EVALUATION OF POLYMERASE CHAIN-REACTION (PCR) APPLICATION IN DIAGNOSIS OF BOVINE LEUKEMIA-VIRUS (BLV) INFECTION IN NATURALLY INFECTED CATTLE

The practical application of polymerase chain reaction (PCR) for the d iagnosis of bovine leukaemia virus (BLV) infections in naturally infec ted cattle was evaluated. Compared to serological tests the PCR was de finitely found to be a more sensitive method, yielding the highest num ber of positive results (10% more compared to enzyme-linked immunosorb ent assay, (ELISA), and 17.7% more compared to agar-gel immunodiffusio n, (AGID)). In testing cattle from herds with BLV incidence under 5%, out of 52 provirus positive cattle only 43 were correctly identified b y ELISA. When compared to AGID only 37 of the 52 PCR positive animals were correctly identified. Of 18 cattle imported from the Slovak Repub lic and kept in a quarantine stable, four were found to be BLV proviru s positive by PCR, while serological tests indicated one animal positi ve and three negative. Therefore, it is impossible to prevent the spre ad of the infection from one country to another by serological testing only. Moreover, it is feasible to identify animals with changing anti body titres correctly by PCR. Using PCR we were also able to distingui sh BLV infected from uninfected calves that were serologically positiv e due to colostral antibodies. Higher sensitivity of BLV provirus dete ction by PCR was achieved using env gene rather than tax gene specific primers. Negative results by PCR in cases of positive serological rea ctions are still possible, as shown in case of one adult animal. These findings indicate that PCR is a highly sensitive method and might be successfully used and economically advantageous for different practica l applications in detection of BLV infection in naturally infected cat tle.