"Whisper Syndrome" Update

A treating veterinarian in southwestern Virginia still isn't sure what made three of his clients' horses sick this spring while generating widespread concern on an Internet message board. Titer results searching for a definitive diagnosis or rule-out on the bacterial disease listeriosis came back inconclusive in late May. But Thach Winslow, DVM, of Blacksburg, Va., the practitioner that treated the horses, says listeriosis cannot be ruled out as a differential diagnosis in the cases.

The owner of the affected animals, John Holland, had dubbed the illness in question "Whisper Syndrome," after he lost a horse by that name following rapid onset of inappetence, neurologic signs, and colitis. Necropsy results on the horse were inconclusive. Hundreds of horse owners signed onto a message board Holland devoted to the topic in March with concerns there might be a new disease affecting horses. Winslow and other veterinarians responded to the concerns saying that they didn't think a new disease or any sort of epidemic was taking place, but that owners should keep an eye on their horses for signs of illness. For background information, see www.TheHorse.com/ViewArticle.aspx?id=5584 and www.TheHorse.com/ViewArticle.aspx?id=5588.

Blood titers were run on samples from four horses on the premises taken while the cases were resolving and several weeks after the horses were better. Winslow also had comparative titers run on another horse that wasn't on the premise (thus serving as a control). Titer results are only run to a certain dilution, and up to the cutoff dilution level, the animals had similar titer results for listeria. The samples were re-run at higher dilutions, and the results were suspiciously high for the three horses exposed to round bales. These titers however, are not conclusive, but do help to build a case for listeria. Winslow explained, "The results could be circumstantial…they were certainly not conclusive that listeria is involved, but there was certainly enough evidence there to keep it on the suspicious list.

"There probably will never be a true diagnosis on those horses," he added. "However, it definitely raises an eyebrow enough that similar cases in the future should probably be considered listeria as a differential to rule out, hopefully by brain culture." He said veterinarians wouldn't be able to know more unless other cases turn up that seem similar enough for pursuing listeria diagnostics.

It was suggested on the message board that the sick horses might have become sick from eating round hay bales. Winslow emphasizes that the bales were only suspect. "My recommendations for feeding round bales have not changed at all since this occurrence, in that feeding round bales is an acceptable practice, but I encourage round bales to be high-quality hay. Often times, farmers choose to round bale their lower quality hay. If you choose to use round bales, be careful in selecting them.

"The hay should be barn stored, and it should certainly be fed free choice, and that means don't make them clean up all the scraps--that's the stuff that tends to get moldy. If they start to get to the end of one, it's time to start on another. Even with those recommendations, because you're taking a large amount of feed and exposing it to environmental conditions for a long period of time, there could still be some risks."

Since the cases haven't been confirmed as anything specific, Winslow doesn't want to "paint the picture too hard." However, if the cases are the same illness, he notes depression, unexplained dysphagia (difficulty swallowing), an inflammatory CBC (complete blood count, as indicated by a high white blood cell count) were the most notable signs he saw. "The depression and inflammatory CBC--you can see that with a lot of diseases," he explained, but the dysphagia and the fact that the horses were afebrile (they had no fever), seemed unique.

"If people take the right approach to be aware, but not paranoid, we might help a few horses or come up with an actual diagnosis one of these days," he added.

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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