Information of the AHS outbreak in the Protection Zone of South Africa - Cederberg 2021

The outbreak

The outbreak of African horse sickness (AHS) started in April 2021 and was first detected through the passive clinical surveillance program in place in the controlled area. The outbreak was active in the AHS Protection Zone east of the Cederberg mountains along the R364, with a single property affected just over the Pakhuis pass on the western slopes of the Cederberg. In total 4 properties were affected with 37 cases being reported.

The outbreak was resolved and movement restrictions lifted on 6 July 2021, 40 days after the last reported case.

Data considerations and Disclaimer

We make every effort to provide as up to date information as possible in this website. The disease reporting process in an outbreak like this originates from the initial notification of a case (through a laboratory report or field report - see Case definition below), to get verified by Provincial Veterinary Services. It then gets submitted to National Veterinary Services who report finally to the OIE (World Organisation for Animal Health). Official South African Government case totals would be those that are reported to the OIE. There is therefore, particularly in the begining phases of an outbreak, a lag between field associated cases and officially reported cases. This website may therefore include cases that have not been officially reported and the data and information should be treated with that in mind. For official statistics please consult the outbreak report on the OIE website.

Case definition during this outbreak

The positive case definition is based on OIE prinicples for infection with African horse sickness. All cases reported here fall into one of the positive categories below:
  • Positive 1: [Clinical and/or post-mortem signs consistent with AHS] AND [laboratory PCR and/or virus isolation positive results]
  • Positive 2: [Laboratory PCR and/or virus isolation positive results only]
  • Positive 3: [Clinical and/or post-mortem signs consistent with AHS with no lab positive confirmation] AND [epidemiologic links to positive cases]

Below is a brief overview of case totals and other aggregated outbreak data.
Note: Status is based on both clinical and testing surveillance

Active investigation zone stats

Lab test status - all diseases

Outbreak investigated holdings

Outbreak investigated equids

Outbreak controlled areas were designated in the outbreak and changed as the outbreak progressed.
  • The LAYERS button on the top right of the map allows layers to be toggled on and off
  • Details of control measures are found below the map
  • Outbreak response plans detail the spatial areas where specific response measures were implemented
  • To get more information on a specific layer: deselect other layers on the top right of the map and click on the area you'd like more info on

Outbreak control zones

Different outbreak zones were used:
  • Active investigation zones AIZ contained all active cases and had intense surveillance and investigation in those areas
  • Outbreak control zones OCZ encompass all prior cases. Less intense surveillance is applied here and clinical/passive surveillance by horse owners/managers is the primary mechanism of detecting new cases and secondary spread. OCZ's generally indicate where movement restrictions are in place
  • The AHS controlled area of South Africa refers to the area legislated in the Animal Diseases Act where AHS is not considered endemic

15 April 2021

The WCDOA Veterinary services control directive for the initial outbreak are available - click on the link to access

Vaccination during the outbreak was prohibited in the outbreak controlled area and due to the time of year by extension in the whole AHS controlled area (see map above)

DALRRD also delayed the start (from 1 June to 1 July) of the vaccination season in the AHS controlled area

Advice to owners

  • All horse owners/managers were encouraged to stable their horses from two hours before sunset to two hours after dawn to decrease the vector (midges) of the disease from having contact with their horses.
  • A registered insect repellent and insecticide for use in horses would also decrease the risk of infection and spread of the disease and the use of these products were encouraged.
  • Horse owners/managers and vets were requested to report any equines with unexplained fever, swelling of the head and neck, and difficulty in breathing to their local State Veterinarian.

06 July 2021

The WCDOA Veterinary services resolution of the outbreak can be accessed here

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Run analysis

Epidemic curves allow the analysis of outbreaks in time - i.e. a temporal analysis of data. While the output of an epidemic curve is relatively straightforward, the benefit of such analysis allows the determination of:
  • Establishing the probability of the detection of the actual first case in the outbreak
  • Establishing the rate of progression and temporal trends of the outbreak
  • Identifying the secondary/progressive spread of infection
  • Establishing the impact of control measures

Select date range of interest

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Run analysis

Click on an affected area for more information

Spatial analysis of outbreaks allows the determination of how an outbreak spreads and the impact it has on specific areas. Analysis is aggregated to 50km hexagons.

In the map there are two outputs that assist in spatial analysis:
  • The number of cases reported per area (density of outbreak)
  • The week of the outbreak (week of the year 2021) that any affected area was first affected, which shows how spread has taken place
The LAYERS button on the top right of the map allows layers to be toggled on and off.