Summer brings with it the South African horse owner's curse – African Horse Sickness. Caused by a virus that is transmitted by midges, it remains a condition feared by all who own horses. The main weapons in our arsenal to protect our horses against AHS, are vaccination and midge control.
Vaccination
Vaccination is the first important step. Ignore the stories that the vaccine is ineffective, or that vaccination was invented to make big companies even bigger! The only vaccine available is manufactured and marketed by Onderstepoort Biological Products, and comes in two separate vials. Nine different serotypes of the virus have been identified, and the vaccine contains seven of these.
The first vial contains cell culture-attenuated strains of serotypes 1, 3 and 4 and the second vial serotypes 2, 6, 7, and 8. The two vials should be injected at least three weeks apart. It is advisable to, in young foals that are vaccinated for the first time, rather start with vial 2, and follow up three weeks later with vial 1. The reason for this is that the body's immune system takes a bit longer to react to serotype 3, and this could interfere with the reaction to vial 2.
Keep in mind that the body has to react to each of the seven serotypes separately, and that different levels of antibodies may be induced in different horses, which may play a critical role in the overall immunity/protection against AHS.
Midge control
It is well proven that the midges that transmit AHS in South Africa are predominantly one species of the culicoides midge, C. imicola. The female midge is the bloodsucker. During her lifetime she produces about four batches of approximately 60-160 eggs per batch.
The female midge is driven by a ravenous urge to obtain a blood meal, as she can only start laying eggs after she has fed. It is therefore understandable that most insect repellents are either not entirely effective or do not protect the host animal from being bitten by midges for any duration. It is also known that the preferred area of feeding is about 70% on the dorsal area of the horse and only about 28% on the belly.
How can I protect my horse?
• Stable all horses at night. There should be barriers to prevent insects entering the stable.
• Alternatively a protective shield can be placed on the horse (e.g. a total body coat).
• Install an overhead fan to disperse the odours and carbon dioxide from the horse (these enable the midges to find the horse).
• Apply a registered fly repellent to the horse every evening (before it goes into the stable) and concentrate on treating the dorsal areas.
• Keep horses away from low-lying areas and swamps or dams, as these are midge-breeding areas.
• Consider erecting an ultraviolet light trap outside the stable, to reduce the number of midges.
