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Alcohol and alkalosis enhance excystation of Opisthorchis viverrini metacercariae

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The northeastern region of Thailand has long been known as an endemic area of the human liver fluke infection which is caused by Opisthorchis viverrini. Humans are infected by ingestion of uncooked cyprinoid fish in traditional dishes such as “koi-pla,” “pla-som,” “pla-jom,” and “pla-ra.” To date, the prevalence of this parasite infection remains high because of cultural behavior and local beliefs. The popular misunderstanding among people in this area is that alcohol, lemon juice, and fish sauce can kill the parasites. Thus, they believe that they can eat raw fish without the risk of infection. This study attempts to clarify the effects of ethyl alcohol and acidosis–alkalosis on O. viverrini metacercariae excystation. Metacercariae of O. viverrini were obtained from infected cyprinoid fish in a natural reservoir. Most metacercariae were obtained from small cyprinoid fish. Metacercariae were divided into three experimental groups and were treated with solutions containing four different concentrations of ethyl alcohol, four different concentrations of salt, and a range of acidic/basic pH. Metacercariae excystation was observed at the assigned times, and the data were then analyzed. Salt had no effect on excystation. Interestingly, the optimal conditions for O. viverrini excystation were pH 9 and 25 % ethyl alcohol. The present study suggests that raw fish should not be eaten while drinking alcohol or when consuming other ingredients with pH 9, because both alcohol and pH 9 could induce O. viverrini metacercariae excystation, leading to the early development of parasites in the hepatobiliary system.

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This research was supported by the Higher Education Research Promotion and National Research University Project of Thailand, Office of the Higher Education Commission, through the Health Cluster (Shep-GMS) Khon Kaen University, and TRF Senior Research Scholar Grant no. RTA5580004, Thailand. We thank the research affairs (AS54301), Faculty of Medicine Khon Kaen University, and Department of Parasitology for their support and Mr. Christopher Salisbury for the English editing.

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Correspondence to Thidarut Boonmars.

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Sriraj, P., Aukkanimart, R., Boonmars, T. et al. Alcohol and alkalosis enhance excystation of Opisthorchis viverrini metacercariae. Parasitol Res 112, 2397–2402 (2013).

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