Systematic review and meta-analysis for the occurrence of Crimean-Congo hemorrhagic fever, Tularemia, and Rift Valley fever in pastoralist systems in Africa

Introduction Pastoralism is a livestock production system practiced in areas with harsh environmental conditions and is characterized by low investment in animal health, increasing the risk of animal disease outbreaks. Zoonotic diseases such as Crimean-Congo hemorrhagic fever (CCHF), Rift Valley fever (RVF), and tularemia may spread through livestock product value chains. Methods Published studies on the three diseases were systematically searched in PubMed, Web of Science, Scopus, and Google Scholar using predetermined search terms. Eligible studies were screened, and full texts were reviewed for data extraction. Extracted variables included publication details, laboratory methods, and measures of disease occurrence. Studies were grouped according to livestock value chain nodes. Random-effects models were used to estimate pooled prevalence. Publication bias was assessed using Egger's test and funnel plot symmetry. A random forest algorithm identified relevant moderators of prevalence, which were further evaluated using mixed-effects models. Results A total of 34 studies were included, with RVF being the most studied pathogen (64.7%), followed by CCHF (29.4%) and tularemia (5.9%). RVF prevalence was highest in humans (29%; 95% CI: 7-69%), followed by camels (19%; 95% CI: 7-43%), and lowest in goats (6%; 95% CI: 4-10%). CCHF prevalence was highest in camels (48%; 95% CI: 8-91%) and lowest in humans (6%; 95% CI: 2-19%). At the value chain level, prevalence was highest at livestock farms for both RVF (13%; 95% CI: 10-16%) and CCHF (15%; 95% CI: 4-44%). Females were more likely to test positive (OR = 5.20; 95% CI: 3.09-8.76; p < 0.01), while mixed herds showed higher likelihood of RVF positivity (OR = 33.34; 95% CI: 0.72-1548.64; p = 0.0734). Tularemia had a pooled positivity rate of 2% (95% CI: 0-8%). Discussion This review provides evidence that CCHF, RVF, and tularemia are endemic in pastoral areas. Strengthened surveillance along livestock value chain nodes is needed to mitigate the risk of disease transmission.