Due to the persistence of EIAV in infected equidae, detection of EIAV antibodies confirms the infection. For this purpose, the p26 protein of the viral core is employed for diagnosis purposes.
To clarify and by way of example, the virion contains:
gp90 virus envelope protein, between 60% and 70% of mutations in the env gene are located in the sequences that codify gp90, given a quantity of mutations 3 times greater than the changes in gp45; by contrast to gp90, the envelope sequence of gp45 is highly conserved in all isolated samples of the EIA virus.
At the same time, with regard to the structural proteins of the predominant proteins in lentivirus up to 90% of the protein structure is codified by the gag gene, of which the p26 protein is the largest protein in the viral core. It is highly conserved in all isolated samples of the Equine Infectious Anaemia virus in the world. As such, all diagnostic tests are based on detection of antibodies for the p26 protein.
p26 is more antigenically stable in isolated EIAV than gp45 and gp90 glycoproteins (OIE Terrestrial Manual 2013 Chapter 2.5.6-2.1.1) and the one used in commercial diagnosis reagents.
While the ELISA can detect antibodies slightly earlier and in smaller concentrations than the AGID, a positive test result by ELISA should be retested using the AGID test to confirm the diagnosis because some false-positive results have been noted with the ELISA, which do not occur in immunodiffusion procedures because of the specificity of the identity reaction (OIE Terrestrial Manual 2013 Chapter 2.5.6, page 2).