African Horse Sickness

This is a highly infectious and deadly disease that commonly effects horses, mules and donkeys.


AHSV was first recorded south of the Sahara Desert in the mid 1600s with the introduction of horses to southern Africa.

African horse sickness was diagnosed in Spain in 1987-90 and in Portugal in 1989, but was eradicated using slaughter policies, movement restrictions, vector eradication and vaccination.


AHS is not directly contagious but spreads mostly via the midge but can also be spread by mosquitos or many other insects. Larvae do not carry the virus and long, cold winters are sufficient to break epidemics in non-endemic areas.

Horses are the most susceptible host with close to 90% mortality of those affected, followed by mules (50%) and donkeys (10%). African donkeys and zebras very rarely display clinical symptoms, despite high virus titres in blood, and are thought to be the natural reservoir of the virus.

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.


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.

Inoculation Period:

The inoculation period for AHS is six weeks long and involves the horse getting two injections that effects the horse three weeks each. This inoculation process protects the horse against the most common strains of the season and is enforced by law. Horses not inoculated are not allowed to compete.
During this process horses build antibodies which puts strain on them and a specific work routine is followed. This routine is mostly light work involving walking and keeping their heart rate down.

Images of AHS: