PROVIRUS VARIANTS OF THE BOVINE LEUKEMIA-VIRUS AND THEIR RELATION TO THE SEROLOGICAL STATUS OF NATURALLY INFECTED CATTLE

Infection of cattle with the bovine leukemia virus (BLV) results in a strong permanent antibody response to the BLV antigens some weeks afte r infection. However, cattle may carry provirus and not have detectabl e antibody titers. To prove the occurrence of different BLV provirus v ariants in German cattle and to study the influence of special BLV var iants on the immunoreaction, a 444-bp fragment of the env gene of 35 n aturally BLV infected animals was analyzed. Seven different groups of BLV provirus variants were found on the basis of restriction fragment length polymorphism. Three BLV provirus variant groups and five additi onally sequenced BLV isolates showed a high similarity to BLV provirus isolates from other geographical areas. The variation in nucleotide s equence of the five BLV isolates compared with nine previously sequenc ed BLV isolates ranged up to 5.3%. While BLV provirus variant groups A , C, D, E, F, and G were clearly related to agar-gel immunodiffusion t est (AGID)- and enzyme-linked immunosorbent assay (ELISA)-positive ani mals, BLV provirus variant group B was solely found in permanent AGID- and ELISA-negative or in transient ELISA-positive animals. Altogether , these results indicate that special BLV provirus variants may be res ponsible for atypical forms of BLV infection in cattle. (C) 1997 Acade mic Press.