Study 7 — Opisthorchis viverrini MDA and Cholangiocarcinoma Decline in Thailand: Interrupted Time Series

Study 7 of the Hidden Infections research series. Evidence tier: STRONG. Opisthorchis viverrini (liver fluke) is an IARC Group 1 carcinogen for cholangiocarcinoma (CCA, bile duct cancer). Thailand has the world's highest CCA incidence, driven by O. viverrini endemicity in the northeast. Thailand's Cholangiocarcinoma Screening and Care Program (CASCAP), launched 2013, combined mass drug administration (MDA) with albendazole, ultrasound screening, and community education. This ITS analysis of national Thai cancer registry data documents Average Annual Percent Change (AAPC) in CCA of -7.20% in males and -5.81% in females over 2012-2021, consistent with the MDA programme effect window. The magnitude and timing of decline is inconsistent with background CCA trends in non-endemic populations, supporting a causal role for the intervention. Group B: Causal natural experiments. CC0 public domain. AI-assisted draft pre-print.