Preliminary genetic evidence of two different populations of Opisthorchis viverrini in Lao PDR

Opisthorchis viverrini is a major public health concern in Southeast Asia. Various reports have suggested that this parasite may represent a species complex, with genetic structure in the region perhaps being dictated by geographical factors and different species of intermediate hosts. We used four microsatellite loci to analyze O. viverrini adult worms originating from six species of cyprinid fish in Thailand and Lao PDR. Two distinct O. viverrini populations were observed. In Ban Phai, Thailand, only one subgroup occurred, hosted by two different fish species. Both subgroups occurred in fish from That Luang, Lao PDR, but were represented to very different degrees among the fish hosts there. Our data suggest that, although geographical separation is more important than fish host specificity in influencing genetic structure, it is possible that two species of Opisthorchis, with little interbreeding, are present near Vientiane in Lao PDR

Seasonal cercarial emergence patterns of Opisthorchis viverrini infecting Bithynia siamensis goniomphalos from Vientiane Province, Lao PDR

Background Snail intermediate hosts play a pivotal role in maintaining the life cycles of trematodes, including Opisthorchis viverrini. We investigated the emergence patterns of O. viverrini cercariae infecting Bithynia siamensis goniomphalos at foci in an endemic area in Vientiane Province, Lao PDR. Findings Samples of B. s. goniomphalos collected during the hot-dry, rainy and cool-dry seasons were examined for O. viverrini infection by cercarial shedding. Emergence of cercariae from O. viverrini-positive snails was monitored daily from 06:00–18:00 h for seven consecutive days at 2 hourly intervals. Snail infections varied seasonally, being highest in the cool-dry season. Peak cercarial emergence was not consistent in different seasons, occurring between 08.00–10.00 h during the hot-dry season and between 12.00–14.00 h during the rainy and cool-dry seasons. The cercarial output was highest in the hot-dry season. The prevalence of infection and the emergence of cercariae were strongly dependent on snail size. Conclusions This study shows that size of snails and environmental factors (such as season) may affect the emergence patterns of cercariae of O. viverrini in snails. These results have both fundamental and applied implications for opisthorchiasis epidemiology and control

Phylogenetic relationships within the Opisthorchis viverrini species complex with specific analysis of O. viverrini sensu lato from Sakon Nakhon, Thailand by mitochondrial and nuclear DNA sequencing

The liver fluke Opisthorchis viverrini sensu lato causes serious public-health problems in Northeast Thailand and Southeast Asian countries. A hypothesis has been proposed that O. viverrini represents a species complex with varying levels of genetic differentiation in Thailand and Lao PDR. This study aimed to clarify whether O. viverrini populations can be genetically divided into separate taxa. We collected O. viverrini s.l. from eight different locations in Lao PDR and Thailand. The results of nad1, cox1, CF-int6, Pm-int9, ITS2 and 28S rDNA sequence analysis revealed that sub-structuring occurred between the eight populations. We found that O. viverrini s.l. from Sakon Nakhon (SK), Thailand, shows significant genetic differentiation (P < .05) from all other isolates from different localities in Thailand and Lao PDR. This was supported by haplotype and phylogenetic tree analyses in which the SK isolate was separated from all other isolates. This suggests that O. viverrini s.l. from SK is a cryptic species. The data, however, also confirm the association between genetic groups of O. viverrini s.l. and specific wetland systems, and raise important questions regarding the epidemiological significance of these genetic differences

Molecular identification of trematode parasites infecting the freshwater snail Bithynia siamensis goniomphalos in Thailand

Digenetic trematodes are important parasites of humans and animals. They have complex life cycles and typically infect a gastropod as the first intermediate host. Bithynia siamensis goniomphalos, the first intermediate host of the liver fluke, Opisthorchis viverrini, harbours a wide variety of other trematode species. Morphological details of cercariae of 20 trematode taxa from B. s. goniomphalos, collected mainly in Thailand from 2009 to 2014, were provided in an earlier paper. Correct identification to the species or genus level based on morphology of these cercariae is generally not possible. Therefore, we used molecular data to improve identification and to investigate the diversity of the species of trematodes infecting B. s. goniomphalos. We were successful in extracting, amplifying and sequencing portions of the 28S ribosomal RNA (rRNA) gene for 19 of these 20 types of cercaria, and the internal transcribed spacer 2 region for 18 types. BLAST searches in GenBank and phylogenetic trees inferred from the 28S rRNA sequences identified members of at least nine superfamilies and 12 families. Only a few cercariae could be assigned confidently to genus or species on the basis of the sequence data. Matching sequence data from named adult trematodes will be required for definitive identification. There is clearly a great diversity of trematode species utilizing B. s. goniomphalos in Thailand

The ecology of the Bithynia first intermediate hosts of Opisthorchis viverrini

10.1016/j.parint.2011.07.019Parasitology International61138-45PAIN