Longitudinal changes and risk factors of Opisthorchis viverrini infection after selective praziquantel treatment: evidence from urine antigen assay and fecal examination in an endemic community in Northeast Thailand

Abstract

Opisthorchis viverrini infection remains an important public health problem in Southeast Asia, particularly among rural populations in Northeast Thailand. Despite control efforts, transmission remains uninterrupted due to persistent behavioral and environmental factors. To better understand the longitudinal patterns of opisthorchiasis after selective praziquantel treatment, this study aimed to determine the incidence and reinfection rates in the study population and identify risk factors associated with O. viverrini infection. Based on a prospective study, the status of opisthorchiasis was monitored in a cohort of participants (n = 612) in Northeast Thailand using the formalin-ethyl acetate concentration technique (FECT) and O. viverrini antigen detection in urine by Enzyme-linked immunosorbent assay (ELISA). The baseline prevalence of O. viverrini infection was 41.0% by urine antigen assay, compared to 8.1% by FECT. Over the 24-week study period, the calculated incidence of infection was 64.6/100 person-years, and the reinfection rate after PZQ treatment, as measured by urine ELISA, was 63.7/100 person-years. Based on FECT, a tenfold lower incidence (7.5/100 person-years) and reinfection rate (5.9/100 person-years) were observed. Risk factor analysis identified raw fish consumption in the previous 6 months (aRR = 7.52; p < 0.001), frequent raw fish consumption (>10 times per month) (aRR = 3.60; p < 0.001), and previous praziquantel treatment aRR = 1.49; p = 0.032) as significant risk factors for infection. The results demonstrated that the persistence of opisthorchiasis prevalence is driven mainly by the incidence of infection and reinfection after chemotherapy, as assessed by urine antigen assay and FECT. Behavioral risk factors, particularly the consumption of raw fish, remain the primary risk of parasite transmission. Therefore, comprehensive intervention measures consisting of sensitive diagnostics, drug treatment, and culturally appropriate interventions are required.