Free-grazing ducks play a major role in the rural economy of Eastern Asia in the form of egg and meat production. In Thailand, the geographical location, tropical climate conditions and wetland areas of the country are suitable for their husbandry. These environmental factors also favor growth, multiplication, development, survival, and spread of duck parasites. In this study, a total of 90 free-grazing ducks from northern, central, and northeastern regions of Thailand were examined for intestinal helminth parasites, with special emphasis on zoonotic echinostomes. Of these, 51 (56.7%) were infected by one or more species of zoonotic echinostomes, Echinostoma revolutum, Echinoparyphium recurvatum, and Hypoderaeum conoideum. Echinostomes found were identified using morphological criteria when possible. ITS2 sequences were used to identify juvenile and incomplete worms. The prevalence of infection was relatively high in each region, namely, north, central, and northeast region was 63.2%, 54.5%, and 55.3%, respectively. The intensity of infection ranged up to 49 worms/infected duck. Free-grazing ducks clearly play an important role in the life cycle maintenance, spread, and transmission of these medically important echinostomes in Thailand.
Animals ; Bird Diseases/*epidemiology/*parasitology ; DNA, Ribosomal Spacer/chemistry/genetics ; Ducks/*parasitology ; Echinostomatidae/anatomy & histology/classification/genetics/*isolation & purification ; Helminthiasis/epidemiology/parasitology ; Intestinal Diseases/epidemiology/parasitology/*veterinary ; Microscopy ; Prevalence ; Sequence Analysis, DNA ; Thailand ; Trematode Infections/epidemiology/parasitology/*veterinary

Objective: To explore genetic variations of Hypoderaeum conoideum collected from domestic ducks from 12 different localities in Thailand and Lao PDR, as well as their phylogenetic relationship with American and European isolates. Methods: The nucleotide sequences of their nuclear ribosomal DNA (ITS), mitochondrial cytochrome c oxidase subunit 1 (CO1), and NADH dehydrogenase subunit 1 (ND1) were used to analyze genetic diversity indices. Results: We found relatively high levels of nucleotide polymorphism in ND1 (4.02%), whereas moderate and low levels were observed in CO1 (2.11%) and ITS (0.96%), respectively. Based on these polymorphisms, the 20 ND1, 12 CO1, and 18 ITS haplotypes were classified, and several common haplotypes were observed in all samples. At least three major lineages, namely American, European and Asian lineages, have been classified by phylogenetic analyses based on ND1 sequences. Conclusions: Our report demonstrates that the ND1 gene is the most suitable genetic marker to explore genetic variation and phylogenetic relationship of Hypoderaeum conoideum. However, a combination of all loci for ND1, CO1 and ITS would be of great value toward further genetic investigation of this endemic worldwide parasite. Thus, comprehensive molecular genetic analyses of Hypoderaeum conoideum from its worldwide distribution is needed to further understanding of the evolutionary and systematic relationships of this parasite.