WWI-Era Bacteria: The Key to Eradicating Strangles?

WWI-Era Bacteria: The Key to Eradicating Strangles?

The current S. equi strain didn’t appear until around the time of World War I, during which horses (like this one, pictured in Switzerland in 1917) played major roles both in the battles and behind the scenes.

Photo: Courtesy of the Swiss Federal Archives/Wikimedia Commons

In the war against strangles, researchers believe they've discovered a critical genomic influence: war.

Although veterinarians have been diagnosing strangles since the 13th century, the current strain of the causative agent didn’t appear until the early 20th century. Specifically, it was around the time of World War I.

Hoping to create a vaccine that would ward off all existing variants of Streptococcus equi (S. equi), the bacteria that causes strangles, British researchers started mapping bacterial genomes. They investigated the DNA of 224 S. equi samples from around the world to find a common genomic ancestor to this approximately 800-year-old agent. But to their surprise, the samples were very closely related. And they all appeared to have been derived from common ancestors dating back only about 100 years.

S. equi has been infecting horses for many hundreds of years, but it appears that the older strains have died out, being replaced by what we see today,” said Andrew Waller, BSc, PhD, from the Animal Health Trust, in Newmarket, U.K.

“We went into the historical aspect of the study thinking that S. equi would date back much further,” he added.

It didn’t, however. The war claimed the lives of many men, many horses, and many bacteria, apparently. As the older horses died or were killed, their strains of S. equi went with them. Then, in an effort to quickly rebuild the beaten-down equine population, European studs led intensive breeding efforts, producing thousands of young horses and, inadvertently, plenty of “naive blood” for the newest mutated forms of S. equi to exploit.

And exploit they did, as strangles continues to be the most frequently diagnosed infectious disease of horses worldwide, Waller said. With more than 600 new outbreaks every year in the U.K. alone, its success is probably due to its ability to “hide” in small pus pockets in affected horses’ heads long after they appear to recover from the glandular swelling and fever typical of strangles.

Through their efforts, Waller and his fellow researchers might well be on the road to developing a potent vaccine that, based on this World War I-era ancestor, could target all current strains of the bacteria.

“The data we have gathered in this study has enabled us to pinpoint the genes that help the bacteria to persist, spread, and thrive in the horse population,” Waller said. “This research provides an unprecedented opportunity to exploit this information toward preventing strangles in future generations of horses.

“Current diagnostic tests are very useful as screening to help prevent strangles outbreaks,” he said. “But a new vaccine could finally swing the tide toward the eradication of this disease.

“We are absolutely committed to helping to develop new vaccines against strangles, which could maintain the health of horses even if they were inadvertently exposed to S. equi during attendance at sales or events,” Waller told The Horse.

Until that vaccine has been developed, however, horse owners can take advantage of advice from experts on reducing the risk of strangles, Waller added. Guidelines provided by the Horserace Betting Levy Board Code of Practice and the British Horse Society could “help owners to avoid future outbreaks and keep their horses healthy,” he said.

The study, “Genome specialization and decay of the strangles pathogen, Streptococcus equi, is driven by persistent infection,” was published in Genome Research

About the Author

Christa Lesté-Lasserre, MA

Christa Lesté-Lasserre is a freelance writer based in France. A native of Dallas, Texas, Lesté-Lasserre grew up riding Quarter Horses, Appaloosas, and Shetland Ponies. She holds a master’s degree in English, specializing in creative writing, from the University of Mississippi in Oxford and earned a bachelor's in journalism and creative writing with a minor in sciences from Baylor University in Waco, Texas. She currently keeps her two Trakehners at home near Paris. Follow Lesté-Lasserre on Twitter @christalestelas.

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