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

Bovine leukaemia virus (BLV) causes chronic lymphoproliferative disorder and fatal lymphosarcoma in cattle, leading to significant economic losses in the beef and dairy industries. BLV is endemic globally and eleven genotypes have been identified. To date, only Zambian isolates have been genotyped from Africa. Although high BLV prevalence has been reported in South Africa, there has been no molecular characterisation of South African BLV isolates. To characterise BLV isolates in South Africa for the first time, we investigated the phylogenetic relationships and compared the genetic variability of eight South African BLV isolates with BLV isolates representing the eleven known genotypes from different geographical regions worldwide. Phylogenetic analyses based on full-length and partial env sequences as well as full-length gag sequences revealed that at least two genotypes, genotypes 1 (G1) and 4 (G4), are present in cattle in South Africa, which is consistent with studies from Zambia. However, our analysis revealed that the G1 South African isolate is more similar to other G1 isolates than the G1 Zambian isolates whereas, the G4 South African isolates are more divergent from other G4 isolates but closely related to the G4 Zambian isolate. Lastly, amino acid sequence alignment identified genotype-specific as well as novel amino acid substitutions in the South African isolates. The detection of two genotypes (G1 and G4) in southern Africa highlights the urgent need for disease management and the development of an efficacious vaccine against local strains.