Simplified Techniques for Killing the Carcinogenic, Opisthorchis Viverrini Metacercariae in Cyprinid Fish

Document Type: Research Articles

Authors

1 Department of Parasitology, Faculty of Medicine, Khon Kaen University, Khon Kaen 40002, Thailand.

2 Neglected, Zoonosis and Vector-Borne Disease Group, Faculty of Medicine, Khon Kaen University, Khon Kaen 40002, Thailand.

3 Liver Fluke and Cholangiocarcinoma Research Center, Cholangiocarcinoma Screening and Care Program (CASCAP), Khon Kaen University, Khon Kaen 40002, Thailand.

4 Department of Thai Traditional Medicine, Faculty of Natural Resources, Rajamangala University of Technology Isan Sakon nakhon Campus, Sakon Nakhon, 47160, Thailand.

5 Department of Anesthesiology, Faculty of Medicine, Khon Kaen University, Khon Kaen 40002, Thailand.

6 Faculty of Veterinary Medicine, Khon Kaen University, Khon Kaen 40002, Thailand.

7 Department of Surgery, Faculty of Medicine, Khon Kaen University, Khon Kaen 40002, Thailand.

8 Department of Biochemistry, Faculty of Medicine, Khon Kaen University, Khon Kaen 40002, Thailand.

9 Department of Parasitology, Graduate School of Medicine, Gifu University, Gifu 501-1194, Japan.

10 Department of Community Medicine, Faculty of Medicine, Khon Kaen University, Khon Kaen 40002, Thailand.

Abstract

 
Consumption of fluke-free fish is the most important factor in controlling Opisthorchis viverrini (OV) infection in endemic areas such as northeast Thailand and thereby reducing the risk of cholangiocarcinoma. Cooking fish is the best way to avoid infection; however, the cultural practice of eating raw or fermented fish is difficult to change. We investigated the food preparation process, using freezing, heating and fermentation to kill OV metacercariae in fish. Uncooked cyprinid fish infected with OV were divided into three groups: refrigerated at 4 oC for 24, 48 or 72 h (control group); frozen at -20 oC for 24, 48 or 72 h; or heated by microwaving (at 400 or 800 W) or boiling at 90 oC for 1, 5 or 10 min. Moreover, pickled (fermented) fish were divided into two groups: refrigerated at 4 oC (control) or frozen at -20 oC for 24 or 48 h. The infectivity of recovered metacercariae was confirmed by infecting hamsters with OV and then evaluating the recovery of adult worms after 1 month. We found that a heating process, by boiling or microwaving at 400 or 800 W for at least 5 min, could kill OV metacercariae, and freezing pickled fish at -20 oC for 48 h could kill OV metacercariae in all sizes of fish. The present study found that heating and freezing processes, as well as the fermentation process under optimal conditions, could kill OV metacercariae in a timely manner. This knowledge is valuable for implementation in endemic areas to control OV infection and cholangiocarcinoma.

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