Opisthorchis viverrini infection is still one of the public health problems in Southeast Asia. In Thailand alone, more than three million people are estimated to be currently infected. Opisthorchiasis may cause severe biliary diseases, eventually leading to fatal cholangiocarcinoma. This study aimed to investigate the prevalence and risk factors of opisthorchiasis in two rural communities along the Nam Kam River in the northeastern region of Thailand. A cross-sectional study was conducted in Phon Na Kaeo District of Sakon Nakhon Province and That Phanom District of Nakhon Phanom Province in Thailand between March and June 2017. Faecal samples were collected and examined for the presence of O. viverrini by Kato-Katz technique. Socio-demographic variables and risk factors were collected by a standardised questionnaire. The overall prevalence of O. viverrini among 495 study participants was 15.4% (95% confidence interval [CI] 12.3 – 18.8). The parasite rate was higher in Nakhon Phanom than in Sakon Nakhon (P = 0.009) and differed significantly in adults <45 years old in both provinces (P <0.05). Multivariate regression analyses revealed being labourer (adjusted odd ratio [AOR] 4.7 [95% CI 1.08, 20.38], P = 0.039) and farmer (AOR 5.79 [95% CI 1.45, 31.91], P = 0.015) were positively associated with a higher risk of O. viverrini infection. This study highlights O. viverrini infection as a significant endemic disease with potential health problems among the water-based communities along the Nam Kam River. For country with high O. viverrini transmission, such information will be useful for designing efficient strategic interventions.

Opisthorchiasis is endemic in parts of Southeast Asia, including the northern and northeastern regions of Thailand. In these regions, the transmission by fish intermediate hosts has received little attention. We investigated the intensity of Opisthorchis viverrini metacercariae (OV MC) in wild cyprinid fishes from five districts within the Nakhon Phanom Province, Northeast Thailand. Fishes were procured from local markets in five districts throughout three different seasons (hot, rainy and cold) between February 2018 and January 2019. The samples were identified, counted and weighed before metacercariae detection was performed via the artificial digestion method. A total of 2,149 freshwater fishes, representing 20 species were collected. The fish most commonly contaminated with OV MC were Anematichthys repasson and Hampala dispar. The intensity of OV MC in Nakhon Phanom was 0.23 OV MC/fish and varied among districts, ranging from 0.07 to 0.52. A low intensity of OV MC/fish (defined as <1 cyst) was found in all three different seasons in the Nakhon Phanom Province; hot season (0.55), cold season (0.22) and the rainy season (0.13). The intensity of OV MC/fish was moderate (defined as >1 cyst) in the Renu Nakhon district (2.5) in the hot season. By fish species, H. dispar yielded the highest, with a moderate intensity of 2.1. In natural freshwater cyprinid fish in Nakhon Phanom, OV MC infection is endemic with intensity rates varying according to district, season and fish species.