Comparison Between Four Laboratory Tests for Routine Diagnosis of Enzootic Bovine Leukosis

Abstract

The aim of this study was to compare the diagnostic capabilities of the agar gel immunodiffusion test (AGID) and two types of PCR, nested PCR (with nucleic acid extraction from blood) and direct blood nested PCR (db nested PCR)-without extraction, vs. enzyme-linked immunosorbent assay (ELISA) as the gold standard in the routine diagnostics of this disease. A total of 409 blood samples were obtained from cattle 18 mo. to 5 yrs. of age, and all the samples were analyzed using the four assays. Following the initial testing, the samples were stored at-20°С and re-tested using all the four techniques after a month of freeze storage to determine the reproducibility of the results. ELISA detected 57 animals as positive (13.9%) versus 33 ones using AGID and 56 using the two types of nested PCR. AGID showed low sensitivity of 57.9% and moderate agreement compared to ELISA. In addition, AGID did not show consistency in the results from the two independent measurements. The two types of nested PCR showed nearly full agreement with ELISA with a kappa value of 0.99. Since AGID showed lower sensitivity and lack of reproducibility in the results for 22 samples as compared to the other techniques used in this study, we suggest that the future application of this test for the diagnosis of Enzootic bovine leucosis in blood samples should be reconsidered. On the other hand, db nested PCR demonstrated very good sensitivity and reproducibility of results, it also requires less sample processing. All this makes it potentially suitable for routine diagnostics.