AAEP Convention 2005: Early Diagnosis of EPM with Biomarkers

A researcher has found a reliable way to diagnose equine protozoal myeloencephalitis (EPM) in the acutely affected horse by examining genetic markers in its blood. This technique could potentially be applied to detect evidence of other infectious diseases before clear clinical signs appear.

Martin Furr, DVM, Dipl. ACVIM, PhD, professor of internal medicine and chief of medicine at the Virginia-Maryland Regional College of Veterinary Medicine, presented information on his study examining the microarray gene chip analysis technique at the 2005 American Association of Equine Practitioners Convention, held Dec. 3-7 in Seattle, Wash.

"This method is a way to assess the expression of several genes all at one time," Furr explained. "It's a very new technique and sort of earth-shattering technology." He used a gene chip--a 1.2 cm-square membranous disk with a grid that has about 500,000 potential spots to place gene probes, which detect the expression of particular genes in the horse. There were around 3,000 probe sets on the type of chip he used. Each set probes the DNA in a blood sample for a particular gene's expression.

Theoretically, different diseases should have different patterns or "signatures" of expression. "The combination of genes and strength of signal represent the signature we're looking for in our sample," he said. "We will generate a database comprised of normal and diseased horses. When our diagnostic signature matches the diagnostic signature for one of our referenced diseases, then we have a confirmed diagnosis."

In the current study, Furr used 20 horses that were the control group of a separate EPM treatment study. He induced signs of EPM in this group with the stress transport model.
In these horses, he and his colleagues noticed that of the 3,000 genes they assayed, the expression of 23 genes in horses with clinical EPM disease was statistically different than the expression of those genes in horses without EPM. He examined these closer and found six gene markers that can determine if the horse has EPM or not.

"These had a very high sensitivity and specificity for disease vs. no disease," he said. "(Sensitivity and specificity) peaked through Days 17-24, with an overall efficacy of about 95-98% in classifying horses.

"In summary, we developed a diagnostic signature for EPM that proved to be highly accurate at least in the acute phase of infection, up to 28 days," he said. "This can be used for a diagnosis for this and other diseases. Ongoing studies are looking at the diagnostic efficiency of this technique in naturally occurring field cases--this is going more slowly than we'd hoped, so I can't give a timeline on when they will be ready. But hopefully, (the EPM test) will become commercially available in the future."

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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