Comparison of 2 commercial antibody ELISA kits for identification of high proviral load carrier cattle in strategic control of bovine leukemia virus infection

Bovine leukemia virus (BLV; family Retroviridae , taxon species Deltaretrovirus bovleu ) infection poses a serious threat to cattle health, and the strategic identification of high proviral-load (PVL) carriers is essential for disease control. We evaluated 2 commercial ELISA kits for the detection of BLV antibodies and indirect identification of high-PVL cattle (EBL ELISA [Nippon Gene] and Leukosis Serum X2 [Idexx]) using a cross-sectional survey of 155 cattle from 17 farms. Based on our quantitative real-time PCR (qPCR) results, we classified tested cattle into non-infected, low-PVL (<400 copies/10 ng DNA), and high-PVL (≥400 copies/10 ng DNA) groups. The 2 ELISA kits had excellent agreement (κ = 0.97; 95% CI [0.93, 1.00]) and moderate correlation ( r  = 0.617). In a receiver operating characteristic curve analysis, the Leukosis Serum X2 ELISA performed better than the EBL ELISA at identifying high-PVL cattle, with a higher area under the curve (0.840 vs. 0.785) and higher sensitivity (89.7% vs. 84.6%) and specificity (66.4% vs. 56.9%). Both ELISA kits had a moderate ability to distinguish high-level BLV-infected cattle. Our results suggest that a 2-step screening concept could be valuable: ELISA screening followed by confirmatory qPCR testing to identify cattle with a high PVL.