Researchers Digging Deeper into African Horse Sickness

Researchers Digging Deeper into African Horse Sickness

African horse sickness, a fatal viral disease spread by Culicoides, has a 75-90% mortality rate in horses.

Photo: Manuel Rodriguez

As the threat of African horse sickness (AHS) in parts of Europe grows, scientists are turning to a genetic level of understanding and fighting the disease.

African horse sickness is a fatal viral disease spread by Culicoides--tiny, blood-sucking insects--that can affect horses, mules, and donkeys, as well as dogs and camels. Horses are most susceptible to AHS, with a 75-90% mortality rate. A vaccine is available, but no effective treatment methods exist for infected horses. For survivors, recovery is slow.

Researchers at the London School of Hygiene and Tropical Medicine, in England, have recovered the AHS-causing virus from RNA (a special kind of genetic material involved in gene expression) they developed in their own laboratory. With that synthetic material, the researchers hope to use what they call “reverse genetics” to comprehend the virus at the molecular level—how it reproduces and spreads, how it interacts with the infected animal’s cells, and how it causes disease. But perhaps more importantly, their work can contribute to vaccine development, said Polly Roy, MSc, PhD, FMedSci, professor of virology and supervising researcher on the project.

“This kind of vaccine is very different in its mechanism of action compared to a traditional rabies or flu vaccine, because those are based on recombinant (or those developed in a laboratory) proteins, not on the actual virus,” Roy said.

In reverse genetics, researchers study what happens when they modify certain genes or parts of genes. Conversely, in “regular” genetic studies, scientists investigate the opposite: They usually try to understand what a certain gene or part of a gene does or what its role is. By reversing the process—seeing how their genetic manipulations result in changes—Roy and colleagues are hoping to better understand how they can control this deadly virus.

Roy’s team—with primary researcher Yuuki Kaname, PhD—created a synthetic version of the RNA by cloning RNA sequences from AHS viruses in their laboratory. With cloned synthetic RNA, researchers have nearly limitless opportunities to experiment with modifications that could make the virus powerless, Roy said. When developed into a vaccine, the modified synthetic RNA could protect horses from developing the disease, if infected, by disarming the incoming virus.

Reverse genetics vaccines have already been successful in reducing the spread of the “avian influenza” (H5N1) virus. They have also been developed for the bluetongue virus, which is similar to AHS but affects primarily sheep instead of horses. Both the bluetongue and AHS viruses are transmitted via a biting midge. However, the bluetongue virus is genetically quite different from the AHS virus, making the development of the AHS vaccine a separate—and long—process.

“A virus-based vaccine using a reverse genetic system takes considerable time to develop,” Roy said.

But even if the scientists progress rapidly in their vaccine development process for AHS, it will likely be several more years before the vaccine is actually available, said Roy: “We do not have the company yet who can take it to market. This takes time, and a delivery date cannot be predicted.”

The study, "Recovery of African horse sickness virus from synthetic RNA," was published in The Journal of General Virology

About the Author

Christa Lesté-Lasserre, MA



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