Major strides in developing vaccines against deadly African Horse Sickness


A new vaccine design shows great promise in protecting against multiple strains of the deadly African Horse Sickness Virus.

The study used a type of vaccine that is said to have all the benefits of a traditional vaccine with none of the associated risk factors.

The study team developed vaccines against all nine serotypes of the African Horse Sickness Virus and reported that combinations of them have proven to be effective.

The researchers from the London School of Hygiene & Tropical Medicine are the first to report a “reverse genetics”-based vaccine for the virus and highlights its great potential in controlling the disease.

African Horse Sickness affects species in the horse family. It causes severe respiratory problems and about 90% of horses that catch it die within a week.

It is endemic to sub-Saharan Africa although there have also been known outbreaks in Spain and Portugal.

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 against the disease. These vaccines render pathogens harmless, vastly reducing their ability to infect a host. However the current version is considered unsafe, due to the possibility of the virus becoming infectious again due to mutations in the vaccine strains, causing African Horse Sickness in the host animal.

In 2016, the school-led research team developed a “reverse genetics” system that enabled strains to mimic viruses, demonstrating the 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 the virus and a successful mouse model displayed the potential for vaccine development.

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

As found in the mouse model study, 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.

There has never been an outbreak of African Horse Sickness in Britain but higher rates of midge dispersal in European countries, including the United Kingdom, increases the risk of a potential outbreak. This could have significant consequences for Britain’s horse industry, which contributes an estimated £7 billion to the nation’s economy.

“The high volume of movement in the horse industry increases the risk of the introduction of exotic diseases such as African Horse Sickness,” said the study’s principal investigator, Polly Roy, who is professor of virology at the London School of Hygiene & Tropical Medicine.

“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.”

She continued: “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 was hoped that the development of a safe and effective African Horse Sickness Virus vaccine can afford protection preventing any major impact in the event of an outbreak in European countries.

As the ECRA-developed vaccine does not require “live” and infectious materials, the vaccine would not only be cost-efficient but it could also be rapidly manufactured.

The authors say further research is needed to determine the optimal dosage requirements and the longevity of the vaccine.

The study was founded by the Biotechnology and Biological Sciences Research Council.

Valeria Lulla, Andres Losada, Sylvie Lecollinet, Adeline Kerviel, Thomas Lilin, Corinne Sailleau, Cecile Beck, Stephan Zientara, Polly Roy. Protective efficacy of multivalent replication-abortive vaccine strains in horses against African horse sickness virus challenge. Vaccine. DOI: 10.1016/j.vaccine.2017.06.023

The study, published under a Creative Commons License, can be read here


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