This study aims to assess the efficacy, safety and acceptability of ascending doses of arpraziquantel in children infected with Opisthorchis viverrini. The primary objective is to determine the dose-response relationship in terms of cure rate. This study will involve children aged 6-7 years, since O. viverrini infections often occur in pre-school and school-aged children, and this group is largely left untreated in current public health programs.

Inclusion Criteria:

• Aged 6 to 7 years (i.e., 72 to 95 months).
• Written informed consent signed by parents/caregivers (signature or thumbprint).
• Agree to comply with study procedures, including provision of two stool samples at baseline and at follow-up assessment 21-28 days after treatment, respectively.
• Willing to be examined by a study physician prior to treatment.
• At least two slides of the quadruple Kato-Katz thick smears positive for O. viverrini.

Exclusion Criteria:

• Presence or signs of major systemic illness, e.g. severe anaemia (haemoglobin level of < 80 g/L according to WHO) upon initial clinical assessment.
• Known or suspected infection with Taenia solium (cysticercosis).
• Known or suspected acute schistosomiasis.
• Abnormal liver and kidney function.
• Use of anthelminthic drugs within 4 weeks before or during study period.
• Known allergy to study medications (i.e. praziquantel or any of the excipients).
• Being prescribed or taking concomitantly medication with known contraindication or drug interactions with the study medication.
• Concurrent participation in other clinical trials.