Schistosoma mekongi is primarily a parasite of dogs and rodents. This parasite has been known to exist in the lower Mekong River Basin since 1957. The worm occurs in Cambodia, Thailand and Laos. The adult worms are situated in the intestinal blood vessels in the branches that open into the superior mesenteric vein and the portal vein. The eggs resemble those of S. japonicum, but are somewhat smaller and rounder (subspherical, size range 30 to 55 µm by 50 to 65 µm, with a small lateral spine near one end which is rather difficult to see). The miracidia infect the aquatic snail Lithoglyphopsis aperta. Most light infections in humans are asymptomatic, but ectopic localisations can result in severe morbidity (incl. neurological lesions). Hepatosplenomegaly with diverted blood circulation occurs in heavy infections. Kato-Katz thick smears are simple and sensitive quantitation technique. The zinc sulfate concentration technique is not recommended (eggs will rupture). The formalin-ethyl acetate technique is better.