African Horse Sickness - Final Report
The African Horse Sickness (AHS) serotype 1 outbreak was resolved on 17 June 2014 just over three months after the initial veterinary control notice was released as a result of positive cases detected in the Porterville region of the Western Cape AHS Protection Zone.
The outbreak was initially limited to the AHS protection zone but further cases eventually spread to the AHS surveillance zone. The initial containment zone was amended twice, and eventually included the Porterville, Wellington, Piketberg and Tulbagh regions.
AHS cases in Robertson were detected in early April 2014 and during the outbreak this was treated as a separate event given the distance from Porterville and no proof of spread of infection via the movement of infected horses.
In this report however we merge the two areas to include all cases under the same outbreak. Although the movement link between the two main areas of cases could not be made with clinical signs (or lack thereof), low mortality and low morbidity has been similar throughout.
In total there were 36 affected properties. We had 96 confirmed cases. To give an indication of the lack of clinical signs associated with this outbreak: the total number of deaths came to 12 giving a case fatality rate of 12.5%. The total number of sub-clinical cases made up 60 of the 96 cases, showing a sub clinical rate of 62.5%. We are still evaluating our census data but even if we just look at the number of horses on the 36 positive farms (which totalled 866 horses); the morbidity rate was only 11%. In reality this number is going to drop significantly once our full census data is captured for the outbreak areas.
The above figures are not what we would expect from an AHS outbreak as normally the morbidity, mortality and case fatality rates are significantly higher.
There are four other areas within the Province where AHS cases have also occurred this season: Leeu Gamka, Murraysburg, Beaufort West and Uniondale. These (all non-AHS serotype 1) cases are not linked to the Protection and Surveillance zone cases.
We want to thank the officials, private veterinarians and members of the public who assisted in controlling this outbreak.