect the reporting system numbers and do not necessarily reflect the official totals as reported by South Africa’s Veterinary Services. The authors have declared that no competing interests exist.
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