Molecular characterization of bovine leukemia virus from Moldovan dairy cattle

Abstract

Bovine leukemia virus (BLV) is the causative agent of enzootic bovine leukosis (EBL), a disease that has worldwide distribution. Whilst it has been eradicated in most of Western Europe and Scandinavia, it remains a problem in other regions, particularly Eastern Europe and South America. For this study, in 2013, 24 cattle from three farms in three regions of Moldova were screened by ELISA and nested PCR. Of these cattle, 14 which were PCR positive, and these were molecularly characterized based on the nucleotide sequence of the env gene and the deduced amino acid sequence of the encoded gp51 protein. Our results demonstrated a low level of genetic variability (0-2.9%) among BLV field strains from Moldova, in contrast to that observed for other retroviruses, including human immunodeficiency virus (HIV) (20-38%) Mason IL (Trudy vologod moloch Inst 146–164, 1970) and equine infectious anemia virus (EIAV) (~40%) Willems L et al (AIDS Res Hum Retroviruses 16(16):1787–1795, 2000), where the envelope gene exhibits high levels of variation Polat M et al (Retrovirology 13(1):4, 2016). Sequence comparisons and phylogenetic analysis revealed that BLV genotype 7 (G7) is predominant in Moldova and that the BLV population in Moldovan cattle is a mixture of at least three new sub-genotypes: G7D, G7E and G4C. Neutrality tests revealed that negative selection was the major force operating upon the 51-kDa BLV envelope surface glycoprotein subunit gp51, although one positively selected site within conformational epitope G was detected in the N-terminal part of gp51. Furthermore, two functional domains, linear epitope B and the zinc-binding domain, were found to have an elevated ratio of nonsynonymous to synonymous codon differences. Together, these data suggest that the evolutionary constraints on epitopes G and B and the zinc-binding domains of gp51 differ from those on the other domains, with a tendency towards formation of homogenous genetic groups, which is a common concept of global BLV diversification during virus transmission that may be associated with genetic drift.

Phylogenetic Analysis of South African Bovine Leukaemia Virus (BLV) Isolates

“…The Env mutations in the South African isolates appeared to be concentrated in the conformational epitopes (F, G and H) and the ND2. These results are consistent with previous studies showing that the G epitopes, particularly residues 48, 74 and 82, are under positive selection and are the most polymorphic sites [ 51 , 73 , 74 , 75 ]. Homology modelling of the BLV Env protein has suggested that the conformational epitopes and the neutralising domains are located on the surface of the virus [ 14 , 73 ].…”

Molecular Characterization of Bovine Leukaemia Virus (BLV) Strains Reveals Existence of Genotype 6 in Cattle in India with evidence of a new subgenotype

“…However, these substitutions have previously been observed in other BLV strains of genotype 6 indicating their genotype specificity (Lee et al., ; Polat, Takeshima et al., ). Substitutions at other residues within epitope G has been observed also in some other BLV genotypes indicating its role in virus evolution and generation of escape mutants (Pluta et al., ; Polat, Takeshima et al., ; Zhao & Buehring, ). Although in general BLV env gene is subjected to negative selection, strong positive selection has been reported in residues of epitope G (Zhao & Buehring, ).…”

New evidence of bovine leukemia virus circulating in Myanmar cattle through epidemiological and molecular characterization

“…Therefore, the gp51 region has been widely used for BLV genotyping and phylogenetic studies for the identification of viral strains isolated from different geographical regions. Globally, at least 11 different genotypes have been identified [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36].…”