Complicated epidemiology of small liver tape-worm disease caused by Opisthorchis viverrini species in central area, Viet Nam due to occurrence of Opisthorchis sp. BD2013 species caused disease in duck

Abstract

The cross sectional studies at the epidemiological area in Binh Dinh province was conducted to
define the prevalence and risk factors of the small liver tape-worm disease caused by O. viverrini
species in both last hosts, such as: human and duck, and the intermediate hosts, such as: snail
and fish. In addition, the gene sequence in mitochondrial of the identified small liver tape-worms
was decoded in order to define the genetic position of this small liver tape-worm species in the
phylogenetic tree of the Opisthorchiidae family in relationship with the Opisthorchis species in this
family that was identified prior. The studied result showed that the infection rate of human with O.
viverrini in the surveyed communities in Binh Dinh province was 11.4% and the infection rate of
duck with Opisthorchis sp BD 2013 was 34.3%. The two snail species, such as: Bithynia siamensis  goniomphalos and B. funiculata were determined to be the first intermediate hosts and 10 fresh water
fish species, belonging to Cyprinidae family were determined to be the second intermediate hosts of
the small liver tape-worm (O. viverrini) in Viet Nam. Of which, the infection rate of Carassius auratus
species with (the raw meat of this fish species was often eaten by the communities in the surveyed
region) O. viverrini was highest. Also, the studied result indicated that O. viverrini and Opisthorchis sp
BD2013 were identified in the same 1st intermediate host (snail species: Bithynia funiculata) and 2nd
and 3rd intermediate hosts (fish species: Esomus metallicus, Puntius brevis and Rasbora aurotaenia).
The result of analysing genes (nad1, cob and cox1) in mitochondrial and phylogenetic tree indicated
that Opisthorchis sp BD2013 was an independent small tape-worm species, it related closely to O.
viverrini. Although, the Opisthorchis sp BD2013 species was not found in human, but the sympatric
distribution and sharing the same intermediate hosts in the same epidemiological area of these small
liver tape-worm species indicated that the risk of creating a complicated epidemiology of the small
liver tape-worm infection due to crossing and gene transfer between two closely relation small liver
tape-worm species may occur in the same last host.