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      Very low prevalence of Opisthorchis viverrini s.l. cercariae in Bithynia siamensis siamensis snails from the canal network system in the Bangkok Metropolitan Region, Thailand Translated title: Très faible prévalence des cercaires d’ Opisthorchis viverrini s.l. chez les mollusques Bithynia siamensis siamensis du réseau de canaux dans la région métropolitaine de Bangkok, Thaïlande

      1 , 1 , *

      Parasite

      EDP Sciences

      Prevalence, Cercarial infection, Liver fluke, Digenean larva, Intermediate host, Flowing-water habitat

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          Abstract

          The liver fluke Opisthorchis viverrini s.l. is associated with a long-term public health problem in Thailand. However, O. viverrini s.l. infection in Bithynia snails in the canal network system (CNS) in the Bangkok Metropolitan Region (BMR) has never been assessed. This study aimed to investigate the occurrence of B. siamensis siamensis and the prevalence of O. viverrini s.l. infection in this snail in the CNS in BMR along with morphological examination and molecular analyses on O. viverrini s.l. cercariae. The snails were randomly sampled from the CNS in all BMR areas from January 2018 to July 2019. Snail specimens were identified and examined for digenean infection by shedding and dissection. The cercariae were identified using morphology and molecular methods, including PCR with a species-specific primer and a Bayesian phylogenetic analysis of ITS2 sequences. Bithynia siamensis siamensis was found in almost all sampling localities, with different quantities and detected frequencies. From a total of 7473 B. s. siamensis specimens, O. viverrini s.l. infections were detected in the Northern Bangkok, Muang Nakhon Pathom, Krathum Baen, and Lam Luk Ka areas with an overall prevalence of 0.05% (4/7473) and prevalence of 0.22% (1/455), 0.21% (1/469), 0.40% (1/253), and 0.16% (1/614) in individual localities with positive snails, respectively. This study is the first investigation of digenean infection in the canal network system-type habitat in Thailand and revealed extremely low O. viverrini s.l. prevalence.

          Translated abstract

          La douve du foie Opisthorchis viverrini s.l. cause un problème de santé publique récurrent en Thaïlande. L’infection des Bithynia par O. viverrini s.l. dans le réseau de canaux (RC) dans la région métropolitaine de Bangkok (RMB) n’a jamais été évaluée. Cette étude visait à étudier la présence de B. siamensis siamensis et la prévalence de l’infection par O. viverrini s.l. chez ce mollusque dans le RC de la RMB, avec aussi une étude morphologique et des analyses moléculaires sur les cercaires d’ O. viverrini s.l. Les mollusques ont été prélevés au hasard dans le RC dans toutes les zones de la RMB de janvier 2018 à juillet 2019. Les spécimens de mollusques ont été identifiés et l’infection par les Digènes a été étudiée par excrétion et dissection. Les cercaires ont été identifiées à l’aide de méthodes morphologiques et moléculaires, y compris la PCR avec une amorce spécifique à l’espèce et une analyse phylogénétique bayésienne des séquences ITS2. Bithynia siamensis siamensis a été trouvé dans presque toutes les localités d’échantillonnage, avec des quantités et des fréquences de détection différentes. Sur un total de 7473 spécimens de B. s. siamensis, des infections par O. viverrini s.l. ont été détectées dans les régions du nord de Bangkok, Muang Nakhon Pathom, Krathum Baen et Lam Luk Ka avec une prévalence globale de 0,05 % (4/7473) et une prévalence respective de 0,22 % (1/455), 0,21 % (1/469), 0,40 % (1/253) et 0,16 % (1/614) dans les localités avec des mollusques positifs. Cette étude est la première enquête sur l’infection des Digènes dans l’habitat de type réseau de canaux en Thaïlande et a révélé une très faible prévalence d’ O. viverrini s.l.

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          Most cited references 66

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          How plasticity, genetic assimilation and cryptic genetic variation may contribute to adaptive radiations.

          There is increasing evidence that phenotypic plasticity can promote population divergence by facilitating phenotypic diversification and, eventually, genetic divergence. When a 'plastic' population colonizes a new habitat, it has the possibility to occupy multiple niches by expressing several distinct phenotypes. These initially reflect the population's plastic range but may later become genetically fixed by selection via the process of 'genetic assimilation' (GA). Through this process multiple specialized sister lineages can arise that share a common plastic ancestor - the 'flexible stem'. Here, we review possible molecular mechanisms through which natural selection could fix an initially plastic trait during GA. These mechanisms could also explain how GA may contribute to cryptic genetic variation that can subsequently be coopted into other phenotypes or traits, but also lead to nonadaptive responses. We outline the predicted patterns of genetic and transcriptional divergence accompanying flexible stem radiations. The analysis of such patterns of (retained) adaptive and nonadaptive plastic responses within and across radiating lineages can inform on the state of ongoing GA. We conclude that, depending on the stability of the environment, the molecular architecture underlying plastic traits can facilitate diversification, followed by fixation and consolidation of an adaptive phenotype and degeneration of nonadaptive ones. Additionally, the process of GA may increase the cryptic genetic variation of populations, which on one hand may serve as substrate for evolution, but on another may be responsible for nonadaptive responses that consolidate local allopatry and thus reproductive isolation.
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            Taxonomy and biology of liver flukes.

            Opisthorchis viverrini is a human liver fluke endemic in Thailand, Lao PDR and Cambodia. Three subspecies of Bithynia siamensis and 18 species of cyprinoid fish are susceptible first and second intermediate hosts, respectively. The differentiation between the adult worm of O. viverrini and that of the closely related species, Opisthorchis felineus and Clonorchis sinensis, is mainly based on the shape and position of the testes and the arrangement of the vitellaria. Eggs of these flukes are morphologically similar and problematic in identification. However, the differentiation between opisthorchid and lecithodendrid eggs is possible. Morphology and biology of each stage are comparatively reviewed. Biological aspects of snail and fish hosts are also included.
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              The non-marine aquatic mollusca of Thailand

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                Author and article information

                Journal
                Parasite
                Parasite
                parasite
                Parasite
                EDP Sciences
                1252-607X
                1776-1042
                2021
                08 January 2021
                : 28
                : ( publisher-idID: parasite/2021/01 )
                Affiliations
                Animal Systematics and Ecology Speciality Research Unit, Department of Zoology, Faculty of Science, Kasetsart University Bang Khen Campus 10900 Bangkok Thailand
                Author notes
                [* ]Corresponding author: fsciwyp@ 123456ku.ac.th
                Article
                parasite200107 10.1051/parasite/2020072
                10.1051/parasite/2020072
                7792506
                33416490
                © P. Rachprakhon & W. Purivirojkul, published by EDP Sciences, 2021

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                Page count
                Figures: 5, Tables: 4, Equations: 0, References: 64, Pages: 12
                Categories
                Research Article

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