ISSN 0859-290X, Vol. 6, No. 3 – March 2001

By Jorgen G. Jensen and Dr. Kathleen I. Matics

An FAO study finds that more than 50% of villagers near the Nam Ngum Reservoir in the Lao PDR are infected with the Liver Fluke, a parasite causing severe illnesses.

174 villagers living close to the Nam Ngum Reservoir were examined for parasites in a recent study carried out by F AO in collaboration with the Lao Department of Live- stock and Fisheries and the Centre for Malariology, Parasitology and Entomology (CMPE) in Vientiane. 74% were infected with parasites, and of these, 52% with the liver fluke (Opisthorchis viverini). A few more fish-borne parasites were found among the total 12 parasites identified through faecal analyses. This is considered relatively high compared with other records in the Lao PDR. The high incidence is closely related to the reservoir and the habits of eating raw fish.

Through Snails and Fish to Humans The adult liver fluke is a 7-12 mm long "trematode" (see the photo be- low left) living inside the liver in the biliary tree of man, where it produces eggs. The eggs are passed in the faeces. When ingested by a particular snail of the genus Bithynia, which lives in the reservoirs, the eggs hatch and the second stage of the parasite, the "miracidia" is born in the snail. The parasites go through another stage before they develop into free swimming "cercariae", tiny small organisms, which leave the snails and enter the freshwater fish beneath the scales. They incapsulate themselves in the muscle tissue of the fish as tiny metacercarial cysts (see the photo at right). When the fish is then eaten by people, raw or not sufficiently cooked, the cysts get into the small intestine and migrate up the bile duct. The cycle is then complete, and the liver fluke develops in the liver, resulting in a clinical disease, and is often seen in association with liver malfunction or degeration, infected pancreas and intestinal cancer. Thus the liver fluke can cause very serious illness, which may be fatal. Many fish species from the reservoir carry the parasites. The study checked the market at village Talad nearby and found four different species or species groups of that carried them. These comprised the Mystacoleucus sp. (Pa langnam), Syslomus orphoides (Pa pok), dispar (Pa soul) and Osleochilus hasselli (Pa eelai), all common fish in the reservoir. In December 1999 fish from the market in Vientiane had been checked, and samples of both Pa pok and Pa soul were found to contain metacercariae of the liver fluke.

Still Water Makes It Happen It is the still water in the reservoir that makes possible the passage of the parasites from humans to snail to fish and back to humans. It is therefore also a potential problem in aquaculture, as described by Pedro Bueno in Catch and Culture in May 1998. After correct diagnosis, appropriate treatment can easily be performed. However, re-infection may take Adult liver fluke called place rather quickly if other measures are not taken simultaneously. In 1995, an outbreak of parasitic lives in bile ducts and produce pathological infection was reported in the same village. At that time the people were treated with anti-parasitic drugs changes. Actual size: 7-12 mm with a success rate of 90-95%. However, four years later, over half of the persons tested were again infected by the liver flukes. Single mass treatment is short-lived and repeated treatment at periodic intervals may be necessary in combination with other changes.

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Stop Eating Raw Fish First of all, food habits have to be changed. The consumption of raw or semi-cooked freshwater fish will have to be abolished. But old habits die hard, and it may not happen without a strong awareness and in- formation campaign. Moreover, processing methods should be checked and safe practices adhered to, as Pedro Bueno in his article re- ports that metacercariae of certain parasites may survive for months in frozen fish and for days or even weeks in salted and dried products depending on the type of processing. The Study Team recommends that more attention be given to the parasitic diseases through training of local health officers in the area around the Nam Ngum Reservoir, and training of personnel who can carry out the identification of the parasites. In the long-term, health education and sanitary upgrading are essential to prevent re-infection.

Systomus orphoides (Valenciennes, 1842), an

intermediary of the liver luke.

References Bueno, P ., Assuring the Safety of Aquaculture Food Products, Catch and Culture, Vol. 3, No.4, May 1998, pp. 6-8. Manson-Bahr, P.E.C. and Bell, D.R. Manson's Tropical Diseases, 19th Edition (Bailliere Tindall, London, 1987). Peters, W., and Giles, Herbert M. A Colour Atlas of Tropical Medicine & Parasitology, 3rd Edition (Wolfe Medical Publications Ltd., London 1989), pp. 115-118. Sithithawarn, Paibaan, Elkins, David B. and Smam Tesana, eds. A Training Course on Water-borne Diseases in the Basin (Khan Kaen University, Khan Kaen, 1990), pp. 57-61. Sithithawom, Paiboon and Keturat Sukhavat, Improved Utilization, Quality and Safety of Fish and Fisheries Products (Technical Cooperation Programme, Lao PDR, FAO, TCP/LAO/8823 Field Document No.5, Bangkok, January 2000,5 pp.)

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