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.

Seroprevalence of Toxoplasma gondii in free range chickens (Gallus domesticus) in Khon Kaen province, Thailand.

Toxoplasmosis is caused by the infective stage of Toxoplasma gondii and is often acquired from contaminated food and water. Data on the prevalence of T. gondii in freerange chickens (Gallus domesticus) in Khon Kaen province, Northeast Thailand, are limited. A total of 257 serum samples were collected and antibodies to T. gondii were examined by the latex agglutination test; 26 (10.1%) free-range chickens were positive. By logistic regression, the seroprevalence rate was 3.8 fold higher in the rainy season compared to the dry season (OR=3.81, 95% CI=1.39-10.47, P=0.006). The mean rainfall in the seropositive group (3.48 ± 2.05 mm) was significantly higher (P=0.028) compared to the seronegative group (2.42 ± 2.35 mm). The point biserial correlation coefficients showed a positive association between seropositivity and mean rainfall (r=0.137, P=0.028) but no significant associations for temperature or humidity. In conclusion, the presence of T. gondii infection in free-range chickens in Khon Kaen province suggests environmental contamination. The wet season and mean rainfall are significant associations with seroprevalence. The prevention of faecal contamination from cats to the environment is a good strategy to reduce the risk of infection in soil feeding animal such as chicken.

Trematode diversity in the freshwater snail Bithynia siamensis goniomphalos sensu lato from Thailand and Lao PDR.

In order to obtain a comprehensive understanding of trematode diversity in Bithynia siamensis goniomphalos sensu lato, the first intermediate host of the liver fluke Opisthorchis viverrini s.l., the prevalence of larval trematode species was investigated in different localities in Thailand and Lao People's Democratic Republic (Lao PDR). In Thailand, snail samples were collected from 29 localities in the nine provinces: Buri Ram, Surin, Chaiya Phum, Maha Sarakham, Khon Kaen, Kalasin, Mukdahan, Sakon Nakhon and Nakhon Phanom. In Lao PDR, snail samples were collected from 21 localities in Vientiane Province and six localities in Savannakhet Province. Snails were identified by standard morphological criteria and then examined for trematode infection using the cercarial shedding method. Twenty different types of cercariae were detected and identified, based on morphological criteria. Virgulate type 1 emerged as the most common cercaria, with an average prevalence of 10.90% (range 0.26-54.22%) in Thailand and 6.58% (range 1.15-89.77%) in Lao PDR. Opisthorchis viverrini s.l. cercariae were the fourth most common in Thailand, with an average prevalence of 1.59% (0.15-6.93), while in Lao PDR their prevalence was 0.96% (0.08-8.37). The high diversity of trematode cercariae observed in this study indicates that B. s. goniomphalos s.l. is highly susceptible to infection with a variety of trematode species. However, the role of non-opisthorchiid trematodes as fish-borne parasites in human health is not fully known and further molecular identification is required.