African Horse Sickness: A Risk Map For West African Horse Owners

African horse sickness (AHS) is a midge-borne viral disease of equids that is endemic across sub-Saharan Africa, including Nigeria. It kills many unprotected horses. No fine-scale risk map was found in the sources retrieved, so this article sets out what the published evidence does show.

How it spreads

Culicoides biting midges transmit the virus. Iowa State's disease factsheet names two species as known African vectors and states that direct contact does not spread the disease. Zebras often carry infection without signs, and the Nigerian authors also describe donkeys as silent reservoirs. Incubation is usually under nine days, with a range of two days to two weeks.

How severe it is

Severity depends on the form. The pulmonary form is close to 100 per cent fatal, the cardiac form kills 50 per cent or more, and the mixed form 70 to over 80 per cent. Across naive horses in outbreaks, the factsheet gives a range of 50 to 95 per cent. A mild fever form also exists.

What is known about West Africa

The Merck Veterinary Manual describes the disease as endemic from Senegal to Ethiopia and Somalia. Evidence from individual countries is mostly antibody surveys:

• Nigeria: a 2025 study tested 575 horses from five locations and found antibodies in 89.9 per cent. Rates ran from 75 per cent in Oyo to 100 per cent in Enugu. The authors could not separate infection from vaccination, and they noted a recent outbreak in Lagos State.
• The Gambia: a 2009 survey of 144 equids found 96 per cent with antibodies and serotype 9 only. The virus matched a live vaccine strain, and no clinical disease was seen.

These surveys show exposure. They do not show how many horses became ill. Sahel-specific data were not found.

Seasonality and control

Merck links outbreaks to heavy rain followed by hot, dry weather, which suits midges. Vaccination with live attenuated vaccine is the main control in endemic countries, but it must match circulating serotypes and carries concerns about reversion. Stabling at peak midge activity and repellents are described as supporting measures. A veterinarian advises on any plan.

What this means for the programme

Sahel mares are crossed with thoroughbred sires, using frozen semen under an import permit with a batch record. Each animal is microchipped, with DNA parentage and a veterinarian's sign-off, and a written start record is kept. The programme is in formation. No ponies are for sale, and no results are claimed yet.

Frequently asked questions

Is Nigeria free of AHS? No. The 2025 study concluded the disease is widespread in horses there.

Does a positive antibody test mean a horse was ill? Not necessarily. Antibodies can come from infection or vaccination, and the surveys cited did not separate them.

Can AHS pass directly from horse to horse? The Iowa State factsheet says direct contact does not spread it. Midge bites do.