Validation of an indirect <i>in‐house</i> ELISA using synthetic peptides to detect antibodies anti‐gp90 and gp45 of the equine infectious anaemia virus
Romina Cecilia Russi, Lucila García, Marı́a S. Cámara, Adriana Soutullo
Abstract
Summary Background Equine infectious anaemia (EIA) is controlled by the identification of seropositive animals. The official diagnostic method is the agar gel immunodiffusion (AGID) test, which detects antibodies against a viral core protein (p26). Although AGID is inexpensive and specific, the report of results takes considerable time and the test has low analytical sensitivity. Objective To validate our in‐house indirect ELISA gp90/45 , following the World Organization of Animal Health (OIE) criteria. Study design Test validation. Methods Synthetic peptides gp90 and gp45 were used as antigens in ELISA gp90/45 . Tests used for validation, calibration and linear working operating range, analytical and diagnostic sensitivity and specificity, repeatability and reproducibility were assessed by comparing them with the AGID test and using 1844 equine sera grouped into five different panels. Results We were able to replace the National References Sera with our Internal Reference Sera. ELISA gp90/45 had acceptable repeatability and reproducibility. Analytical sensitivity of the ELISA gp90/45 was 800 times greater than that of AGID test for positive sera and 400 times greater for weak positive sera. ELISA gp90/45 also showed optimal analytical specificity, since no cross‐reactivity was detected with antibodies against other equine viruses. One sample was positive by AGID test and negative by ELISAgp90/45. ELISA gp90/45 was performed using 243 EIA positive and 878 negative equid sera, and showed a diagnostic sensitivity of 99.59% [CI 97.73%‐99.99%] and a diagnostic specificity of 90.32% [CI 88.17%‐92.19%], compared to AGID test; thus, it was demonstrated to be a robust test. Main limitations Samples were derived from naturally infected equid populations showing heterogeneous clinical states: therefore, their status was uncertain and some horses were sampled more than once. The AGID test may not be the most useful gold standard. Conclusion ELISA gp90/45 is a useful tool for the diagnosis of EIAV infection and meets validation requirements established by the OIE.