Big Six: Vertebrate host interactions as significant transmission drivers of bovine trypanosomosis in Nigeria – A systematic review and meta-analysis

Abstract

Bovine trypanosomosis remains a significant challenge in Nigeria due to the widespread presence of tsetse and biting flies. Despite numerous control interventions, livestock owners continue to face the burden of high treatment costs year-round. Holistic management has been elusive, largely due to the interconnected roles of the "Big-Six" animal hosts in sustaining transmission dynamics. This study conducted a systematic review of publications from Web of Science, Ovid MEDLINE, PubMed, Google Scholar, and AJOL Online databases, following PRISMA guidelines between 2000 and 2024. Eligible studies reported trypanosomosis prevalence in cattle, small ruminants, dogs, pigs, camels, and wildlife. Subgroup analyses by breed, sex, and diagnostic techniques were performed, with point estimates evaluated at a 95 % confidence interval (CI). A total of 80 studies involving 25,171 animals were included, revealing average prevalence of 38.2 % (95 % CI: 31.4–45.3) in wildlife, pooled prevalence of 12.0 % (95 % CI: 3.0–25.1) in cattle, with 11.7 % specifically observed in trypanotolerant cattle breeds, 4.6 % (2.3–7.6) in small ruminants, 9.6 % (95 % CI: 1.9–21.5) in dogs, 10.4 % (95 % CI: 5.6–16.3) in pigs, and 28.0 % (95 % CI: 18.5–38.6) in camels. Wildlife exhibited distinct ecological patterns, while ovine and caprine data clustered closely. These findings explain the critical role of vertebrate hosts, along with bovine herd management practices, in perpetuating disease transmission within susceptible cattle populations. Effective control requires treating vertebrate hosts harbouring trypanosomes within or surrounding bovine herds and the use of insecticide-impregnated nets, alongside fencing cattle herds from forest edges. This integrated approach is essential to achieving the elimination of African animal trypanosomosis (AAT) in Nigeria and across Africa.