African Horse Sickness
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About the African Horse Sickness Trust

The AHS Trust and the key role players involved with combating the threat of AHS to the SA equine community joined forces at two workshops held recently. Those present were: Onderstepoort Biological Products, Onderstepoort Veterinary Institute, Faculty of Veterinary Science, Equine Research Center, Department of Agriculture and various other specialists. The first workshop hosted by Equine Research Center and International Livestock Research Institute was aimed at initiating an Economic Impact Study of African Horse Sickness in South Africa. The second three-day scientific workshop hosted by Onderstepoort Biological Products was to establish a collaborative effort by all the institutions involved with research and development of new vaccines. This was the first time all the role players and the equine industry represented by the AHS Trust and Racing South Africa have come together in an effort to address the ever-increasing AHS problem in South Africa. Key aspects that were identified were:

  • Increasing the vaccine coverage of the national herd,
  • Better reporting of the disease,
  • Better cooperation by all role players in an effort to bring a new improved vaccine to the market, and
  • Increase emphasis on scientific research into the epidemology of AHS.

Very important information came to light at these workshops, which the AHS Trust undertook to pass on to the equine community. It is hoped that this will assist with combating AHS outbreaks and protecting our horses from possible infection by the virus.

Currently, approximately only 50% of the national herd of horses is vaccinated, many of which have inadequate immunity due to ignorance or non-compliance of the recommended vaccination procedures. As a result, the risk to the inoculated herd increases dramatically and the Trust urges all horse owners to routinely vaccinate under the following conditions:

  • Where possible use professional veterinary services.
  • Ensure that the cold chain is not broken prior to administering the vaccine.
  • Ideally vaccinate during the low vector activity period (August – October). This ensures that optimal vaccine immunity is provided during the high-risk period of March and April.

This increased vaccine coverage will reduce the impact of outbreaks and the risks of the rapid spread of the disease in high-risk periods.

Protective Measures
Apart from vaccination, horse owners should consider the following additional measures to reduce exposure to the disease:
  • Stable horses when the vector is most active i.e. from late afternoon to mid morning.
  • Cover all access points in the stable with 80% shade cloth – it has been proven to reduce the midge activity inside the stables up to 14 times. For horses living out, shade cloth awnings could be built and horses enclosed during the night.
  • Place fans in stables:
  • Midges are attracted to horse odors and the carbon dioxide emission of the horses – a fan will assist in dispersing the odor trail.
  • Midges are very light and appropriately directed air movement makes it difficult for them to enter stables and/or to stay immobile long enough to feed.

The spread of the disease is directly linked to the midge activity in the area and this is dependant of a number of conditions, rainfall, and temperature and soil types. Areas that have sandy soils seem to have less midge activity as areas with clay based soils. The high rainfall we have been experiencing increases the breeding cycle of the vector and therefore increases the transmission of the disease.

  • Smoking drums at stables – this seems to have no effect on midge activity.
  • Repellants - may assist in reducing the number of midges feeding, but is not guaranteed or necessarily adequate to protect animals completely.
  • Garlic supplements – no scientific evidence that supports this.
  • Moving horses to higher ground – depending on other factors, midges can operate at altitude.
  • Previously vaccinated horses can be worked normally during the vaccination period only if no febrile reaction to the vaccine is indicated. Horses receiving their first AHS vaccine should not be exercised or only minimally exercised during the 6-week vaccination period.

AHS Outbreak reporting 2006/2007
The AHS Trust has once again undertaken to assist the Department of Agriculture with the reporting of outbreaks. It is critical that all cases are reported as they occur, as the movement of infected horses or horses incubating the disease will lead to the spread of virus to areas previously free of the disease. This is especially critical when moving horses into the Controlled Area of the Western Cape as South Africa’s export status depends on maintaining the freedom of this area. All cases must be reported either to the local State Veterinarian and/or the AHS Trust (AHS Trust contact details). The official disease reporting forms are available from the State Vet or from the AHS Trust. Please ensure that they are filled in correctly, with all information requested and returned promptly.

The Trust, The Equine Research Center and volunteers are currently implementing a blanket vaccination program in rural and outlying high-risk areas to try to reduce the impacts and the possible spread of AHS during this next outbreak.
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