African Horse Sickness Vaccination: What the Research Shows

Introduction

African Horse Sickness (AHS) is a serious viral disease of equids in sub-Saharan Africa. Because vaccination is a key preventive tool, owners often ask when to vaccinate and what different vaccines cover. This article summarises peer-reviewed research and official guidance so you can discuss options with your veterinarian using verified information.

1. The Virus and Its Transmission

• AHS is caused by African horse sickness virus (AHSV), an orbivirus in the family Reoviridae.
• There are nine recognised serotypes of AHSV.
• The virus is transmitted primarily by Culicoides biting midges; transmission risk increases with warm, humid conditions and areas with standing water. Occasional transmission by mosquitoes and ticks has been documented but is uncommon.

Sources: Merck Veterinary Manual; peer-reviewed reviews on AHSV epidemiology (see References).

2. Vaccines in Use (Southern Africa)

A commonly used vaccine in southern Africa is a polyvalent live-attenuated vaccine (LAV) produced by Onderstepoort Biological Products (OBP). It is supplied as two vials administered several weeks apart, each covering different serotypes:

• Vial 1: serotypes 1, 3, 4
• Vial 2: serotypes 2, 6, 7, 8

These vials are not “booster” and “primary” for each other; they broaden coverage across multiple serotypes. Specific protocols (sequence and interval) should be set in consultation with your veterinarian and according to current product literature.

Sources: University of Pretoria Equine Research Centre newsletter; peer-reviewed literature on OBP LAV (see References).

3. Regulatory Oversight in South Africa

Veterinary medicines sold in South Africa must be registered with the South African Health Products Regulatory Authority (SAHPRA). Registration entails a documented assessment of quality, safety, and efficacy in line with SAHPRA guidelines. Registered products carry identifiers (often referenced by practitioners) that indicate they have undergone formal review.

• Owners can ask their vet or supplier to confirm that a product is registered.
• Registration includes requirements for appropriate manufacturing and quality control.

Sources: SAHPRA registration and guideline documents (see References).

4. Timing Considerations

Because AHS is vector-borne, vaccination programmes are planned to allow time for the immune response to develop before local midge activity increases. Exact dates vary by region and year (rainfall, temperature, and local ecology influence midge populations). Work with your veterinarian on a schedule appropriate for your area and be aware of any province- or zone-specific rules that may apply to controlled areas.

Key points supported by research:

• Vector activity (especially Culicoides midges) is the major driver of infection risk.
• Correct vaccine handling (cold chain), dosing, and intervals influence immune responses.

Sources: peer-reviewed AHS reviews; vaccine immunogenicity studies (see References).

5. Stable and Environmental Measures

Vaccination should be paired with practical management steps to reduce midge exposure:

• Reduce standing water and fix leaking taps.
• Use fine-mesh netting or screened stables where feasible.
• Stable horses during peak midge times (typically dusk and dawn) when appropriate for your management system.
• Use registered repellents and follow label directions.

Sources: veterinary manuals and vector-control guidance (see References).

6. Discussing a Schedule With Your Veterinarian

• Confirm the vaccine product and which serotypes it covers (two-vial system for OBP LAV).
• Plan timing relative to expected vector season in your district.
• Ensure correct storage and handling (cold chain) and observe manufacturer intervals between doses.
• For foals, pregnant mares, and imports, follow veterinary guidance and current vaccine literature.