Prevalence and genetic characterization of bovine leukemia virus from beef cattle in the traditional sector in Zambia

Abstract

Bovine leukemia virus (BLV), the causative agent of enzootic bovine leucosis (EBL), is a member of the family Retroviridae, and genus Deltaretrovirus. Whilst BLV has been associated with considerable economic losses in the cattle industry worldwide, there is paucity of information on the molecular epidemiology of BLV infection in cattle in many African countries, including Zambia. Moreover, much of the work that has been conducted on BLV has focused on the dairy cattle sector where it has been identified to be a major constraint. Only limited studies have been conducted on the virus in beef cattle. This study was conducted to determine the prevalence and molecular epidemiology of BLV in beef cattle reared in the traditional sector in Zambia. Archived whole blood samples from 880 animals (188 from Southern, 342 from Eastern and 350 from Western provinces of Zambia), were pooled, with each pool containing blood samples from 10 animals giving a total of 88 pools. Total genomic DNA was extracted from the pools and a segment of the env gene of BLV was amplified by nested polymerase chain reaction (PCR). Amplicons of positive samples were sequenced by the Sanger di-deoxy chain termination method and phylogenetic analysis was conducted to determine the evolutionary relationships of BLV isolated from the study areas within Zambia. The env gene of BLV was detected in 19.3% (17/88) of pooled whole blood samples and the overall estimated pooled prevalence was 2.1%. Out of these 17 positive pools, 10 were from Southern and Western provinces (i.e. five positive pools from each province) and seven were from Eastern Province. The pooled prevalence by province was estimated to be 3.0%, 1.5% and 2.2% for Southern, Western and Eastern provinces, respectively, there was no significant difference in the proportion of positive pools among the three provinces. Phylogenetically, all the Zambian BLV detected from beef cattle in this study belonged to genotype I therefore only one genotype was detected. The BLV strains detected in the study formed a distinct cluster, suggesting long-term independent evolution within the country. Results from this study suggest that genotype I BLV is circulating in the major traditional beef cattle rearing regions of Zambia. This is the first study on the molecular detection and characterization of BLV from traditional beef cattle in Africa. Further studies are required to gain additional insights into BLV infections in other parts of the country to contribute to the development of prevention and control measures. Keywords: Bovine Leukemia Virus, Traditional, Beef Cattle, Molecular Characterization.