Infection with Lawsonia intracellularis (most often seen in weanlings) can cause edema (fluid swelling) beneath the abdomen and in the lower limbs, lethargy, anorexia, diarrhea, fever, colic, and weight loss. It is a "true emerging disease with more cases every year," according to Nicola Pusterla, DVM, Dipl. ACVIM, associate professor of veterinary medicine and epidemiology at the University of California, Davis.

At the 2008 American Association of Equine Practitioners convention, held Dec. 6-10 in San Diego, Calif., Pusterla discussed the effectiveness of three vaccination strategies against L. intracellularis, which causes proliferative enteropathy (a spreading intestinal disease). "Although the clinical entity (L. intracellularis infection), diagnostic evaluation, and treatment of affected foals have been well-established and described, preventive measures have remained largely unaddressed," he noted.

Pusterla et al. investigated the immune response and fecal shedding of L. intracellularis following two doses of a modified-live vaccine (Enterisol Ileitis from Boehringer Ingelheim Vetmedica) given orally or intrarectally three weeks apart. Fifteen healthy, L. intracellularis-negative foals were divided into three groups of five, with one foal in each group remaining unvaccinated as a sentinel.

Group 1: Vaccinated orally without premedication.

Group 2: Vaccinated orally following premedication with a proton-pump inhibitor to reduce stomach acidity (omeprazole, GastroGard).

Group 3: Vaccinated intrarectally.

The researchers reported the following:

  • Intrarectal administration of vaccine induced seroconversion (production of detectable antibodies) in all foals after only one dose, while only two foals in Group 2 and zero Group 1 foals seroconverted after one dose.
  • Both oral vaccine groups had one nonresponder (no detectable seroconversion).
  • Fecal shedding of L. intracellularis occurred mostly in Group 3 foals up to 15 days after the first dose.
  • GastroGard premedication appeared to help the vaccine induce a stronger, earlier antibody response when given orally.
  • No adverse reactions were noted in any foals.
  • No sentinel (unvaccinated) foals seroconverted, indicating no exposure to virulent L. intracellularis.

"We are in the process of refining the vaccination protocol and working with lower doses and different vaccine preparations (two forms are on the market)," said Pusterla. Challenge studies and field efficacy trials to determine protection with the vaccine are in the works.

About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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