Observations on antibody levels associated with active and passive immunity to African horse sickness.

The research examines the effectiveness of African horse sickness (AHS) virus vaccinations in horses and suggests more vaccinations can improve response to various serotypes, but a naturally occurring infection gives the highest antibody titres. It recommends early immunisation in foals, as maternally acquired antibodies can decline rapidly.

Research Overview

• The research focused on studying neutralising (NT) antibodies to the nine serotypes of African horse sickness (AHS) virus in three groups of horses.
• The researchers confirmed that increasing the number of vaccinations lead to a broader response to the different serotypes and higher individual antibody titres.
• The study found variations in individual horse responses, with some horses not responding to one or more serotypes despite receiving several immunizations.

Limitations of the Current Vaccine

• The research made it clear that the vaccine containing only serotypes 1 to 6 wasn’t sufficient to induce cross-immunity to serotypes 7 to 9 of the virus.
• Thus, it can’t be entirely counted on to provide full protection against all forms of the AHS virus.

Insight from Natural Infections

• A fourth group of horses that had suffered a natural infection demonstrated the highest antibody titres and broadest cross-reactivity.
• This suggests that natural exposure provides a more comprehensive protection compared to the existing vaccinations.

Foals and their Immune Response

• The researchers also observed the levels of antibodies from colostrum in seven foals. They found that there was generally a correlation with the antibody levels in the serum of the foals’ mothers.
• However, some instances showed that antibodies to individual serotypes of virus can decline to undetectable levels within two to four months from birth.
• This implies that susceptibility to infection could occur before the commonly recommended age (six to nine months) for initial immunisation.

Vaccination of Foals

• Early vaccination of foals (three to four months of age) resulted in a weak antibody response. However, it didn’t adversely affect the pre-existing low levels of maternal antibody.
• The research recommends early immunisation for foals, indicating that this could be an effective way to control the losses experienced in Zimbabwe due to this disease.