A Blood Test to Detect Equine IAD?

Inflammatory airway disease (IAD) in horses, which has been historically difficult to diagnose, might soon be easily detected via a simple blood test, according to a French equine respiratory specialist.

"The results of our present study indicate that IAD is associated with a detectable, albeit moderate, increase in circulating rates of surfactant protein D (SP-D) in the blood," said Eric Richard, DVM, MSc, PhD, researcher at the Frank Duncombe Laboratory in France, at the 2012 French Equine Research Day held March 1 in Paris. Richard relayed that SP-D plays a principle role in immunity in the alveoli--the thousands of small balloonlike structures within the lungs that participate in the exchange of gases used in breathing.

Inflammatory airway disease can cause poor performance and exercise intolerance in horses, and it is occasionally associated with a slight cough at rest, said Richard. As it is generally not an infectious disease, laboratory testing of blood samples cannot provide clear links to the condition. The most effective evaluation method currently available is an examination of the cells of the lungs using a bronchoalveolar lavage (BAL), an invasive and expensive procedure requiring sedation, Richard noted.

In his preliminary study, Richard and his colleagues tested the blood serum of 20 healthy horses and 22 horses previously diagnosed with IAD, before and after 60 minutes of treadmill exercise. The IAD horses had significantly higher amounts of SP-D in the blood compared to the healthy horses, both before and after exercise. However, there was no significant difference in the amount of SP-D before and after exercise within each of the two groups. In other words, exercise did not seem to affect the amount of circulating SP-D, whether in healthy horses or those with IAD.

The increase in SP-D in the blood suggests that the alveoli have been damaged, according to Richard. This damage actually makes the alveoli more permeable (meaning that the gas exchange is not as well controlled) as a result of the inflammation.

"This is consistent with the information we have about SP-D in humans with inflammatory respiratory disease," Richard said. "Even so, it's possible that exercise could affect the SP-D rate and that that difference is only detectable a few hours later."

The study--which was made possible by the 2010 French Veterinary Equine Research award and appeared in the Equine Veterinary Journal--also gave Richard reason to believe that improved diagnostic procedures could help practitioners zone in on more specific subtypes of IAD.

"I'm convinced that in a few years we will no longer talk about IAD but about several types of IAD," he said.

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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