A new rapid indirect ELISA test for serological diagnosis of feline immunodeficiency

The Feline Immunodeficiency Virus (FIV) is a lentivirus belonging to Retroviridae family that affects feline immune cells, causing a progressive immunosuppression by depleting CD4+ T-lymphocytes, similarly to the acquired immune deficiency syndrome (AIDS) in humans caused by human immunodeficiency virus (HIV). Diagnosis is usually performed by clinicians using rapid Enzyme-Linked Immunosorbent Assay (ELISA) or lateral flow tests that detect FIV antibodies. The aim of this work was the development of FIVCHECK Ab ELISA, a new rapid indirect assay for the detection of FIV antibodies in Vet. Sci. 2025, 12, 89 https://doi.org/10.3390/vetsci12020089 Vet. Sci. 2025, 12, 89 2 of 26 feline serum/plasma samples; FIVCHECK Ab ELISA was developed after a meticulous setup and cut-off analysis through several methods, including the Youden’s index and ROC curve, to achieve the best test performance. The new kit was validated by testing 115 feline sera (38 positives and 77 negatives for FIV antibodies) against the ELISA rapid test SNAP FIV/FeLV Combo (IDEXX). Moreover, 103 sera (28 positives and 75 negatives) were also analyzed with two other rapid indirect ELISAss, INgezim FIV (Gold Standard Diagnostics) and VetLine FIV (NovaTec); FIVCHECK Ab ELISA agreed at 100% with SNAP (100% sensitivity, 95% confidence interval (CI): 88.5–100%; 100% specificity, 95% CI: 94.0–100%), 100% with INgezim FIV and 92.2% with VetLine FIV. Intra- and inter-assay accuracy and precision gave coefficients of variation lower than 10%. The new ELISA is a simple and quick test that provides reliable results for veterinary clinics and practices