Adaptation and validation of a bacteria-specific enzyme-linked immunosorbent assay for determination of farm-specific Lawsonia intracellularis seroprevalence in central Kentucky Thoroughbreds.

REASONS FOR PERFORMING STUDY: Lawsonia intracellularis is the causative agent of equine proliferative enteropathy (EPE), a disease for which no large-scale seroprevalence studies have been conducted.

OBJECTIVES

To validate and use an equine-specific enzyme-linked immunosorbent assay (ELISA) for L. intracellularis to determine the seroprevalence of L. intracellularis on numerous farms.

METHODS

An ELISA, in which purified antigen was used, was adapted from previous work in swine. A total of 337 Thoroughbreds from 25 central Kentucky farms were enrolled and monthly serum samples collected from August 2010 to January/February 2011. Samples were screened for L. intracellularis-specific antibodies using a modified ELISA. Farms were classified into one of 3 groups based on 3 year prior history with EPE.

RESULTS

The ELISA intra-assay coefficient of variation (CV) was 6.73 and inter-assay CV was 9.60. An overall seroprevalence of 68% was obtained, with farm-specific seroprevalances ranging from 14 to 100%. A significant difference was found in the average seroprevalence (P<0.05) on farms with a confirmed recent history of EPE cases. Additionally, both lower average ELISA unit (EU) values (P = 0.079) and maximum EU values (P = 0.056) were detected on farms with no recent EPE history when compared to the other groups. A bimodal exposure distribution to L. intracellularis was detected in the fall and winter months.

CONCLUSIONS

Recent history of EPE was associated with higher average seroprevalence indicating increased exposure on farms with prior cases of EPE. Seasonally bimodal exposure was also observed.

POTENTIAL RELEVANCE: The adapted ELISA appears to be useful for determination of L. intracellularis-specific antibody levels. The high farm-specific seroprevalences and bimodal distribution of exposure to L. intracellularis were unexpected and suggest that farms with a previous history of EPE remain at risk due to heightened exposure levels beyond early winter.