Reactivity of serum from cattle suspected of bovine leukaemia virus infection to peptides representing mutated epitopes on envelope glycoprotein gp51

The ELISA technique with synthetic peptides as an antigen was developed to analyse the reactivity of bovine serum directed to mutated epitopes on envelope glycoptrotein gp51 of bovine leukaemia virus (BLV). The peptides represented normal and mutated G, H, and GG epitopes deduced from wild type BLV and its genetic variants, respectively. When 436 sera identified as seronegative by commercially available ELISA were tested by newly developed peptide ELISA, 14 samples revealed the highest reactivity. Out of them, reactivity to the mutated epitope GG was found in eight samples, while five and two samples reacted to epitopes G and H, respectively. One serum showed the reactivity to two peptides. Sera, which reacted with the epitope G, were found mostly in animals from one herd, while the distribution of sera that reacted to epitopes GG and H were less restricted to the particular herds. It has been concluded that sera showing strong reactivity to mutated peptides could represent animals infected with BLV variants, which escape antibody detection.