EVALUATION OF ALTERNATIVE METHODS FOR THE DETECTION OF BOVINE LEUKEMIA-VIRUS IN CATTLE

Aim. To evaluate commercially available enzyme-linked immunosorbent as says (ELISAs) and the polymerase chain reaction (PCR) for their abilit y to detect antibodies against or nucleic acid of the bovine leukaemia virus (BLV), the causal agent of enzootic bovine leukosis (EBL), and to assess their usefulness in a national eradication programme. Method s. Eighty-two well-defined sera (including 18 from an OIE reference la boratory) and 399 field sera from New Zealand cattle were tested in fi ve ELISAs and the results compared with the agar gel immunodiffusion ( AGID) test and electrophoretic immunoblotting (EIB) results. A polymer ase chain reaction-based technique, which could detect BLV-RNA and pro viral-DNA, was also evaluated on a subsample of the field cases. Resul ts. Two commercial ELISAs classified 99% of the defined sera correctly , with the other three ranging in their correct classification between 88% and 95%. The ELISAs agreed in their general classification on the majority of the 399 blood samples (91.7%), and with the AGID for more than 95% of the sera. In a dilution series of the international refer ence serum E4, the highest dilution with a positive (or suspicious) re sult ranged from 1:80 to 1:5120. A dilution series of 202 field positi ve samples tested in the preferred ELISA detected 98% of positive sera at a 1:5 and 1:10 dilution, reducing to 78% at a 1:80 dilution of the sera. Agreement between serological tests and PCR was poor, mainly du e to failure of the PCR to detect a number of serologically positive a nimals. Conclusion. ELISA tests detected about 10% more reactors than the AGID and the EIB combined. Some ELISA-positive animals were not de tected by PCR, raising doubts about the usefulness of PCR-based techno logy in EBL eradication programmes.