Veterinarians with masks giving vaccine to the horse

An effective vaccine protecting against all nine strains of African Horse Sickness Virus (AHSV) is a step closer, according to new research.

The virus has devastating effects on horse populations across sub-Saharan Africa and there have also been outbreaks in Spain and Portugal.

A study, led by the London School of Hygiene & Tropical Medicine and funded by the UK-based Biotechnology and Biological Sciences Research Council (BBSRC), used a type of vaccine that possesses all the benefits of a traditional vaccine with none of the associated risk factors.

The researchers’ work is the first to report a reverse genetics-based vaccine for African Horse Sickness Virus.

African Horse Sickness causes severe respiratory problems and approximately 90% of horses that catch it die within a week.

The biting midges that transmit the disease are found all across Europe and there is concern regarding the influence of climate change on midge populations.

Many countries use a ‘live’ vaccine to treat AHSV. These vaccines render pathogens harmless, vastly reducing their ability to infect a host.

However, there are concerns about the possibility of the virus becoming infectious again due to mutations.

In 2016, the school-led research team developed a reverse genetics system that enabled strains to mimic viruses, demonstrating their same abilities to enter host cells and initiate an immune response.

However, unlike the natural virus the vaccine strains are unable to replicate, rendering them harmless. This ‘Entry Competent Replication-Abortive’ (ECRA) system allowed for the development of virus strains for all nine types of AHSV and a successful mouse model displayed the potential for vaccine development.

In the latest study, researchers tested the effectiveness of a single vaccine strain and a ‘cocktail’ of multiple ECRA-based vaccine strains in eight ponies.

The vaccine viruses were able to enter the cell, triggering strong immune responses but were unable to replicate. None of the eight ponies suffered any adverse effects from the vaccine.

When infected, all vaccinated ponies were protected from African Horse Sickness and only the non-vaccinated ponies had clinical symptoms of virus infection.

Principal study investigator Polly Roy, Professor of Virology at the London School of Hygiene & Tropical Medicine, said: “The high volume of movement in the horse industry increases the risk of the introduction of exotic diseases such as African Horse Sickness. There are well-designed control measures for animal outbreaks in the UK, but measures taken during such an epidemic, such as the restriction of movement, could cost the UK economy approximately £4 billion.

“Using our patented reverse genetics system, the study findings demonstrated that ECRA vaccines triggered strong immune responses in ponies that protected them completely against the virus infection. Our unique and cost-effective vaccine design could act as an example for the development of next generation of vaccines against other vector-borne diseases that undermine the horse industry.”

It is hoped that the development of a safe and effective African Horse Sickness Virus vaccine can afford protection preventing major impact in the event of an outbreak in European countries.