Prevalence of subclinical mastitis, its associated bacterial isolates and risk factors among cattle in Africa: a systematic review and meta-analysis

Background: Subclinical mastitis (SCM) is one of the most economically important diseases affecting the dairy industry. The SCM does not cause visible changes in the udder or physical changes of the milk as compared to clinical mastitis, and a clear overview of the prevalence and risk factors in the different regions of Africa is still lacking. The objective of this study was to investigate the prevalence of SCM and assess the associated risk factors and dominant bacterial pathogens among cattle in Africa. Materials and methods: Using a systematic review and meta-analysis approach, we gathered literature concerning SCM among cattle in Africa, published from 2020 through 2021in five databases. Results: A total of 1,560 records were retrieved and at the end of the screening, 38 studies were eligible for inclusion in the meta-analysis. The random-effects meta-analysis model showed that the weighted pooled prevalence of SCM in cattle in Africa was 51.5% (95% CI: 44.0-58.9%). Heterogeneity was high and significant as I2 (proportion of observed variation) was 98.4% (95% CI: 97.6-99.0%), τ2 was 0.0533 (95% CI: 0.035-0.089), and the Cochran Q statistic was 2244.97 (p<0.0001). Sub-group and meta-regression analyses showed that West Africa had the highest point estimate (85.3%), followed by East Africa (64.1%), and the least was for southern Africa (16.3%) (p=0.007). Other significant moderators for SCM were age (p<0.0001), breed (p=0.015) and parity (p=0.0001) of cattle. Staphylococcus species were the most predominant pathogens, followed by Streptococcus and Escherichia spp. Conclusions: The present study showed a high variation of subclinical mastitis prevalence in various parts of Africa. There is a need for more data on subclinical mastitis in some regions on the continent. The information gathered in this paper may be used to guide a multidisciplinary approach to the management, control and reduction of this infection.