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.
