Bacterial Symbionts Associated with Wild Tsetse Flies (Diptera: Glossinidae) in Sub-Saharan Africa: A Systematic Review and Meta-Analysis

Bacterial symbionts play a significant role in the biology of tsetse flies (genus Glossina). However, their infection prevalence in Glossina spp. is not well documented. Hence, the systematic review followed PRISMA guidelines to determine bacterial infection prevalence among different Glossina spp. across sub-Saharan Africa. Six databases were used to search for studies published between 1980 and 2024. The search was conducted from February to March 2025. Meta-analysis was conducted using estimated pooled infection prevalence of bacterial symbionts in different Glossina species. Spearman’s rank correlation coefficient was calculated to examine changes in bacterial infection prevalence between 2010 and 2024. A total of 30 studies from 19 countries met the inclusion criteria and were included in the final systematic review. Of the 30 studies, 173 records were extracted consisting of data from 14 Glossina species. Burkina Faso (n = 25) recorded highest number of studies and G. pallidipes (n = 27) was the most studied species. Significant associations were observed between bacterial infection prevalence and the tested variables (Glossina spp. and country). Temporal analysis results showed positive association in Spiroplasma infection prevalence over the years (rho = 0.418, p = 0.017) whilst Sodalis infections showed negative association (rho = −0.319. p = 0.008). Heterogeneity among different studies was substantially high (I2 > 75%) and evidence of publication bias was reported. The results indicated that bacterial infection prevalence was influenced by factors such as country, sample size and symbiont-specific species. However, heterogeneity remained high even after meta-regression analysis suggesting that other variables not included in the analysis or rather the combination of different variables are responsible for the high heterogeneity observed. Despite study limitations, the study provided the most comprehensive and complex results on the relationship between bacterial symbiont infections and Glossina species.