Diagnosis of EIA

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Methods of testing:
Two test methods are currently employed for EIA testing:


1) Coggins Test

    This test was first developed by Dr. Leroy Coggins and is recognized as the “gold standard” for confirmation of EIA virus. The method employs a agar gel immunodiffusion test (AGID). In this method, test serum from a “potentially infected” horse and EIA virus antigen are placed in separate wells in a gel. If the test serum contains antibodies to EIAV, a visible precipitation line forms where the two reagents meet in the gel. Once infected with EIAV, a horse’s serum will contain antibodies against the virus for life whether clinically sick or not. This  tests for antibodies but cannot detect the virus itself.

2) ELISA 

    An enzyme-linked immnunosorbent assay (ELISA) method works by the binding of horse serum antibodies and EIAV antigen causing a color change in the reaction well. A positive ELISA test is then confirmed with repeat AGID tests.


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Virus Isolation

    Virus isolation is occasionally done by inoculating blood from a suspected carrier onto leukocyte cultures. Virus identity is then confirmed using ELISA or immunofluorescence test.

    Testing of horses moving across state and international borders does vary by country and state laws. Many jurisdictions require periodic tests, a single mandatory test, or test before entering organized events. In general, the AGID test method is required for horses moving internationally. An EIA ELISA test is acceptable for movement of horses into Canada.

    Newer testing methods are currently being looked at as a basis to increase levels of both sensitivity and specificity.  Further information can be obtained via:


USDA EIA fact sheet: http://www.aphis.usda.gov/lpa/pubs/fsheet_faq_notice/fs_aheia.html

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Differential Diagnosis:

    Differential diagnosis for EIAV are as follows:
       For the acute disease: Purpura hemorrhagica, Babesiosis, Equine granulocytic ehrlichiosis, Equine viral arteritis, Autoimmune hemolytic anemia, Leptospirosis, Parasitism and Idiopathic thrombocytopenia.

       For the chronic disease: Internal abscessation(metastatic Streptococcus equi infection), Chronic inflammatory disease, neoplasia and chronic hepatitis.

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