Comparison of the validity of different serological and molecular tests for Bovine Leukemia Virus in the Xth region of Chile
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Bovine leukemia virus (BLV) is a retrovirus that causes economic losses in the livestock sector. Transmission occurs mainly horizontally via infected blood cells. Infected animals can be healthy carriers, have persistent leucocytosis, or have lymphosarcomas. The objective of the study was to compare the validity of different serological and molecular tests to find out which test could best be used in different stages of a BLV controlling and eradication program in Chile. Milk, serum and EDTA blood were collected from 400 dairy cows, originating from 72 different farms in the Xth region of Chile. An agar gel immunodiffusion (AGID) test, enzyme-linked immunosorbent assay (ELISA) serum test and ELISA milk test were compared to a PCR test, which was chosen as the golden standard. Sensitivity (SE), specificity (SP) and, for the ELISA tests, ROC curves and optimal cut-off points were calculated. The SE and SP for ELISA serum were respectively 90,8 (87,6; 94,0) and 78,3 (71,2; 85,4), for ELISA milk 88,0 (84,4; 91,6) and 77,5 (70,3; 84,7) and for AGID 85,2 (81,1; 89,2) and 86,1 (79,9; 92,2). The area under the curve was for the ELISA serum 0,884 (0,845; 0,922) and for ELISA milk 0.862 (0,821; 0,902). Statistically the test were comparable to each other, with slight differences between them. The tests that were validated in this study were not optimal for a complete eradication program, because sensitivity and specificity are not one hundred percent. Therefore, complementary management measures are critical to reduce transmission.