First morphological and molecular identification of third-stage larvae of Anisakis typica (Nematoda: Anisakidae) from marine fishes in Vietnamese water.

Anisakid nematodes are parasites of cetaceans, their larval stages live in marine fishes. The third-stage larvae of some Anisakis species are also the etiological agents of human anisakiasis caused by consumption of raw or undercooked infected fish. Thus, identification of Anisakis larvae at the species level is crucial for their ecology and epidemiology. In Vietnam, although Anisakis larvae have been reported, they have not been identified to the species level. The aim of this study was, therefore, to identify third-stage larvae of Anisakis collected from marine fishes in Vietnamese water, based on morphological characteristics and molecular analysis. All Anisakis larvae found in this study were morphologically similar to each other and identical to Anisakis typica. In addition, molecular analysis based on ITS1-5.8S-ITS2 sequences confirmed them as A. typica. Vietnamese A. typica population was genetically close to those from Asian countries and Australia. The third-stage larvae of A. typica were collected from eight fish species from three localities in the South of Vietnam. Among them, seven were recorded as new intermediate hosts of A. typica. This is the first identification of A. typica larvae in Vietnamese water with records of new fish hosts.

A new myxosporean species, Henneguya lata n. sp. (Myxozoa: Myxobolidae), from the gills of yellowfin seabream Acanthopagrus latus (Perciformes: Sparidae) in the Gulf of Tonkin, Vietnam.

During a survey of myxosporean parasites of marine fish in the coastal region of Vietnam, a species of the genus Henneguya (Myxosporea: Bivalvulida) was found in the gill of yellowfin seabream Acanthopagrus latus (Perciformes: Sparidae). White and oval cysts, measuring 145-220 µm in diameter, were detected in the gill lamellae of 4 of 15 fish examined (26.7%). Mature myxospores were elongate, with smooth valves, two similar polar capsules, and having the following dimensions: spore body length 9.9 ± 0.5 (8.9-12.5) µm, body width 6.7 ± 0.3 (6.1-7.6) µm, thickness 5.1 ± 0.2 (4.8-5.4) µm, caudal appendage length 10.0 ± 1 (8.3-11.6) µm, and total myxospore length 19.3 ± 1.4 (16.5-21.5) µm. The polar capsules were ovoid, measuring 3.2 ± 0.2 (2.8-3.9) µm long and 1.9 ± 0.2 (1.5-2.3) µm wide. Each polar capsule has a polar filament with 4-5 coils. Histological analysis revealed plasmodia in the connective tissues of the gill lamellae, but inflammation and deformation of the gills were not observed. In the phylogenetic tree reconstructed from the small subunit ribosomal DNA (SSU rDNA), sequences of the Henneguya specimens found in this study form a distinct branch. Morphological characteristics and molecular data identified a new species, namely Henneguya lata n. sp.

Paragonimus heterotremus Chen et Hsia, 1964 (Digenea: Paragonimidae): species identification based on the biological and genetic criteria, and pathology of infection.

As a result of the experimental infection of rats with metacercariae of Paragonimus heterotremus Chen et Hsia, 1964 from crabs (Potamiscus tannanti) caught in Yen Bai province, Vietnam, it was found that worms migrated into the lungs, to the liver and less frequently to the tissue that lines body cavities of the hosts, where they reached the adult stage, but in the muscles, worms stayed at the larval stage. Studies have shown that for P. heterotremus, rats can simultaneously play the role of the final and paratenic host; herewith, an infection with the trematode of this species can lead to the development of three forms of paragonimiasis: pulmonary, hepatic and muscular. Eggs from the adult worms localised in the liver, unlike eggs from the adult worms localised in the lungs, were not excreted into the external environment, but accumulated inside the organ. Histology and description of changes, which take place on the external surface of organs affected with P. heterotremus, are given in this study. Based on the behavioural characteristics of worms during rat infection and molecular genetic data, we established that worms from Vietnam and India should be assigned to different species of Paragonimus. P. heterotremus distribution is limited to the territory of the Southeast China, Northern Vietnam, Laos and Thailand.

Developmental stages of Notocotylus magniovatus Yamaguti, 1934, Catatropis vietnamensis n. sp., Pseudocatatropis dvoryadkini n. sp., and phylogenetic relationships of Notocotylidae Lühe, 1909.

