Prevalence of L.intracellularis on Farms (AAEP 2011)

If someone had said "equine proliferative enteropathy" 10 years ago, chances are most horse breeders would have shrugged their shoulders and paid little mind. Today, however, many breeders are mindful of this still-emerging young horse disease caused by the Lawsonia intracellularis bacteria. Researchers have made great strides in comprehending many facets of the disease. Recently, a team from the University of Kentucky, using a newly developed assay, took several steps forward in understanding L. intracellularis' environmental prevalence on certain horse farms compared to its seroprevalence (presence of positive serum antibodies) in horses residing on those farms. Allen Page, DVM, a PhD candidate at the University of Kentucky’s Gluck Equine Research Center, presented the findings during a presentation at the 2011 American Association of Equine Practitioners convention, held Nov. 18-22 in San Antonio, Texas.

Equine proliferative enteropathy (EPE) has been reported worldwide and is gaining prevalence in the United States. L. intracellularis 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, reduced daily weight gain, fever, lethargy, depression, peripheral/ventral edema (fluid swelling), and sometimes colic and diarrhea. Reduced daily weight gain and weight loss can be a costly problem for many Thoroughbred breeders, as smaller foals tend to bring lower prices at auction. The current lack of definitive diagnostic tests is another frustration for breeders and veterinarians alike.

Recently, Page and a team of researchers developed a modified enzyme-linked immunosorbent assay (ELISA) test that detects antibodies to L. intracellularis—the first serologic assay able to detect the antibodies and, thus, L. intracellularis exposure. Using this test, the team evaluated the seroprevalence of L. intracellularis among 337 Thoroughbred foals and weanlings residing on 25 Central Kentucky farms.

"Case information from the three years preceding the study was used to classify farms as having no prior recent history of EPE, a suspected history of EPE, or a confirmed history of EPE," he explained. Then, from August 2010 to January or February 2011 (the study officially ended in January, but some farms opted to have foals tested in February as well), the research team collected monthly serum samples from the aforementioned foals, testing them for L. intracellularis-specific antibodies.

Upon reviewing the findings, Page and his colleagues found an overall seroprevalence of 68%, with seroprevalence levels on individual farms ranging from 14-100%. Page was quick to point out that the overall seroprevalence of 68% isn’t likely representative of the Central Kentucky Thoroughbred population, due to the large number of previously affected farms included in the study. Other key findings included:

  • All farm populations had evidence of L. intracellularis exposure, regardless of whether they had logged previous cases of EPE;
  • On average, the L. intracellularis seroprevalence was significantly lower on farms with no history of EPE cases than on those with confirmed or suspected EPE cases; and
  • Horses residing on farms with no history of EPE cases tended to have lower L. intracellularis antibody levels.

"Using an ELISA to detect serum antibodies to L. intracellularis from young horses on numerous farms, seroprevalences corresponded well with past history of EPE cases," Page concluded. "The data presented here suggests that lower environmental burdens of L. intracellularis result in fewer horses being exposed to the bacterium and less antigenic stimulation (promoting an immune response) per exposure."

The findings in the study correlated well with EPE diagnoses made by local veterinarians, Page added.

With the development of the first serologic test to identify the presence of L. intracellularis antibodies, Page et al. have found a way to measure exposure to the causative bacteria. His study also revealed that while all farms included had evidence of L. intracellularis in the environment, the seroprevalence of the bacteria in horses residing on those farms ranged from 14-100%. Further research is needed to find a possible explanation for the farm-to-farm difference in L. intracellularis seroprevalence.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.

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