Prevalence and genotyping of Giardia duodenalis infections in humans in Thailand: a systematic review and meta-analysis.

BACKGROUND: Giardia duodenalis remains a neglected parasitic infection in Thailand, with uncertain national prevalence and limited data on genetic assemblages. This systematic review and meta-analysis aimed to estimate the pooled prevalence of G. duodenalis infections in Thailand and assess the distribution of assemblages to inform surveillance and control strategies. METHODS: The protocol for this study was registered in PROSPERO (CRD42024629406). A comprehensive search was conducted across six databases: EMBASE, Ovid, PubMed, Scopus, Nursing & Allied Health Premium, and the Thai-Journal Citation Index (TCI). The methodological quality of included studies was assessed using the Joanna Briggs Institute (JBI) critical appraisal checklist for observational studies. A meta-analysis using random-effects models estimated the pooled prevalence of G. duodenalis infections and the distribution of assemblages. RESULTS: Sixty-three studies comprising of 47,989 participants were included. The prevalence of G. duodenalis infection varied substantially by diagnostic method, ranging from 1.40% using direct smear microscopy to 1.99% using concentration techniques, 3.66% with culture-based methods, 13.44% with immunoassays, and 8.98% with molecular techniques (P < 0.0001). Prevalence also differed geographically, with the highest estimates in Western Thailand (12.22%) and the lowest in Northeastern Thailand (0.54%). Vulnerable groups, including orphans (15.14%) and preschool children (11.73%), carried a disproportionate burden of infection. Among the 240 samples analyzed by molecular methods, Assemblage B was the most common (55.0%), followed by Assemblage A (32.5%), mixed A/B infections (12.08%), and a single case of Assemblage F (0.42%). CONCLUSION: G. duodenalis remains endemic in Thailand, with transmission concentrated in socially vulnerable groups and regions with higher environmental risk. The predominance of Assemblage B and the underuse of molecular diagnostics highlight critical gaps in understanding transmission pathways. These findings suggest that control strategies in Thailand should prioritize high-risk populations and incorporate molecular epidemiology into routine surveillance to more effectively guide prevention efforts. CLINICAL TRIAL: Not applicable.