Brucellosis prevalence in Nigerian livestock: a systematic review and meta-analysis

Abstract

Brucella spp. are priority neglected zoonotic pathogens whose true burden in endemic settings remains systematically obscured by diagnostic heterogeneity. Although a prior systematic review has summarised brucellosis prevalence in Nigerian livestock, whether reported prevalence differences across studies reflect genuine epidemiological variation or methodological artefacts of diagnostic tool choice has not previously been formally tested using multivariable meta-regression, a distinction with fundamentally different policy consequences. This study aimed to estimate the pooled prevalence of brucellosis in Nigerian domestic animals and to formally quantify the contribution of diagnostic method, host species, geographic region, sample type, and sampling context to between-study heterogeneity. We conducted a systematic review and multivariable meta-regression of 98 publications (181 study arms; 72,362 animals; 9,785 positive cases) from PubMed, Scopus, Web of Science, and African Journals Online (AJOL), identified from a search covering 1 January 2000 to 31 December 2025 following PRISMA 2020 guidelines; the earliest eligible study was published in 2003, so the included evidence base spans 2003–2025 (23 years). The overall pooled brucellosis prevalence was 12.0% (95% CI: 10.0–14.0%; I²=97.3%, p < 0.001). Prevalence was highest in horses (26.0%, 95% CI: 11.0%-51.0%) and lowest in avian species (3.0%, 95% CI: 2.0–4.0%). Diagnostic method emerged as the dominant explainable source of between-study heterogeneity (R²=25.4%) as the confirmatory ELISA + LFA+Culture combination had 49.0% (95% CI: 45.0–53.0%; k = 4 study arms) in comparison to 6.0% for RBPT alone (95% CI: 4.0%-10.0%; k = 42), an eight-fold difference. Hygroma fluid had the highest sample type positivity (54.0%, 95% CI: 27.0%-79.0%). The multivariable model explained 51.2% of between-study variance (QM[df = 45] = 158.68, p < 0.001). No significant temporal trend was identified across 23 years of surveillance (β = −0.008, p = 0.603). These findings reframe the Nigerian brucellosis evidence base and argue urgently for World Organisation for Animal Health-aligned standardised diagnostic methods, species-targeted surveillance, and integrated One Health control strategies.