Mitochondrial Genome of the Eyeworm, Thelazia callipaeda (Nematoda: Spirurida), as the First Representative from the Family Thelaziidae

Abstract

Human thelaziosis is an underestimated parasitic disease caused by Thelazia species (Spirurida: Thelaziidae). The oriental eyeworm, Thelazia callipaeda, infects a range of mammalian definitive hosts, including canids, felids and humans. Although this zoonotic parasite is of socio-economic significance in Asian countries, its genetics, epidemiology and biology are poorly understood. Mitochondrial (mt) DNA is known to provide useful genetic markers to underpin fundamental investigations, but no mt genome had been characterized for any members of the family Thelaziidae. In the present study, we sequenced and characterized the mt genome of T. callipaeda. This AT-rich (74.6%) mt genome (13,668 bp) is circular and contains 12 protein-coding genes, 22 transfer RNA genes and two ribosomal RNA genes, but lacks an atp8 gene. All protein-coding genes are transcribed in the same direction; the gene order is the same as those of Dirofilaria immitis and Setaria digitata (Onchocercidae), but distinct from Dracunculus medinensis (Dracunculidae) and Heliconema longissimum (Physalopteridae). Phylogenetic analyses of the concatenated amino acid sequence data for all 12 protein-coding genes by Bayesian inference (BI) showed that T. callipaeda (Thelaziidae) is related to the family Onchocercidae. This is the first mt genome of any member of the family Thelaziidae and should represent a new source of genetic markers for studying the epidemiology, ecology, population genetics and systematics of this parasite of humans and other mammals.

Characterization of the complete mitochondrial genome of Spirocerca lupi: sequence, gene organization and phylogenetic implications

“…The open-reading frames were analysed with Open Reading Frame Finder (http://www.ncbi.nlm.nih.gov/gorf/gorf.html) using the invertebrate mitochondrial code, and subsequently compared with that of T . callipaeda [21]. Protein-coding gene sequences were translated into amino acid sequences using the invertebrate mitochondrial genetic code; amino acid sequences were aligned using default settings with MEGA 5.0 [26].…”

“…Protein-coding gene sequences were translated into amino acid sequences using the invertebrate mitochondrial genetic code; amino acid sequences were aligned using default settings with MEGA 5.0 [26]. Translation initiation and termination codons were identified by comparison with those of the spirurid nematodes reported previously [21,27]. For analyzing ribosomal RNA genes, putative secondary structures of 22 tRNA genes were identified using tRNAscan-SE [28], of the 22 tRNA genes, 14 were identified using tRNAscan-SE, the other 8 tRNA genes were found by eye inspection, and rRNA genes were identified by comparison with that of spirurid nematodes [21,27].…”

“…To date, although mt genome sequences have been sequenced for 12 species within the order Spirurida, only one mt genome (for Thelazia callipaeda ) is available within the family Thelaziidae [21]. Therefore, the objectives of the present study were to determine the complete mt genome sequence of S .…”

The complete mitochondrial genome of Toxascaris leonina: Comparison with other closely related species and phylogenetic implications

“…Selected for comparison were concatenated amino acid sequences predicted from published mt genomes of key ascaridoid nematodes representing the Ascaridomorpha, including the superfamily Ascaridoidea [Ascaris suum , Anisakis simplex (Kim et al, 2006), Baylisascaris ailuri, Baylisascaris schroederi, Baylisascaris transfuga (Xie et al, 2011a) Baylisascaris procyonis (Xie et al, 2011b), Contracaecum rudolphii B , T. canis, T. cati, Toxocara malaysiensis (Li et al, 2008b)], and the superfamily Heterakoidea [Ascaridia galli, Ascaridia columbae and Ascaridia sp. (Liu et al, 2013b)], and the superfamily Seuratoidea [Cucullanus robustus (Park et al, 2011)], using Thelazia callipaeda (GenBank accession number JX069968) as an outgroup (Liu et al, 2013c). All amino acid sequences (considering all homologous characters) were aligned using MUSCLE (Edgar, 2004), and ambiguously aligned regions were excluded using Gblocks online server (http://molevol.cmima.csic.es/castresana/Gblocks_server.html) with the default parameters (Talavera and Castresana, 2007) using the options for a less stringent selection, and then subjected to phylogenetic analysis using Bayesian inference (BI).…”

Morphological and Mitochondrial Genomic Characterization of Eyeworms (Thelazia callipaeda) from Clinical Cases in Central China

“…For spirurid nematodes, the mt genomes have been applied particularly to studies regarding phylogeny and evolution (Park et al, 2011; Liu et al, 2013a, 2015; Yilmaz et al, 2016). To date, there are 24 mitogenomes of the order Spirurida in GenBank representing eight families.…”