Genome Blueprint for Horse and Human Vaccines

Two strains of Streptococcus bacteria that have evolved to cause potentially fatal infections in either horses or humans share similar disease-causing mechanisms. Exploiting their genetic similarities could lead to novel vaccines for both man and animal, according to a review published in the Journal of Medical Microbiology.

Gluck Equine Research Center's John Timoney, MVB, MRCVS, MS, PhD, co-authored the paper entitled, "Streptococcus equi: a pathogen restricted to one host." Andrew Waller, PhD, was the lead author, and Romain Paillot, PhD, was the other co-author. Both work with the Animal Health Trust's Centre for Preventative Medicine in Newmarket, Suffolk, United Kingdom.

Streptococcus pyogenes is responsible for tonsillitis, scarlet fever, and toxic shock syndrome in humans. Its equine equivalent, Streptococcus equi, infects horses, causing a disease called strangles. Each strain is well adapted to its particular host, yet their strategies for causing disease are remarkably similar.

Strangles is one of the most frequently diagnosed equine infectious diseases worldwide and costs thousands of dollars per horse to resolve. Streptococcus equi infects the lymph nodes in the head and the neck, leading to abscesses that can restrict the airways-giving the disease its name.

The secret to S. equi's success is its ability to trade genes with similar bacteria such as S. pyogenes, explained Waller.

"These strains share clever tricks, like secreting 'super antigens' that allow the microbes to send the immune system into turmoil yet avoid detection themselves," he said.

Another shared trait is the production of SlaA-a toxin related to Australian brown snake venom, which is associated with serious disease in humans.

"The resemblances between the two strains prove it is unrealistic to study human and animal pathogens in isolation, in our quest to understand and fight them," Waller said.

Data show that cases of serious, invasive S. pyogenes infection have increased in recent years in England.

"Tracking the genetic evolution of micro-organisms such as S. equi will give us clues as to how its human counterpart, S. pyogenes, has evolved in the past and may evolve in the future," Waller said. "This will help equip us with the tools to combat the diseases caused by both pathogens."

Researchers are using the emerging genetic data of S. equi as a blueprint to develop a new vaccine against strangles, which ultimately could benefit both horses and humans.

"One vaccine against strangles that is currently being trialed uses antigenic components that share similarity with their S. pyogenes counterparts to stimulate immunity," Waller said. "If this approach can protect horses against S. equi, it is feasible that a similar cocktail of S. pyogenes antigens may be the basis for an effective vaccine for humans, which is an exciting prospect."

Edited press release from the Society for General Microbiology.

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