The 2011 outbreak of African horse sickness in the African horse sickness controlled area in South Africa

John D. Grewar,Sewellyn Davey,Gary Bührmann,Dawid Visser,Alan J. Guthrie,Melvyn Quan,Camilla T. Weyer,Pieter Koen,Esthea Russouw

doi:10.4102/jsava.v84i1.973

John D. Grewar, Sewellyn Davey + Show 7 more

Open Access

https://doi.org/10.4102/jsava.v84i1.973

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Abstract

African horse sickness (AHS) is a controlled animal disease in South Africa, and as a result of the high mortality rates experienced, outbreaks in the AHS controlled area in the Western Cape Province have a significant impact on affected properties as well as on the exportation of live horses from the AHS free zone in metropolitan Cape Town. An outbreak of AHS serotype 1 occurred in the surveillance zone of the AHS controlled area of the Western Cape during the summer of 2011. The epicentre of the outbreak was the town of Mamre in the magisterial district of Malmesbury and the outbreak was confined to a defined containment zone within this area by movement control of all equids and a blanket vaccination campaign. A total of 73 cases of AHS were confirmed during this outbreak, which included four confirmed subclinical cases. The morbidity rate for the outbreak was 16%with a mortality rate of 14%and a case fatality rate of 88%. Outbreak disease surveillance relied on agent identification using polymerase chain reaction (PCR)-based assays, which is novel for an AHS outbreak in South Africa. The source of this outbreak was never confirmed although it is believed to be associated with the illegal movement of an infected animal into the Mamre area. This detailed description of the outbreak provides a sound scientific basis to assist decision making in future AHS outbreaks in the AHS controlled area of South Africa and in countries where AHS is an exotic or emerging disease.

Highlights

African horse sickness (AHS) is a vector-borne, life threatening disease of equids caused by African horse sickness virus (AHSV), a member of the genus Orbivirus in the family Reoviridae
On 26 February 2011, State Veterinarian (SV) Malmesbury was requested by a private veterinarian from the Malmesbury district to assist in the necropsy of a horse that had died that day in the town Mamre in the Western Cape Province of South Africa
The State was able to start vaccinations immediately with the AHS vaccine donated by the Equine Research Centre and the personnel of the different bodies were able to work together in an efficient manner

Summary

Introduction

African horse sickness (AHS) is a vector-borne, life threatening disease of equids caused by African horse sickness virus (AHSV), a member of the genus Orbivirus in the family Reoviridae. This virus causes vascular injury that can result in four forms of disease: the pulmonary, cardiac, mixed, or horse sickness fever forms (Erasmus 1974). AHS is endemic to sub-Saharan Africa but the disease has occurred sporadically outside of this region (Mellor 1994), for example the outbreaks of AHS in Spain in the 1960s and 1980s, where hundreds of horses succumbed to the disease while hundreds of thousands were vaccinated during its control (Rodriguez, Hooghuis & Castano 1992)

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