The complete life cycle and developmental stages of the fluke, Metorchis ussuriensis sp. nov. (Trematoda, Platyhelminthes), are herein described. The results of the present experiments showed that, for flukes from the Primorsky Region in the Russian southern Far East, the first intermediate hosts are the snails Parafossarulus spiridonovi and Boreoelona ussuriensis, and the second intermediate hosts are freshwater fish, tadpoles, and snails. The definitive host in this experiment was Anas platyrhynchos dom. Morphometric parameters of M. ussuriensis sp. nov. demonstrate similarities with Metorchis taiwanensis, but the two species differ in the sizes of their bodies, sizes of suckers of adult worms, and sizes of cercariae, as well as respective positions of the finfold in cercariae. Phylogenetic reconstructions and genetic distances using the cox1 gene sequences support the conclusion that M. ussuriensis sp. nov. is well distinguished from all other species of the genus Metorchis, while sequences of internal transcribed spacers (ITS1 and ITS2) failed to separate M. ussuriensis sp. nov., Metorchis bilis, and Metorchis xanthosomus. In addition, we sequenced 1,402 bp of the 28SrRNA gene of M. ussuriensis sp. nov. being the first 28S sequences in the genus Metorchis. Comparison to other trematodes suggests that 28SrRNA could proof suitable for the differentiation of trematode species.
Domestic cats are a final host for some hepatic trematodes, and cat meat is used for human consumption in several parts of northern Vietnam. Since there is no tradition for commercial cat rearing in the area, cats are purchased alive from other areas as well, i.e., southern Vietnam and neighboring countries, and brought to slaughterhouses. This uncontrolled trade in live cats could pose a risk for spread of various parasites, including hepatic trematodes. Hence, in this study, we investigated the infections by hepatic trematodes in cats from the slaughterhouses. Cat livers were sampled from 12 slaughterhouses. Clonorchis sinensis and Platynosomum fastosum were found in 14 of 78 necropsied cats of local origin, while more than half of the non-local cats (170 of 318) were infected by C. sinensis, P. fastosum, or Opisthorchis viverrini. The non-local cats had higher prevalence (odds ratio = 6.61, P < 0.01, 95% CI: 2.34-19.41) and intensity of infection (count ratio = 6.47, P < 0.01, 95% CI: 1.77-23.59) by C. sinensis than local cats. Prevalence of P. fastosum infection did not differ significantly between the 2 groups of cats. Opisthorchis viverrini was found at low prevalence (2.5%) in non-local cats. The presence of O. viverrini in cats sampled in northern Vietnam and the high prevalence and intensity of infection in cats of non-local origin suggest that cats are transported over great distances, and this poses a risk of spreading these trematodes.
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