Genetic characterization of Echinostoma revolutum and Echinoparyphium recurvatum (Trematoda: Echinostomatidae) in Thailand and phylogenetic relationships with other isolates inferred by ITS1 sequence

Abstract

Echinostomatidae are common, widely distributed intestinal parasites causing significant disease in both animals and humans worldwide. In spite of their importance, the taxonomy of these echinostomes is still controversial. The taxonomic status of two species, Echinostoma revolutum and Echinoparyphium recurvatum, which commonly infect poultry and other birds, as well as human, is problematical. Previous phylogenetic analyses of Southeast Asian strains indicate that these species cluster as sister taxa. In the present study, the first internal transcribed spacer (ITS1) sequence was used for genetic characterization and to examine the phylogenetic relationships between an isolate from Thailand with other isolates available from GenBank database. Interspecies differences in ITS1 sequence between E. revolutum and E. recurvatum were detected at 6 (3%) of the 203 alignment positions. Of these, nucleotide deletion at positions 25, 26, and 27, pyrimidine transition at 50, 189, and pyrimidine transversion at 118 were observed. Phylogenetic analysis revealed that E. recurvatum from Thailand clustered as a sister taxa with E. revolutum and not with other members of the genus Echinoparyphium. Interestingly, this result confirms a previous report based on allozyme electrophoresis and mitochondrial DNA that E. revolutum and E. recurvatum in Southeast Asia are sister species. Hence, the taxonomic status of E. recurvatum in Thailand, as well as in Southeast Asian countries needs to be confirmed and revised using more comprehensive analyses based on morphology and other molecular techniques.

Echinostoma ` revolutum ¿ (Digenea: Echinostomatidae) species complex revisited: species delimitation based on novel molecular and morphological data gathered in Europe

“…Whereas the identifications based on comparisons with original species descriptions may be correct, failure to follow the subsequent taxonomic/systematic changes may results in 'discoveries' such as "Interestingly, this study revealed that E. revolutum was more closely aligned with E. recurvatum than the other species of genus Echinostoma (e.g., E. malayanum), contradicting traditional morphological taxonomy." (Saijuntha et al [63]) and "Interestingly, this study revealed that two species of genus Echinostoma, i.e. E. revolutum and E. malayanum do not cluster as a monophyletic clade and/or sister taxa."…”

“…Several notes of caution are required before considering the recent papers on "Echinostoma" spp. reported recently from Asian locations (Saijuntha et al [62][63][64]; Noikong et al [65]). First, the authors should be aware that annotations in GenBank solely reflect the identification (in most cases not supported by voucher material and/or morphological data) of the authors submitting the sequences.…”

“…Fourthly, the original papers should be consulted in order that the correct origin of the material sequenced is identified. For example, Saijuntha et al [63] assumed that the sequence U58102 of Morgan & Blair [25] was of an "Australian isolate". The provenance of this isolate is not annotated in GenBank but is clearly identified (i.e.…”

Phylogenetic relationships of some species of the family Echinostomatidae Odner, 1910 (Trematoda), inferred from nuclear rDNA sequences and karyological analysis

“…The use of molecular approaches to determine phylogenetic relationships of digeneans has grown very rapidly since 1990s and molecular-based studies on echinostomes have been carried out to date (Morgan and Blair 1995, 1998a, 1998b, 2000, Petrie et al 1996, Grabda-Kazubska et al 1998, Kostadinova et al 2003, Saijuntha et al 2011, Georgieva et al 2013, 2014, Noikong et al 2014, Selbach et al 2014, Kudlai et al 2015). The genus Echinochasmus Dietz, 1909 (as well as Echinostoma and Echinopharyphium ) is one of the most species–rich genera in Echinostomatidae (Kostadinova and Gibson 2000); however, no one species of this genus was involved in molecular phylogenetic studies of the Digenea (Cribb et al 2001, Olson et al 2003, Olson and Tkach 2005).…”

Low Genetic Diversity in Wide-Spread Eurasian Liver Fluke Opisthorchis felineus Suggests Special Demographic History of This Trematode Species

“…[42,43]. As a result, distinct species were molecularly identified, and genetic diversity within species has been estimated.…”