Data on the life cycles and morphology of the developmental stages of Notocotylus magniovatus, Catatropis vietnamensis n. sp., and Pseudocatatropis dvoryadkini n. sp. were obtained. The Pseudocatatropis genus was restored based on our results. For the studied trematodes, the snails Parajuga spp., Helicorbis sujfunensis (Russia), and Melanoides tuberculata (Vietnam) serve as first intermediate hosts. It has been established that C. vietnamensis n. sp. differs from Catatropis harwoodi and Catatropis pakistanensis in the length of the ridge and metraterm and the location of the anterior papillae. In the life cycle of P. dvoryadkini n. sp., as in Pseudocatatropis joyeuxi, cercariae do not leave the first intermediate host. Both species are very similar in morphometric features, despite the fact that they share no common first intermediate hosts in their life cycles, and the areas of the European and Asian populations of flukes do not overlap. In phylogenetic trees and genetic distances based on the nucleotide sequences of the 28S gene and the ITS2 region of ribosomal DNA, Notocotylus attenuatus, Notocotylus intestinalis, and Notocotylus magniovatus are combined into one systematic group, while C. vietnamensis n. sp. and Catatropis indicus form another group. A third group includes members of different genera: P. dvoryadkini n. sp., and Notocotylus malhamensis, as well as three unclassified Notocotylus spp. The presence in the last group of flukes with three rows of papillae and a median ridge and lateral papillae indicates that these systematic criteria are not determinant in establishing membership of the parasitic worms to one or another genus of Notocotylidae.

Descriptions of acanthocephalans, Cathayacanthus spinitruncatus (Rhadinorhynchidae) male and Pararhadinorhynchus magnus n. sp. (Diplosentidae), from marine fish of Vietnam, with notes on Heterosentis holospinus (Arhythmacanthidae).

Males of Cathayacanthus spinitruncatus Amin, Heckmann & Ha, 2014 (Rhadinorhynchinae Lühe, 1912) are described for the first time from Leiognathus equulus in Hai Phong and Nha Trang and from pony fish Nuchequula flavaxilla in Quang Ninh in the Pacific waters of Vietnam. The male allotype status is designated. Males of C. spinitruncatus are smaller and have fewer and smaller proboscis hooks and trunk spines than females. The male reproductive structures are in the posterior fifth of the trunk and with 6 club-shaped cement glands gradually merging into 6 independent cement gland ducts. The proboscis receptacle is more than half as long as the trunk and with a cephalic ganglion at its anterior end. In females, the receptacle is only about one fifth the length of the trunk. Specimens described as Cathayacanthus bagarii Moravec & Sey, 1989 were shown to have been wrongly assigned to Cathayacanthus. Pararhadinorhynchus magnus n. sp. (Diplosentidae) is described from Scatophagus argus off Hai Phong in the Gulf of Tonkin. It is the third species of the genus and is readily distinguished from the Australian species by having a considerably larger trunk and male reproductive structures, and more proboscis hooks. X-ray microanalysis (EDAX) of intact and gallium-cut hooks of P. magnus showed high calcium and phosphate mainly in the central core. Specimens of Heterosentis holospinus Amin, Heckmann & Ha, 2011 (Arhythmacanthidae) are also reported from L. equulus off Quang Binh, new host and locality records.

Genetic diversity of the Chinese liver fluke Clonorchis sinensis from Russia and Vietnam.

Clonorchiasis is a parasitic disease of high public health importance in many countries in southeastern Asia and is caused by the Chinese liver fluke Clonorchis sinensis. However, the genetic structure and demographic history of its populations has not been sufficiently studied throughout the geographic range of the species and available data are based mainly on partial gene sequencing. In this study, we explored the genetic diversity of the complete 1560 bp cytochrome c oxidase subunit 1 (cox1) gene sequence for geographically isolated C. sinensis populations in Russia and Vietnam, to our knowledge for the first time. The results demonstrated low nucleotide and high haplotype differentiation within and between the two compared regions and a clear geographical vector for the distribution of genetic diversity patterns among the studied populations. These results suggest a deep local adaptation of the parasite to its environment including intermediate hosts and the existence of gene flow across the species' range. Additionally, we have predicted an amino acid substitution in the functional site of the COX1 protein among the Vietnamese populations, which were reported to be difficult to treat with praziquantel. The haplotype networks consisted of several region-specific phylogenetic lineages, the formation of which could have occurred during the most extensive penultimate glaciations in the Pleistocene Epoch. The patterns of genetic diversity and demographics are consistent with population growth of the liver fluke in the late Pleistocene following the Last Glacial Maximum, indicating the lack of a population bottleneck during the recent past in the species' history. The data obtained have important implications for understanding the phylogeography of C. sinensis, its host-parasite interactions, the ability of this parasite to evolve drug resistance, and the epidemiology of clonorchiasis under global climate change.

[On the fauna of trematodes from the family Dicrocoeliidae (Plagiorchidida) parasitizing animals in Vietnam].

A review of the fauna of trematodes from the family Dicrocoeliidae parasitizing animals in Vietnam has been conducted. According to original and literature data, 57 trematode species from 15 genera were recorded. Data on hosts, localization, and distribution of all these species in the territory of Vietnam are given.