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Home / Equine Research Bank / Transbound Emerg Dis / Post-outbreak African horse sickness surveillance: A scenari...
Transboundary and emerging diseases2020; 67(5); 2146-2162; doi: 10.1111/tbed.13566

Post-outbreak African horse sickness surveillance: A scenario tree evaluation in South Africa’s controlled area.

Abstract: An African horse sickness (AHS) outbreak occurred in March and April 2016 in the controlled area of South Africa. This extended an existing trade suspension of live equids from South Africa to the European Union. In the post-outbreak period ongoing passive and active surveillance, the latter in the form of monthly sentinel surveillance and a stand-alone freedom from disease survey in March 2017, took place. We describe a stochastic scenario tree analysis of these surveillance components for 24 months, starting July 2016, in three distinct geographic areas of the controlled area. Given that AHS was not detected, the probability of being free from AHS was between 98.3% and 99.8% assuming that, if it were present, it would have a prevalence of at least one infected animal in 1% of herds. This high level of freedom probability had been attained in all three areas within the first 9 months of the 2-year period. The primary driver of surveillance outcomes was the passive surveillance component. Active surveillance components contributed minimally (<0.2%) to the final probability of freedom. Sensitivity analysis showed that the probability of infected horses showing clinical signs was an important parameter influencing the system surveillance sensitivity. The monthly probability of disease introduction needed to be increased to 20% and greater to decrease the overall probability of freedom to below 90%. Current global standards require a 2-year post-incursion period of AHS freedom before re-evaluation of free zone status. Our findings show that the length of this period could be decreased if adequately sensitive surveillance is performed. In order to comply with international standards, active surveillance will remain a component of AHS surveillance in South Africa. Passive surveillance, however, can provide substantial evidence supporting AHS freedom status declarations, and further investment in this surveillance activity would be beneficial.
© 2020 Blackwell Verlag GmbH.
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Publication Date: 2020-04-21 PubMed ID: 32267629DOI: 10.1111/tbed.13566Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

This research studies the surveillance methods used to monitor African horse sickness (AHS) following an outbreak in South Africa and suggests that international standards for declaring a region free of the disease may be adjusted based on adequate monitoring.

Background of the Study

  • The study emerges from the aftermath of an African horse sickness outbreak that happened in March and April 2016 in South Africa’s AHS controlled area.
  • This outbreak extended the ongoing trade suspension of live equids (horses, donkeys, and their relatives) from South Africa to the European Union.
  • Following the outbreak, varied surveillance methods such as constant passive monitoring and active monthly surveillance, as well as a standalone freedom from disease survey, took place throughout 24 months (from July 2016).

The Methodology Used

  • A stochastic scenario tree analysis was undertaken to evaluate the efficacy of these varied surveillance components over the two-year period.
  • The scenario tree analysis was applied in three distinct geographic regions within the AHS controlled area.

Findings of the Study

  • The research finds that given no detection of AHS, the probability that the regions are free from AHS varies between 98.3% to 99.8%, assuming a prevalence of at least one infected animal in 1% of herds if AHS were present.
  • Furthermore, such high freedom probabilities were achieved in all three areas within the initial 9 months of the two-year analysis period.
  • The findings also point out that passive surveillance was the crucial element influencing the results, while active surveillance contributed minimally (less than 0.2%) to the final probability of freedom from AHS.
  • Sensitivity analysis conducted in the study reveals that the likelihood of infected horses showing clinical signs was a crucial factor impacting the sensitivity of the entire surveillance system.
  • If the monthly chance of disease introduction rises to 20% or more, the overall freedom probability decreases to less than 90%.

Implications and Recommendations

  • The findings indicate that the global standards requiring a 2-year post-outbreak freedom period from AHS could potentially be shortened if efficiently sensitive surveillance is implemented.
  • Nonetheless, in order to comply with international standards, active surveillance will continue being an aspect of AHS monitoring in South Africa.
  • The study suggests that passive surveillance can offer significant evidence in support of AHS free status declarations, and hence, further investment in passive surveillance activities is recommended.

Cite This Article

APA
Grewar JD, Porphyre T, Sergeant ES, Theresa Weyer C, Thompson PN. (2020). Post-outbreak African horse sickness surveillance: A scenario tree evaluation in South Africa’s controlled area. Transbound Emerg Dis, 67(5), 2146-2162. https://doi.org/10.1111/tbed.13566

Publication

Transboundary and emerging diseases
ISSN: 1865-1682
NlmUniqueID: 101319538
Country: Germany
Language: English
Volume: 67
Issue: 5
Pages: 2146-2162

Researcher Affiliations

Grewar, John Duncan
  • Epidemiology Section, Department of Production Animal Studies, Faculty of Veterinary Science, University of Pretoria, Onderstepoort, South Africa.
  • South African Equine Health and Protocols NPC, Baker Square, Cape Town, South Africa.
Porphyre, Thibaud
  • The Roslin Institute, University of Edinburgh, Edinburgh, UK.
Sergeant, Evan S
  • AusVet Animal Health Services, Canberra, ACT, Australia.
Theresa Weyer, Camilla
  • South African Equine Health and Protocols NPC, Baker Square, Cape Town, South Africa.
  • Department of Tropical Diseases, Faculty of Veterinary Science, University of Pretoria, Onderstepoort, South Africa.
Thompson, Peter Neil
  • Epidemiology Section, Department of Production Animal Studies, Faculty of Veterinary Science, University of Pretoria, Onderstepoort, South Africa.

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Citations

This article has been cited 1 times.
  1. Grewar JD, Kotze JL, Parker BJ, van Helden LS, Weyer CT. An entry risk assessment of African horse sickness virus into the controlled area of South Africa through the legal movement of equids. PLoS One 2021;16(5):e0252117.
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