Spatial patterns and risk mapping of opisthorchiasis and soil-transmitted helminth infections in Thailand using Bayesian geostatistical models

Opisthorchis viverrini and soil-transmitted helminths (STH) remain major public health challenges in Thailand due to their widespread distribution. This study aimed to map and predict the prevalence of O. viverrini and STH infections across Thailand and to identify key environmental, climatic, and socio-economic factors influencing their geographical distribution. Bayesian geostatistical logistic regression models were fitted to national survey data to estimate infection risk and generate high-resolution spatial predictions. Demographic (sex, age), environmental (land surface temperature, vegetation indices, altitude), climatic (minimum and maximum temperature), and socio-economic (nighttime light intensity) variables were included as covariates in the models, and their associations with infection risk were quantified using posterior odds ratios and 95% Bayesian credible intervals (95% CrI). Opisthorchis viverrini infection was significantly associated with sex and age. Males had higher odds of infection than females (OR: 1.57; 95% CrI: 1.24-1.97). Individuals aged 25-59 years (OR: 4.75; 95% CrI: 3.22-7.21) and ≥ 60 years (OR: 4.69; 95% CrI: 3.10-7.29) had similarly elevated risks compared with those < 25 years. Minimum temperature (TMIN) was significantly negatively associated with infection risk. For each 1 °C increase in TMIN, the probability of O. viverrini infection decreased by 33% (OR = 0.67, 95% CrI: 0.49-0.88). Hookworm infection was more common among males (OR: 1.65; 95% CrI: 1.42-1.93) and individuals aged 25-59 years (OR: 1.86; 95% CrI: 1.52-2.28). For Ascaris lumbricoides, infection risk was lower in individuals aged 25-59 years (OR: 0.42; 95% CrI: 0.18-0.98) and negatively associated with land surface temperature (OR: 0.66; 95% CrI: 0.39-0.98) and nighttime light intensity (OR: 0.97; 95% CrI: 0.93-0.99). No statistically significant associations were detected for Trichuris trichiura. Spatial predictions showed that O. viverrini was concentrated in northeastern Thailand, whereas STH infections were most prevalent in the south. Distinct spatial heterogeneity was observed in the distribution of O. viverrini and STH infections in Thailand. Demographic factors were consistently associated with O. viverrini and hookworm infection, whereas selected environmental and socio-economic correlates were associated with A. lumbricoides. These findings support geographically targeted surveillance and control strategies focused on high-burden areas and vulnerable populations.