1:45 PM - 3:15 PM
[HCG25-P03] Importance of Freshwater Fish Fisheries Environmental Survey: for conducting effective survey on Opisthorchis viverrinia in Cambodia
Keywords:Opisthorchis viverrini, Enivironment of fishing points, Raw freshwater fish consumption
[Background]: One of liver flukes, Opisthorchis viverrini, hereafter (Ov) infection is transmitted to humans and other mammals by raw consumption of freshwater carp (the second intermediate host) infected by the larvae (metacercariae). The cercariae grow in the first intermediate host, snails (Bithynia sp.), and swim in the water to parasitise the freshwater fish (Fig. 1). Ov infections have the characteristics of both a food-borne parasitic infection and a waterborne infection. It is an important public health issue as it causes liver cancer and is the subject of national health measures in Thailand and Lao PDR.
[Endemic situation of Ov infection in Cambodia]: Ov endemic areas were specifically identified in Cambodia in 2006, based on epidemiological surveys conducted by us. 14 provinces have been indicated to have endemic areas (>20% EPR) or infected areas (<20% EPR) in the survey until 2019 in Cambodia. However, the surveyed areas have been limited to only a few regions in each province, and the prevalence of the country were remained to be clarified.
[Why is it necessary to conduct environmental surveys of fishing points? ] In the case of Kampong Cham Province, where we conducted our survey, the characteristics of the endemic area are as follows: 1) residents who fish in the mainstream of the Mekong River have low EPRs (e.g., the freshwater fish consumption rates were nearly 100% among them, but the EPRs were only a few per cent). 2) many ponds and lakes are flooded during the rainy season, and many endemic villages have been observed in these flooded areas; 3) endemics have also been observed in areas where paddy fields are used as fishing points during the rainy season; and 4) even if the raw freshwater consumption rates were high, EPR of several neighbouring villages have mixed of more than 20% and 0 to a few percents. That is, it is difficult to find endemic areas even if the survey targets the area around the main stream of the Mekong River, and it is necessary to conduct surveys in all areas of the country, including the countless ponds, swamps and rice paddies that are used as fishing points. In addition, even if one endemic village exists, it does not mean that there are also endemic villages in the surrounding area, making it difficult to ascertain the endemic situation through sampling surveys, but it is close to impossible to conduct a survey of all households, both in terms of budget and in terms of survey efficiency.
An efficient selection of fishing points inhabited by freshwater fish that provide a route of infection is necessary in order to prioritise the myriad of potential survey sites. Clarification of the environmental factors of these fishing grounds and the conditions of fishing points where the first and second intermediate hosts are likely to come into contact is expected to facilitate efficient surveys and contribute to progress in the fight against Ov infections in Cambodia.
[Endemic situation of Ov infection in Cambodia]: Ov endemic areas were specifically identified in Cambodia in 2006, based on epidemiological surveys conducted by us. 14 provinces have been indicated to have endemic areas (>20% EPR) or infected areas (<20% EPR) in the survey until 2019 in Cambodia. However, the surveyed areas have been limited to only a few regions in each province, and the prevalence of the country were remained to be clarified.
[Why is it necessary to conduct environmental surveys of fishing points? ] In the case of Kampong Cham Province, where we conducted our survey, the characteristics of the endemic area are as follows: 1) residents who fish in the mainstream of the Mekong River have low EPRs (e.g., the freshwater fish consumption rates were nearly 100% among them, but the EPRs were only a few per cent). 2) many ponds and lakes are flooded during the rainy season, and many endemic villages have been observed in these flooded areas; 3) endemics have also been observed in areas where paddy fields are used as fishing points during the rainy season; and 4) even if the raw freshwater consumption rates were high, EPR of several neighbouring villages have mixed of more than 20% and 0 to a few percents. That is, it is difficult to find endemic areas even if the survey targets the area around the main stream of the Mekong River, and it is necessary to conduct surveys in all areas of the country, including the countless ponds, swamps and rice paddies that are used as fishing points. In addition, even if one endemic village exists, it does not mean that there are also endemic villages in the surrounding area, making it difficult to ascertain the endemic situation through sampling surveys, but it is close to impossible to conduct a survey of all households, both in terms of budget and in terms of survey efficiency.
An efficient selection of fishing points inhabited by freshwater fish that provide a route of infection is necessary in order to prioritise the myriad of potential survey sites. Clarification of the environmental factors of these fishing grounds and the conditions of fishing points where the first and second intermediate hosts are likely to come into contact is expected to facilitate efficient surveys and contribute to progress in the fight against Ov infections in Cambodia.