Emerging Pathogen Lawsonia Detailed in New Study

Lawsonia intracellularis is known to be the causative agent of proliferative enteropathy (a spreading disease involving the intestines) in horses and is an important emerging pathogen responsible for a number of North American outbreaks. But where the bacterium comes from, how it is spread, and how general equine practitioners can efficiently recognize the disease are questions that researchers are eagerly attempting to answer.

"L. intracellularis infects cells lining the inside of the small intestine, particularly the ileum, and causes these cells to expand and elongate," explained Michele Frazer, DVM, Dipl. ACVIM, an equine practitioner at Hagyard Equine Medical Institute in Lexington, Ky., and author of the study, "Lawsonia intracellularis infection in horses: 2005-2007."

Consequences associated with the proliferation of the small intestinal lining include loss of protein (e.g., albumin), malabsorption, poor body condition, weight loss, and diarrhea.

Frazer retrospectively reviewed medical records of 57 horses treated for L. intracellularis at Hagyard to describe factors associated with infection including age, sex, month of presentation, clinical signs, laboratory findings, and outcome to better characterize the disease.

"The goal was to better define L. intracellularis to assist equine practitioners more quickly diagnose disease and prevent future outbreaks," stated Frazer.

Frazer found that horses infected with L. intracellularis:

  • Were 2-8 months of age;
  • Presented between August and January;
  • Had ventral edema (81% of infected horses) and hypoalbuminemia (100%);
  • Do not necessarily test positive for L. intracellularis by fecal polymerase chain reaction (PCR) or a blood test (the serum immunoperoxidase monolayer assay);
  • Have good survival rates (93% of infected horses lived), and;
  • Are sold for 68% less money as yearlings than other yearlings that had no known history of infection.

Foals and weanlings presenting with the above-described signs should be considered potentially infected with L. intracellularis and appropriate tests (e.g., abdominal ultrasound of the ileum and small intestine, PCR, and serum tests) should be performed. Once a positive diagnosis has been achieved, appropriate therapy can include antibiotics, synthetic colloids, and/or plasma transfusions.

According to Frazer, "Ongoing research efforts are looking at improving diagnostic tests and identifying the source and transmission of the bacterium."

Frazer's study is scheduled to be published in an upcoming edition of the Journal of Veterinary Internal Medicine. The abstract is currently available on PubMed.

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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