The bacterium Lawsonia intracellularis causes an economically important emerging disease of weanlings called equine proliferative enteropathy (EPE). Thoroughbred foals that recover from EPE reportedly sell for an average of 68% less than nonaffected foals by the same sire, so veterinarians consider detecting the disease agent early a priority. In a recent study researchers recently examined four types of blood serum tests to determine their usefulness in detecting L.intracellularis, and the lead author presented their results at the 2012 American Association of Equine Practitioners' Convention, held Dec. 1-5 in Anaheim, Calif.

Although L. intracellularis has long been considered a common disease agent of swine, veterinarians began detecting its presence in horses about 20 years ago. Equine outbreaks occur sporadically and worldwide, but EPE is considered endemic on some farms that detect cases year after year. Historically, veterinarians based EPE definitive diagnoses on post-mortem test results because clinical signs of the disease could represent any number of diseases. But researchers have become more interested in developing effective serologic EPE diagnostic tests. Successful treatment, after all, depends on early diagnosis.

Connie Gebhart, PhD, associate professor in the University of Minnesota's Department of Veterinary and Biomedical Sciences at the University of Minnesota, and her colleagues collected blood serum samples from 96 weanlings in which they suspected EPE, 117 clinically normal weanlings, and 116 normal horses aged 1-27 years. They tested the samples using three assays: an immunoperoxidase monolayer assay (IPMA, commonly used to test swine for EPE), a slide-based immunoperoxidase assay (SIPA), and an enzyme-linked immunosorbent assay (ELISA).

The IPMA requires a special microscope and individuals trained in and experienced with this type of sample analysis. Personnel can read the SIPA using a standard microscope, and they read an ELISA by comparing color changes in a multi-welled plate