Multiple Antigen Types for EPM
Pathogenes Inc. (Fairfield, Florida) is a company which has recently identified multiple antigen types for EPM. This is in contrast to our recent belief that only one antigen type (known as SAG 6) existed. Pathogenes' discovery carries great clinical significance because our medical approach has been historically directed at diagnosing and treating disease caused by the SAG 6 antigen type only.
In addition to SAG 6, Pathogenes has identified two other antigen types: SAG 1 and SAG 5. They have also developed Elisa tests for each one.
Horses testing negative for the SAG 6 antigen type (via the Western Blot method) were previously considered to be free of EPM infection. During this test, potential positive titers for one or more of the other antigen types (SAG 1 and/or SAG 5) would have gone undetected, thereby producing false negative results.
Moreover, horses which tested positive for the SAG 6 antigen type and did not respond to treatment (such as Marquis® administration) may have had concurrent infection with one or more of the other antigen types (which may not respond to Marquis®). In these cases, residual neurologic deficits were erroneously considered to be permanent and irreversible.
The current knowledge that multiple antigen types for EPM exist enables veterinarians to more accurately diagnose and more effectively treat this disease.
Pathogenes: Diagnosis of EPM
Pathogenes used experimental and confirmed cases of EPM to determine that SAG 1, 5, and 6 ELISA titers detect the organism shortly after the parasite enters the blood stream.
The disease, EPM, is a sequela of Sarcocystis neurona infection.
An advantage to the SAG ELISA test is the ability to determine therapy choice. The Peptide ELISA detects antibodies to the 3 antigen types of S. neurona and the test result is reported as a titer. These three titers indicate reaction to different proteins that identify the three antigenic types of S. neurona causing the infection. The total cost for the test (revealing all three Elisa titers) is $60.
Pathogenes found no advantage in using cerebral spinal fluid (CSF) to detect infections.
What Do the Results Mean?
Mixed infections are the most common situation.
Pathogenes does not have false positive results due to the specificity of the antigens although the presence of one cross-reactive phenotype can confound other testing.
Any titer (to any of the three antigens) that is less than 4 means the animal has no response to active parasites or it is too early in the infection (less than 15 days) to have a measurable response. If the titer is negative and the horse has a presumptive diagnosis of EPM a second titer should be obtained two weeks later.
Any titer to the three antigens that is greater than 4 means the animal has had experience with the parasite and may or may not have an active infection. Two tests, performed two to four weeks apart can determine if the infection is currently active. The titer should increase (2 to 4 fold) with progression of the disease or decrease with disease regression or elimination.
Titers at 16 or greater are supportive of active EPM infection.
The best use of the test is in conjunction with neurological examination. The test is indicated for cases in which the horse is exhibiting clinical signs consistent with neurologic disease that could be attributed to S. neurona infection. Screen testing in normal horses is rarely advised.
Pathogenes: Treatment of EPM
Horses do show ataxia and inflammatory responses to all three phenotypes of S. neurona. The best drug for treatment should be based on knowledge of the antigen type of the S. neurona causing the infection.
Pathogenes recommends treatment for EPM based on the 3 antigen titers reported.
A field trial using Oroquin-10, a 10-day drug treatment for EPM, is currently available. This non-toxic drug is absorbed quickly and kills intracellular pathogenic protozoa that can evade other treatments (which leads to relapse conditions). Oroquin-10 is non-toxic to animals and is formulated to stimulate protective immunity during treatment. The in vitro efficacy against SAG 1 and SAG 5 phenotypes has been established. Challenge trials are ongoing. The drug is safe in horses at 10 times the prescribed dose. No side effects have been reported. The cost of Oroquin-10 treatment is approximately $200.
In our experience, the testing and treatment protocols offered by Pathogenes are more accurate, effective, and economical than current strategies that use Western Blot titers for testing and treatment with medications such as Marquis®.
You can learn more about Pathogenes HERE. We encourage you to view the available Webinar for more information.