Masked Genotype 6 of Bovine Leukemia Virus Is Found in Colombian Cattle

Abstract

Background Viral diseases such as bovine leukosis are a major cause of health problems associated with economic losses in the livestock industry worldwide. The prevalence of bovine leukosis ranges between 4% and 90%, and this disease is considered endemic. The etiological agent is bovine leukemia virus (BLV). Ten BLV genotypes have been reported based on analysis of complete or partial envelope gene sequences, of which genotype 1 is the most prevalent. However, the genetic variability of BLV variants circulating in Colombia remains unexplored. Therefore, in the present study, we analyzed blood samples collected from 289 cows distributed in 75 farms across the country. PCR amplification of env, gag and tax gene segments was performed. The obtained amplicons were sequenced and then subjected to phylogenetic analyses. Results A total of 62% of the cows present at 92% of the farms were BLV-positive. Genotype 1 was exclusively detected by env and gag gene segments when analyzed using previously reported primers. However, tax gene analysis revealed circulation of genotype 6 variants, which were also detected based on env gene analysis with newly designed primers. These results indicate that current genotyping approaches based on partial env sequencing may bias BLV genetic variability approaches and underestimate the diversity of the detected BLV genotypes. Conclusions This report is the first molecular and epidemiological study of BLV conducted in Colombia and contributes to the global epidemiology of the virus; it also reinforces the great impact of BLV on the country’s livestock and thus is a useful resource for farmers and government entities.