Gluck Center Study on Equine Proliferative Enteropathy

While equine proliferative enteropathy (EPE) is most commonly seen during the fall (October) and early winter (January), a recent study at the University of Kentucky Gluck Equine Research Center by David Horohov, PhD, William Robert Mills chair and professor at the Gluck Center, and Allen Page, DVM, a doctoral student and Morris Animal Foundation/Pfizer Animal Health fellow at the Gluck Center, revealed that in Central Kentucky, exposure to the disease's causative bacterium can continue into March.

Equine proliferative enteropathy is an emerging equine disease that has been reported worldwide. The disease is caused by Lawsonia intracellularis, an obligate, intracellular, Gram-negative bacterium that invades intestinal crypt cells, primarily in the small intestine, and causes thickening of the intestinal lining. This thickening leads to clinical signs such as anorexia, weight loss, fever, lethargy, depression, peripheral/ventral edema (fluid swelling), and sometimes colic and diarrhea. A thickened small intestinal wall observed by a veterinarian via abdominal ultrasound is highly suggestive of EPE. Clinical EPE is typically found in weanlings and young yearlings, with only a few reports of older horses being affected.

Lawsonia intracellularis infections have been reported in a number of species, including pigs and laboratory animals, but not humans. The disease is significant not just because of its clinical aspects, but also because of its economic impact. A 2008 study by Michele Frazer, DVM, of Hagyard Equine Medical Institute, found that previously affected horses offered for public auction sold for 68% less than unaffected horses by the same sire.

The disease can be a frustrating problem for farms to deal with given the lack of definitive diagnostic tests, the sporadic occurrence of cases, and the unknown epidemiology of EPE.

Diagnosis of EPE revolves around clinical signs, ultrasonographic findings, and evidence of low total protein and albumin (a type of protein in the circulation), as well as results from commercially available diagnostic tests. Detecting low albumin (hypoalbuminemia) might be one of the most effective, rapid, and inexpensive tests for EPE in horses with other compatible clinical signs. Commercially-available tests include fecal polymerase chain reaction (PCR) and serum serology, although definitive EPE diagnosis can only be made after necropsy and relies upon detecting the organism in intestinal lesions.

Most horses with EPE respond well to antimicrobial therapy once diagnosed and treated appropriately, though some horses will ultimately die despite aggressive antimicrobial treatment. Due to the intracellular nature of L. intracellularis, most practitioners' antibiotic of choice is a tetracycline-class drug such as oxytetracycline or doxycycline. Some horses will also require supportive therapy, including plasma or fluids, to help support their circulatory system.

Though the epidemiology of EPE is uncertain, researchers believe transmission occurs when horses ingest L. intracellularis-contaminated fecal material from wild or domestic animals. Unfortunately, preventive measures for EPE are also poorly defined. While there is interest in developing a vaccine to prevent this disease, little is known regarding horses' immune response to L. intracellularis.

Recent research has added several important pieces to the EPE puzzle; however, a large amount of work is needed before this perplexing disease can be fully understood and prevented.

Allen Page, DVM, a doctoral student and Morris Animal Foundation/Pfizer Animal Health fellow at the Gluck Equine Research Center, provided this information.

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