Published April, 2011

Since early February, the University of Kentucky Veterinary Diagnostic Laboratory (UKVDL) has been receiving reports from veterinarians who have seen large numbers of horses (mostly Saddlebreds) with oral lesions. The lesions have sometimes been described as nodules, vesicles, ulcers, and erosions on lips, gingival tongue, and buccal mucosa (the inner lining of the cheeks and lips). In some barns all animals are reportedly affected.

In one case the veterinarian stated that within 36 hours, the condition had spread to 18 horses in one barn. Another case report stated that none of the horses had lesions on the tongue, but all had gingival mucosa and gum-line lesions. Veterinarians have reported no fever or lethargy in affected horses. All animals apparently fully recover within a week or so.

On March 18 UKVDL received a similar report by a veterinarian who stated he saw these lesions (including lesions on the tongue) in horses on about four farms. He also said he had heard reports of similar cases across the United States this year.

Diagnostic Testing to Date

To date, testing for vesicular stomatitis (sporadically occurring virus that causes blisterlike lesions in the mouth and on the dental pad, tongue, lips, nostrils, hooves, prepuce, and teats of livestock) has been conducted on some animals, all with negative results. One biopsy of an oral lesion was submitted to UKVDL but was too small for researchers to perform a meaningful histopathological exam. Virus isolation was attempted more than once with no viruses isolated. Unfortunately, the lesions sampled were chronic in nature, which minimizes researchers' ability to pull out viruses. Samples of hay being fed also was examined for grass types; Researchers identified dallisgrass, crabgrass, purpletop, Johnsongrass, and yellow foxtail.

Differential Diagnoses (not necessarily in order of likelihood)

1. Unknown infectious agent
2. Trauma by plant awns/foreign bodies in hay
3. Chemical or other irritants in feed/hay/tack/buckets/water/other fluids in the environment
4. Vesicular stomatitis

Request from UKVDL

If you see any cases similar to what is described here in any species (regardless of whether you will be sending specimens to the lab), please report them to Deb Williams, Section Chief, Diagnostic Services, UKVDL at 859/257-7112 or dwillia@uky.edu, or Jackie Smith, Section Chief, Epidemiology, Jacqueline.Smith2@uky.edu.

The UKVDL recommends veterinarians working up an equine oral lesion case for a client follow this procedure to help the lab do its job:

• Take digital pictures of the lesions and send them to dwillia@uky.edu.
• If there are intact vesicles, aspirate fluid from at least three and place in a Red Top tube.
• Take at least three punch biopsies 4-6 mm in diameter (about ¼ inch) of the most acute-looking oral lesions (vesicles, nodules, erosions). If a biopsy is not possible, swab the lesions and place the swab in viral transport media or use a swab that has a breakable fluid contained receptacle or break the tip of the swab off into a Red Top tube with 1-2 mL normal saline to keep the swab moist.
• Draw blood and place 5 mL in EDTA (ethylenediaminetetraacetate) tube and 5 mL in Red Top tube.
• Send batches of hay being fed (minimum 2 lb per sample) and samples of supplemental feed (1 lb each) in plastic garbage bags or other suitable containers.

The more acute the lesions/fluids, the better the lab's chances of generating useful information.