Global prevalence and epidemiological determinants of African horse sickness: A systematic review and meta-analysis.

Overview

• This study systematically reviewed and analyzed published research to estimate the global prevalence of African horse sickness (AHS) and explore the factors causing variation in its occurrence.
• It aimed to provide a comprehensive quantitative summary of the epidemiology of AHS, a lethal viral disease affecting equids transmitted by insect vectors.

Background

• African horse sickness (AHS) is a highly fatal viral disease primarily affecting horses and related species (equids).
• It is transmitted by biting midges (vectors), causing significant economic losses and animal welfare concerns, especially in endemic regions within Africa.
• Despite many individual studies, prevalence estimates have varied widely due to differences in study design, geography, and diagnostics.
• A comprehensive quantitative synthesis of these studies was lacking, motivating the present systematic review and meta-analysis.

Methods

• The review followed PRISMA 2020 guidelines to ensure transparent and reproducible systematic review processes.
• The protocol was registered on the Open Science Framework to increase study transparency and reduce bias.
• Seven scientific databases were searched comprehensively for observational studies reporting on AHS prevalence in equids.
• Eligibility criteria focused on studies providing prevalence data, conducted over various time periods and geographic regions up to 2025.
• The quality of included studies was evaluated using the Joanna Briggs Institute checklist, assessing risk of bias and methodological rigor.
• Prevalence estimates were pooled using a random-effects meta-analysis model with logit transformation to handle variability and stabilize variance.
• Statistical heterogeneity was assessed via I² (percentage of variation due to heterogeneity) and τ² (between-study variance).
• Subgroup analyses and meta-regression were conducted to identify potential sources of heterogeneity such as host species, geography, age, diagnostic methods, season, and time period.
• Publication bias was assessed using funnel plots and Egger’s test, which detect whether smaller studies with negative or low prevalence findings might be underreported.
• All analyses were conducted using RStudio software (version 4.4.2), a common tool for statistical computing.

Results

• Twenty-five eligible studies published between 1978 and 2025 were included in the meta-analysis.
• The overall pooled global prevalence of AHS was estimated at approximately 50.34% (95% Confidence Interval: 26.95% to 73.58%), indicating that about half of the examined equid populations were affected on average.
• Considerable heterogeneity was observed across studies, with I² = 98.1% indicating that the vast majority of variability was due to differences between studies rather than chance alone.
• The high τ² value (6.3284) and wide prediction interval (0.50% to 99.51%) implied very diverse prevalence depending on the context, geographic location, time, and study characteristics.
• Subgroup analyses showed large differences in prevalence based on host species (different types of equids), age groups, geographic regions, diagnostic methods used, seasonal timing of studies, and study periods.
• Meta-regression found no statistically significant temporal trend in prevalence, meaning the disease burden did not clearly increase or decrease over the decades studied.
• Funnel plot asymmetry and results from Egger’s test suggested some degree of publication bias, implying studies with certain prevalence results may be more likely to be published.

Conclusions

• African horse sickness remains a highly prevalent and epidemiologically complex disease globally, especially in endemic areas.
• The large variability across studies highlights the need to consider multiple factors when interpreting prevalence data.
• Key recommendations include strengthening surveillance systems to better detect and monitor cases, implementing targeted vector control strategies to reduce transmission, and standardizing epidemiological reporting methods to enhance data comparability.
• Improved understanding of epidemiological heterogeneity will inform better prevention and control measures, ultimately mitigating the economic and health impact of AHS.
• The study emphasizes ongoing vigilance and preparedness on a global scale due to AHS’s significant disease burden and potential for spread.