SBR- Content.pmd - INBO

4 - Biota of the Mekong BasinLiver fluke infection appears to be most common in Lao PDR, and theroute of infection is through the consumption of uncooked orinadequately cooked fish. The most common liver fluke parasite,Opisthorchis viverini, completes part of its life cycle inside a snail ofBithynia sp., associated with vegetation in still or slowly flowing waters.Within the tissues of the snail, the larvae reproduce asexually beforepassing out through the body wall as a free-swimming cercaria larvalstage. The cerciae burrow through the skin of a fish and then form acyst in the muscle. Should the muscle be ingested by a human, the cysthatches in the intestine and the fluke migrates up the host’s bile duct tothe liver, causing clinical disease. The eggs of the flukes pass out withthe host’s faeces, and if they enter water, they hatch as larvae thatsearch out snails to continue the life cycle. Cooking fish properly killsthe cysts, thus preventing infection. The infection is relatively easilytreated, but reinfection readily occurs, because hosts cannot developresistance.Fish species associated with Opisthorchis cysts at Nam NgumReservoir include Mystacoleucus sp. (pa langnam), Systomusorphoides (pa pok), Hampala dispar (pa sout) and Osteochilus haselti(pa eetai). All are fish common in the reservoir and are both consumedlocally and traded outside the immediate locality. Infections ofOpistorchis are easily treated, but reinfection is common if treatedindividuals are re-exposed.A photo of the Opisthorchisliver fluke35