Lawsonia Infections: An Emerging Problem

Over the past decade, Lawsonia intracellularis, the bacterium responsible for proliferative enteropathy (a spreading disease of the intestines), has been diagnosed with increasing frequency in horses and is now a significant problem in the industry.

L. intracellularis infections cause diarrhea, depression, fever, inappetance (anorexia), weight loss, edema (fluid swelling) on the abdomen or lower limbs, a poor hair coat, and intermittent colic due to thickening of mucosal lining in the small and large intestine. While any age of horse can be infected, weanling foals 4 to 7 months old are most susceptible.

According to Jean-Pierre Lavoie, DMV, professor of Equine Internal Medicine at the University of Montreal in Canada, a surge in the number of cases of L. intracellularis has been noted in various geographical locations.

"Equine cases of proliferative enteropathy have been reported in the North America, Great Britain, and Australia," reported Lavoie. "While most cases are isolated (one or two animals per farm), outbreaks have occurred."

An increase in the number of L. intracellularis cases in Central Kentucky has also been identified, as previously reported by The Horse (articles #8184 and #9869).

Henry Staempfli, VetMB, Dipl. ACVIM, professor Large Animal Medicine at the Ontario Veterinary College, in Canada, said that L. intracellularis seems to be an emerging problem.

"Ontario has also seen a surge in the number of cases," said Staempfli. "While L. intracellularis rarely causes death, this is a costly disease to treat and can often go unrecognized for weeks in individual cases, causing weight loss and very low blood protein concentrations."

Two tests are currently available for L. intracellularis: a fecal PCR (bacterial DNA-based test) and a blood enzyme-linked test (that measures antibody concentrations). Samples can be obtained on the farm by the primary veterinarian and rapidly analyzed by a qualified laboratory.

Once diagnosed, affected animals can either be treated as outpatients or at an equine referral hospital.

"Antimicrobials such as erythromycin (alone or combined with rifampin) or tetracycline are usually sufficient in mild cases. More severe cases typically require plasma transfusions, anti-ulcer medication, intravenous fluid therapy, and rarely, parenteral (IV) feeding," explained Lavoie.

According to Staempfli, "The source of bacteria and mode of transmission are unknown, and it remains unclear why some foals are affected and not others. The disease is well-studied in pigs and is commonly seen in best health managed pig farms all over the world. Research needs to focus on identifying carriers and reservoirs of L. intracellularis on horse farms."

A live vaccine has recently become available for pigs. No vaccine is currently available for horses.

About the Author

Stacey Oke, DVM, MSc

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she's worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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