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PloS one2019; 14(10); e0222366; doi: 10.1371/journal.pone.0222366

Assessing the potential of plains zebra to maintain African horse sickness in the Western Cape Province, South Africa.

Abstract: African horse sickness (AHS) is a disease of equids that results in a non-tariff barrier to the trade of live equids from affected countries. AHS is endemic in South Africa except for a controlled area in the Western Cape Province (WCP) where sporadic outbreaks have occurred in the past 2 decades. There is potential that the presence of zebra populations, thought to be the natural reservoir hosts for AHS, in the WCP could maintain AHS virus circulation in the area and act as a year-round source of infection for horses. However, it remains unclear whether the epidemiology or the ecological conditions present in the WCP would enable persistent circulation of AHS in the local zebra populations. Here we developed a hybrid deterministic-stochastic vector-host compartmental model of AHS transmission in plains zebra (Equus quagga), where host populations are age- and sex-structured and for which population and AHS transmission dynamics are modulated by rainfall and temperature conditions. Using this model, we showed that populations of plains zebra present in the WCP are not sufficiently large for AHS introduction events to become endemic and that coastal populations of zebra need to be >2500 individuals for AHS to persist >2 years, even if zebras are infectious for more than 50 days. AHS cannot become endemic in the coastal population of the WCP unless the zebra population involves at least 50,000 individuals. Finally, inland populations of plains zebra in the WCP may represent a risk for AHS to persist but would require populations of at least 500 zebras or show unrealistic duration of infectiousness for AHS introduction events to become endemic. Our results provide evidence that the risk of AHS persistence from a single introduction event in a given plains zebra population in the WCP is extremely low and it is unlikely to represent a long-term source of infection for local horses.
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Publication Date: 2019-10-31 PubMed ID: 31671099PubMed Central: PMC6822716DOI: 10.1371/journal.pone.0222366Google 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 article explores the likelihood of the plains zebra population in South Africa’s Western Cape Province (WCP) maintaining a continued presence of African horse sickness (AHS). The researchers found that the risk of AHS persisting in these zebra populations due to an initial introduction of the disease is exceedingly low, suggesting that these zebras are unlikely to be a constant source of infection for local horses.

Study Aim and Methodology

  • AHS is a harmful disease affecting horses and similar species, which can impose financial and trade obstacles for countries where it is endemic, including South Africa.
  • The goal of this study was to examine the probability of plains zebras, often thought to be the natural hosts of AHS, sustaining AHS circulation in the WCP. This was an area of concern as continuous disease transmission could potentially infect horses year-round.
  • The authors developed a hybrid deterministic-stochastic vector-host compartmental model of AHS transmission in plains zebra to assess this risk.
  • This sophisticated model took into account the age, sex composition of zebra populations, as well as the influence of rainfall and temperature conditions on the population and AHS transmission dynamics.

Findings

  • The model revealed that the current size of the zebra population in the WCP is too small for a single introduction of AHS to become endemic.
  • Coastal zebra populations would need to exceed 2,500 for AHS to persist longer than two years, even if zebras were infectious for over 50 days.
  • A zebra population of at least 50,000 would be required for AHS to become endemic in the province’s coastal region.
  • In contrast, the inland zebra populations potentially pose a risk for AHS persistence, but they would require a minimum of 500 individuals, or show an unrealistically extended duration of infectiousness, to enable the disease to become endemic.

Implications

  • The findings featured in this study significantly decrease the concern about plains zebras being a constant source of AHS infection for horses in the WCP.
  • According to the results, the likelihood of a single AHS introduction causing the disease to persist in the local zebra population is extremely low, unless the zebra population is significantly larger than current estimates.
  • This research provides valuable information for future disease control and prevention measures in the region, improving the health and welfare of both the zebra and horse populations in the WCP.

Cite This Article

APA
Porphyre T, Grewar JD. (2019). Assessing the potential of plains zebra to maintain African horse sickness in the Western Cape Province, South Africa. PLoS One, 14(10), e0222366. https://doi.org/10.1371/journal.pone.0222366

Publication

PloS one
ISSN: 1932-6203
NlmUniqueID: 101285081
Country: United States
Language: English
Volume: 14
Issue: 10
Pages: e0222366

Researcher Affiliations

Porphyre, Thibaud
  • The Roslin Institute, University of Edinburgh, Edinburgh, Scotland, United Kingdom.
Grewar, John D
  • South African Equine Health & Protocols NPC, Paardevlei, Cape Town, South Africa.

MeSH Terms

  • African Horse Sickness / pathology
  • African Horse Sickness / transmission
  • African Horse Sickness / virology
  • African Horse Sickness Virus / pathogenicity
  • Animals
  • Disease Outbreaks
  • Equidae / virology
  • Horse Diseases / epidemiology
  • Horse Diseases / virology
  • Horses / virology
  • Insect Vectors / virology
  • South Africa

Conflict of Interest Statement

The authors have declared that no competing interests exist.

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Citations

This article has been cited 4 times.
  1. de Klerk JN, Gorsich EE, Grewar JD, Atkins BD, Tennant WSD, Labuschagne K, Tildesley MJ. Modelling African horse sickness emergence and transmission in the South African control area using a deterministic metapopulation approach. PLoS Comput Biol 2023 Sep;19(9):e1011448.
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  2. Myburgh A, Lambrechts H, Hoffman LC. A Descriptive Study on the Carcass, Muscle, and Offal Yields of the Plains Zebra (Equus quagga) Harvested in Two Seasons. Animals (Basel) 2022 Dec 22;13(1).
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  3. Nelson E, Thurston W, Pearce-Kelly P, Jenkins H, Cameron M, Carpenter S, Guthrie A, England M. A Qualitative Risk Assessment for Bluetongue Disease and African Horse Sickness: The Risk of Entry and Exposure at a UK Zoo. Viruses 2022 Feb 28;14(3).
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  4. Clemmons EA, Alfson KJ, Dutton JW 3rd. Transboundary Animal Diseases, an Overview of 17 Diseases with Potential for Global Spread and Serious Consequences. Animals (Basel) 2021 Jul 8;11(7).
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