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Transbound Emerg Dis. 2019 Mar;66(2):743-751. doi: 10.1111/tbed.13077. Epub 2018 Dec 3.

A field investigation of an African horse sickness outbreak in the controlled area of South Africa in 2016.

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Epidemiology Section, Department of Production Animal Studies, Faculty of Veterinary Science, University of Pretoria, Onderstepoort, South Africa.
Equine Health Fund, Wits Health Consortium, Parktown, South Africa.
Equine Research Centre, Faculty of Veterinary Science, University of Pretoria, Onderstepoort, South Africa.
Epidemiology, Parasites and Vectors, Agricultural Research Council- Onderstepoort Veterinary Research, Onderstepoort, South Africa.
Western Cape Veterinary Services, Elsenburg, South Africa.


An outbreak of African horse sickness (AHS) caused by AHS virus type 1 occurred within the South African AHS surveillance zone during April and May 2016. The index case was detected by a private veterinarian through passive surveillance. There were 21 cases in total, which is relatively low compared to case totals during prior AHS outbreaks in the same region (and of the same AHS virus type) in 2004, 2011 and 2014. The affected proportion of horses on affected properties was 0.07 (95% CI 0.04, 0.11). Weather conditions were conducive to high midge activity immediately prior to the outbreak but midge numbers decreased rapidly with the advent of winter. The outbreak was localized, with 18 of the 21 cases occurring within 8 km of the index property and the three remaining cases on two properties within 21 km of the index property, with direction of spread consistent with wind-borne dispersion of infected midges. Control measures included implementation of a containment zone with movement restrictions on equids. The outbreak was attributed to a reversion to virulence of a live attenuated vaccine used extensively in South Africa. Outbreaks in the AHS control zones have a major detrimental impact on the direct export of horses from South Africa, notably to the European Union.


Culicoides ; African horse sickness type 1; South Africa; disease outbreak; horses

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