Feline Leukemia Virus in Cats: A Novel Rapid ELISA Assay for p27 Antigen Detection

Feline leukemia virus (FeLV) is an oncogenic immunosuppressive virus belonging to the <i>Retroviridae</i> family and one of the most common causes of a major infectious disorder in cats that can lead to potentially fatal associated diseases with a worse prognosis. FeLV infects and replicates in hematopoietic and lymphatic cells causing anemia, lymphoma, and leukemia. Diagnosis is usually performed by clinicians using the enzyme-linked immunosorbent assay (ELISA) or lateral flow tests that detect the p27 FeLV antigen. The aim of this work was the development of the FeLVCHECK Ag ELISA, a new rapid direct sandwich ELISA assay that detects the p27 antigen of FeLV. Assay cut-off was estimated by multiple approaches, including the Youden index and the ROC curve, to obtain the optimal test performance. The new test was validated by using 112 feline sera (42 positives and 70 negatives for FeLV) against the ViraCHEK/FeLV ELISA (Zoetis) as a reference, which agreed at 97.3%, with 97.6% sensitivity (95% confidence interval (CI): 86.0%-99.9%) and 97.1% specificity (95% CI: 89.1%-99.5%). Compared with another rapid and direct ELISA, the INgezim FeLV DAS (Gold Standard Diagnostics), the agreement was 90.2%. The new ELISA is both accurate and precise, with intra and inter-assay coefficients of variation (CV) below 10%. Accelerated and real-time stability studies set the shelf life of the kit at 18 months. This study clearly suggests that the FeLVCHECK Ag ELISA can be a valuable tool in clinical practice, as it provides very rapid and reliable results without the need for sample preparation or particular laboratory equipment since all incubations are performed at room temperature.