Motility Of Intestinal Fluke, Echinostoma Spp, Metacercariae In Fish Dishes Prepared By Different Uncooked Methods

摘要

Fish-borne trematode is a worldwide problem. In addition to the major liver flukes, several types of intestinal flukes also use minnows as the intermediate host. Traditional ingestion of undercooked and uncooked fish preparations is a major factor in pathogen acquisition. Several freshly killed freshwater fish, Cyclocheilichthys armatus, were purchased from the local market and sent to the laboratory to be examined under a stereoscopic microscope for active Echinostoma spp metacercariae. A total of 10 fish were infected with many active metacercariae and used in the preparation of uncooked fish dishes: 1) left to dry at room temperature; 2) frozen; 3) refrigerated; 4) marinated in saline; and 5) marinated in 5% acetic acid solution. The motility of the metacercariae in each of these dishes was examined under a stereoscopic microscope. Motility was estimated as the level of activity or degeneration of the metacercariae at the start of the experiment and then every 30 minutes until all the parasites appeared degenerate (and therefore, presumably not viable). Degeneration of the parasites was slowed by cooling: degeneration of all metacercariae took approximately 10 hours in the refrigerated or frozen fish, compared with 4 hours in all other dishes left at room temperature. Of interest, this period is longer than reported times for the metacercariae of the intestinal flukes in recent published works. In conclusion, the studied uncooked preparation mimicking the traditional practice cannot induce degeneration to the contaminated metacercariae of in the short period. Since the real practice of the Thais is rapidly eating after preparation, hence, the active strategy to change this rooted behavior is necessary. Introduction Fish-borne trematode is a worldwide problem, with the number of people infected by liver flukes alone estimated at 21 million. In addition to the diseases caused by major liver flukes, O viverrini and C sinensis, infections by the other types of intestinal flukes such as Heterophyidae spp, Haplorchinae spp and Echinostoma spp are fished-borne diseases as well. Presently, these fluke diseases are a common public health problem in the northeastern region of Thailand.(1,2) Because the minnows are the source of the infective stage of these flukes, ingestion of undercooked and uncooked fish is a major factor in pathogen acquisition. Traditional Thai dishes such as Pla Som and Lab Pla are believed to be the source of infection to many people.(3) However, there have been only a few reports concerning the metacercariae in Thai traditional dishes. The first report was restricted to monitoring the viability of Haplorchis taichui metacercariae in only 2 specific dishes, Pla Som and Lab Pla.(4) The second and third report studied the viability of Heterophyidae spp and Haplorchinae spp metacercariae in matched minnows using a number of preparation methods.(5, 6) In order to fulfill the knowledge on the metacercariae study, the another study concerning the motility of Echinostoma spp metacercariae after different preparation methods that mimic traditional practices was performed. Materials and Methods Preparation of Uncooked Fish Dishes The protocol of this study is the same as the previous reports (5, 6). Several freshly killed freshwater fish, C armatus, were purchased from the local market and examined under a stereoscopic microscope for active Echinostoma spp metacercariae. The entire fish was examined, including the fins and flesh. A total of 10 fish were infected with many active metacercariae, in many parts. These infected fish were used further in the study. Five different raw fish dishes that mimicked traditional meals (2 fish/dish) were prepared using the following methods: 1) left to dry at room temperature (about 37 ° Celsius in Thailand) ; 2) frozen at -20° Celsius; 3) refrigerated at 4° Celsius; 4) marinated in saline (5% sodium chloride solution); and 5) marinated in 5% acetic acid solution to mimic traditional