Equine infectious anemia (EIA) is a disease caused by a Lentivirus that is currently controlled exclusively by identification of seropositive animals. In most countries, including Brazil, the official diagnostic test for EIA is the agar gel immunodiffusion test (AGID). Although this assay has a high specificity it can produce false negative reactions or equivocal results due to weak precipitation lines, especially in samples from donkeys, mules or newly infected equids. In this pioneering study, it was used overlapping synthetic peptide pools to map and identify a consensus, widely recognised antibody epitope within env encoding the EIAV envelope proteins. A 20-mer soluble peptide encompassing this epitope (pgp45) was then synthesized and tested in an indirect ELISA test. Using a panel of 859 EIA positive and negative equid serum samples, the pgp45 ELISA had 96.1% concordance, 98.6% sensitivity and 95.6% specificity respectively, when compared to AGID. The sensitivity and specificity of the pgp45 ELISA was also >90% when tested in individual equid species including horses (Equus caballus), donkeys (Equus asinus) and mules (Equus caballus x Equus asinus). Moreover, in a horse experimentally infected with the pathogenic Wyoming EIAV strain viral-specific antibodies were detected at 10 days post-infection (dpi) whereas in AGID no specific antibody was detected until 18 days of experimental infection. This peptide can now be used as an antigen in serological tests, especially for rapid screening of large numbers of equids, where it may contribute significantly in the control of EIA, especially at sites with high populations of donkeys and mules.
Keywords: EIAV; Equidae; Indirect ELISA; Spot synthesis; gp45.
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