Human Opisthorchis and Haplorchis infections in Laos

A study of the epidemiology of trematode infections was carried out in Vientiane province, Laos, comprising examination of snails, fish, cats, and human stools. Opisthorchis viverrini cercariae were found in the snail Bithynia siamensis goniomphalus (Bithyniidae) and Haplorchis taichui cercariae in Tarebia granifera (Thiaridae). O. viverrini metacercariae were recorded in the flesh of 7 species of cyprinid fish; metacercariae of the heterophyid fluke Haplorchis taichui were found in 4 species of cyprinid fish and those of H. pumilio in 2 species. Cats from the same localities were infected with O. viverrini and 4 species of heterophyid flukes, frequently as multiple infections. The highest prevalence of small fluke eggs in human stools was recorded in the 20-29 years age group, particularly in males (90.4%). Three-quarters of human infections were light (less than 1000 eggs/g), the highest value (2975 eggs/g) being recorded in the 10-14 years age group. Identification of small flukes excreted by Laotian patients after treatment with praziquantel in Czechoslovakia revealed more cases with H. taichui than with O. viverrini. The results confirmed the simultaneous occurrence of O. viverrini and intestinal heterophyid flukes in the area studied.