Global distribution and host range of enzootic bovine leukosis in ruminants: A systematic review and meta-analysis

Enzootic bovine leukosis (EBL) causes severe economic losses and is a contagious disease caused by the Bovine Leukemia Virus (BLV), belonging to the delta retrovirus of the Retroviridae family. Thus, this review aimed to estimate the global pooled prevalence of enzootic bovine leukosis and investigate its host range, focusing on cattle and sheep. We used seven databases which include PubMed, Science Direct, HINARI, Scopus, Google Scholar, Web of Science, and AJOL. The included studies (50 articles), conducted between 1992 and 2024, represent diverse geographic regions: Asia, North America, Africa, South America, and Europe. 346,917 animals were involved, of which 99,620 involved positive for BLV. The meta-analysis estimated a pooled BLV prevalence of 19% (95% CI: 16%-23%) using random effect model, though significant heterogeneity existed across studies (I² = 99.6%, p < 0.001). Subgroup analysis revealed that the highest prevalence of EBL was in North America (43%), followed by Asia (17%), Africa (14%), South America (10%), and the lowest in Europe (4%). Analysis by publication year revealed that the prevalence of EBL was 32% after 2016, whereas it was 29% before 2016. Among animal species, beef cattle exhibited the highest prevalence (26%), followed by overall cattle (20%), sheep (19%), and dairy cattle (18%). Geographical and temporal trends revealed varying prevalence rates, with notable high rates in North America and lower rates in regions such as Europe. It is crucial that North America adopt stricter prevention programs, similar to those in Europe, to reduce transmission of EBL and its economic and health impacts on livestock.