TESTS FOR SPECIFIC DISEASES

A number of tests are available to determine whether a horse has been exposed to particular organisms that cause diseases. “The disease bloodwork falls into two categories,” says Wilson. “One is testing for antibodies against that disease, produced by the animal after being exposed to that disease. The other category is tests that look for the organism itself. By far the majority of tests are simply testing to see if antibodies are there.”

Sometimes, a veterinarian might run more than one type of test to confirm a result. “Many disease processes have multiple types of tests available to help diagnose them, and new literature is constantly being published as to which methods are most reliable,” Arbittier says. The options include:

• Enzyme-linked immunosorbent assay (ELISA). The ELISA test consists

of a plastic plate with columns of wells that come from the manufacturer coated with a reactive substance, usually an antigen0. When fluid samples from the horse are placed in the wells, any antibodies present will bind with the antigens. Then, the wells are emptied and refilled with other solutions that will bind to any antibodies present to produce a color change that will be visible to the naked eye. The result is an on/ off positive or negative. However, false positives are possible, and a light color change might be an inconclusive result.

ELISA tests can also be used to measure a horse’s hormone levels, such as insulin or adrenocorticotropic hormone (ACTH), to look for metabolic diseases. “Leptin [a hormone produced by fat cells] is another thing the lab can look for. Some are offering this as an insulin resistance panel when checking for equine metabolic syndrome,” True says.

• Western blot or immunoblotting. Like ELISA, Western blotting works by

providing antigens to bind to antibodies in a horse’s blood in a way that can be seen. The biggest difference is that the Western blots first separate the proteins in the horse’s blood into bands on a sheet of gel so that veterinarians can see exactly which ones are causing the reactions. This offers more specificity than the ELISA.

• Indirect immunofluorescent antibody technique (IFAT or IFA). IFAT is another, newer method that utilizes the antigen-antibody bond to produce a visible result. In this test, fresh or frozen tissue samples are bathed in solutions that contain antibodies combined with fluorescent dyes, which then bind with any antigen proteins on the surface of the cells. The fluorescent dyes can then be visualized by any of several imaging techniques. Both IFAT and ELISA are used to test horses for antibodies to equine0 protozoal myeloencephalitis (EPM).

The downside of all of these tests