African Horse Sickness is an annual seasonal problem that occurs because of the carrier – Culicoides midges, that build up in numbers during the spring/summer period.

 SA has experienced two very wet summer seasons in 2009 and 2010. We have already seen the first rains in 2011 and the midges will be starting to increase in numbers.

The disease is feared by horse owners because of the very distressing consequences, should a horse develop AHS and die from the acute form – Dunkop. OBP provides the only vaccine available to horse owners and the vaccination of horses is a critical step in trying to protect horses. The incubation period of the disease is short (–typically 5 to 7 days) - the horse shows a high fever, anorexia and then what is termed the “Dunkop” or the Dikkop” form of the disease.

The Culicoides midges that transmit the disease are very aggressive bloodsuckers and their bites cause intense irritation to horses, which is often recognized as a complex - Sweet Itch. The midges are night-biting midges and if a horse is not stabled, it will be exposed to the typical level of irritation seen in a video produced by the Department of Agriculture, Forestry and Fisheries of another midge that bites near the Orange River. The midges have to obtain a blood meal to be able to reproduce, and will obtain the blood meal from any livestock available e.g. cattle, sheep etc., but seem to prefer larger animals.

The options available to protect horses include insecticides and repellents; barrier techniques e.g. Fly Sheets and masks, screens on stable doors and windows and stabling of horses at night. The primary protection relies on vaccination with the OBP vaccination and in some areas where it is possible, the horses are moved to high ground where the numbers of midges are expected to be much lower.

Stride provides the following products:

1. Fly/Mosquito Sheets, made from a form of plastic which together with Fendona Wettable Powder which is sprayed on the Fly Sheet, so that should any midges land on the Fly Sheet, they will be killed.
   
   
2. Equiworld Fly Repellent has a claim for killing mosquitoes – based upon trial work to show that this product is effective. However, the duration of protection of horses treated with Equiworld Fly Repellent is unlikely to exceed 24 hours during the season, thus daily treatments need to be applied.

If the Fly Sheets and Equiworld Fly Repellent are combined, this can be expected to provide the best level of protection. Horses must be stabled at night and if screens can be installed, in stables to protect from midges entering the stables, this will reduce the opportunity for the midges to obtain a blood meal from the horses (and at the same time transmit the virus).