POLYMERASE-CHAIN-REACTION (PCR) FOR DETEC TION OF BLV PROVIRUSES - USEFUL TOOL TO COMPLEMENT BLV DIAGNOSTICS

A typical infection with bovine leukemia virus (BLV) induces a permane nt antibody (Ab) response with high titers against BLV-antigens. In th e last few years atypical courses of infection with low or transient B LV-Ab-titers or even lack of any detectable BLV-Ab-titers in animals w ith BLV-provirus integration have been described. This makes it diffic ult to eliminate BLV infection from herds using serological assays onl y. Whether or not polymerase chain reaction (PCR) is a useful tool to complement serological Ab-assays in BLV-eradication in herds was clari fied in three ways: (i) different DNA-quick-preparations of blood were examined in nested PCR, (ii) cows of a BLV infected herd that was inv olved in a national eradication program were investigated for 6 months und (iii) BLV-provirus-variants occurring in this herd were different iated. The results show, that even by using PCR it was not possible to detect all infected animals all the time and that eradication of BLV from this herd was not completed in this short time, The PCR is useful for the investigation of herds and more sensitive than ELISA. PCR usi ng LTR-primers (34 positive cattle) was more sensitive than PCR with e nv-primers (30 positive cattle), Using PCR 33 BLV infected cattle were detected of which only 21 reacted in ELISA. Restriction enzyme analys is or sequence analysis of PCR-amplificates allowed the detection of v irus variants and conclusions about the way of infection. PCR should b e used for BLV-eradication in cattle herds with low BLV-incidence, for the investigation of new outbreaks or tumor cases in long term BLV fr ee herds and for investigation of breeding cattle.