How does bacteria cause strep throat, and how can we prevent it? The answer may lie in the genes, and now scientists are one step closer to finding that answer. And they couldn’t have done it without horses.

Horses and humans get similar throat infections via genetically similar bacteria. While humans get Streptococcus pyogenes, which causes “strep throat,” horses get Streptococcus equi, which causes “strangles.” Human strep researchers were hoping to figure out what it was in the S. pyogenes genome that made it able to infect human saliva, and they got some help from veterinary scientists overseas.

A horse peers over a fence in Danville, California. Kristin Hugo / Strange Biology

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Researchers at a veterinary and research charity in the UK called Animal Health Trust found a way to test all of the equine strep genes simultaneously. The people studying human strep at Houston Methodist Research Institute in Texas, on the other hand, were worried that they’d have to test each strep gene one at a time. That’s when their veterinary friends reached out and showed them the more efficient route of gene analysis.

After sharing the technique with American strep researchers, they were able to analyze all the genes of human strep and quickly identify which ones allowed the bacteria to grow in human saliva. They successfully identified 92 genes that helped human strep grow in the lab, and follow-up tests confirmed that six genes affected their growth in human saliva.

Streptococcus pyogenes is more than just a seasonal bother. The Center for Disease Control and Prevention estimates that invasive Group A strep infections affect 11,000 to 13,000 Americans each year, and noninvasive infections, like strep throat, are thought to infect millions. Invasive infections have a fairly high mortality rate for a bacteria, of nearly 14 percent.

The equine bacteria causes similar symptoms in horses: trouble swallowing, yellow discharge from the nose, coughing, swelling and abscesses, high temperatures, and loss of appetite. It’s highly contagious and sometimes fatal for our trusty mounts.

The equine vets had been studying strangles for years, analyzing the genes of the bacteria to identify which genes help it survive in different conditions. They developed the new gene analyzing tool so that one day they might develop a vaccine to prevent horses from getting the sickness. Understanding the genes that affect human strep is the first step to developing a vaccine for us, too.