The complete mitochondrial genome of Oxyuris equi: Comparison with other closely related species and phylogenetic implications

The complete mitochondrial genome of Wellcomia compar (Spirurina: Oxyuridae) and its genome characterization and phylogenetic analysis

Wellcomia compar (Spirurina: Oxyuridae) is a pinworm that infects wild and captive porcupines. Despite clear records of its morphological structure, its genetics, systematics, and biology are poorly understood. This study aimed to determine the complete mitochondrial (mt) genome of W. compar and reconstruct its phylogenetic relationship with other nematodes. We sequenced the complete mt genome of W. comparand conducted phylogenetic analyses using concatenated coding sequences of 12 protein-coding genes (PCGs) by maximum likelihood and Bayesian inference. The complete mt genome is 14,373 bp in size and comprises 36 genes, including 12 protein-coding, two rRNA and 22 tRNA genes. Apart from 28 intergenic regions, one non-coding region and one overlapping region also occur. A comparison of the gene arrangements of Oxyuridomorpha revealed relatively similar features in W. compar and Wellcomia siamensis. Phylogenetic analysis also showed that W. compar and W. siamensis formed a sister group. In Oxyuridomorpha the genetic distance between W. compar and W. siamensis was 0.0805. This study reports, for the first time, the complete W. compar mt genome sequence obtained from Chinese porcupines. It provides genetic markers for investigating the taxonomy, population genetics, and phylogenetics of pinworms from different hosts and has implications for the diagnosis, prevention, and control of parasitic diseases in porcupines and other animals.

Anthelmintic resistance and novel control options in equine gastrointestinal nematodes

Control of equine nematodes has relied on benzimidazoles (BZs), tetrahydropyrimidines and macrocyclic lactones. The intensive use of anthelmintics has led to the development of anthelmintic resistance (AR) in equine cyathostomins and Parascaris equorum. Field studies indicate that BZ and pyrantel resistance is widespread in cyathostomins and there are also increasing reports of resistance to macrocyclic lactones in cyathostomins and P. equorum. The unavailability of reliable laboratory-based techniques for detecting resistance further augments the problem of nematode control in horses. The only reliable test used in horses is the fecal egg count reduction test; therefore, more focus should be given to develop and validate improved methodologies for diagnosing AR at an early stage, as well as determining the mechanisms involved in resistance development. Therefore, equine industry and researchers should devise and implement new strategies for equine worm control, such as the use of bioactive pastures or novel feed additives, and control should increasingly incorporate alternative and evidence-based parasite control strategies to limit the development of AR. This review describes the history and prevalence of AR in equine nematodes, along with recent advances in developing resistance diagnostic tests and worm control strategies in horses, as well as giving some perspective on recent research into novel control strategies.

The mitochondrial genome of Dipetalonema gracile from a squirrel monkey in China

Dipetalonema gracile is a common parasite in squirrel monkeys (Saimiri sciureus), which can cause malnutrition and progressive wasting of the host, and lead to death in the case of massive infection. This study aimed to identify a suspected D. gracile worm from a dead squirrel monkey by means of molecular biology, and to amplify its complete mitochondrial genome by polymerase chain reaction (PCR) and sequence analysis. The results identified the worm as D. gracile, and the full length of its complete mitochondrial genome was 13,584 bp, which contained 22 tRNA genes, 12 protein-coding genes, two rRNA genes, one AT-rich region and one small non-coding region. The nucleotide composition included A (16.89%), G (20.19%), T (56.22%) and C (6.70%), among which A + T = 73.11%. The 12 protein-coding genes used TTG and ATT as start codons, and TAG and TAA as stop codons. Among the 22 tRNA genes, only trnS1AGN and trnS2UCN exhibited the TΨC-loop structure, while the other 20 tRNAs showed the TV-loop structure. The rrnL (986 bp) and rrnS (685 bp) genes were single-stranded and conserved in secondary structure. This study has enriched the mitochondrial gene database of Dipetalonema and laid a scientific basis for further study on classification, and genetic and evolutionary relationships of Dipetalonema nematodes.

Comparative analyses of the complete mitochondrial genomes of Cyathostomum pateratum and Cyathostomum catinatum provide new molecular data for the evolution of Cyathostominae nematodes

The parasite Cyathostomum pateratum, which occurs in the large intestine of equines, is a common species of the subfamily Cyathostominae. Cyathostominae nematodes are a complex nematode group for which only limited genetic information has been reported. To re-examine the phylogenetic relationships among Cyathostominae nematodes, we sequenced the complete mitochondrial (mt) genome of Cy. pateratum and compared it with the mt genome of the congeneric species Cyathostomum catinatum. The complete mtDNA sequence of Cy. pateratum was 13,822 bp in length, 16 bp shorter than that of Cy. catinatum. The mtDNA sequences of both species contained 12 protein-coding genes, two rRNA genes and 22 tRNA genes, and all 36 genes were transcribed in the same direction and in the same strand. Pairwise comparisons of the 12 predicted amino acid sequences between Cy. catinatum and Cy. pateratum revealed differences of 0.4-3.1%; the least conserved sequence was that of cytochrome c oxidase subunit 3 (cox3). Phylogenetic analysis of the concatenated amino acid sequences using Bayesian inference and maximum likelihood methods showed that Cy. catinatum and Cy. pateratum clustered together with very high nodal support, and Cylicostephanus goldi was closer to the Cyathostomum nematodes than to other Cyathostominae nematodes. The mtDNA sequence of Cy. pateratum is reported here for the first time. The study will shed some light on the genetic evolution among parasitic nematodes in Cyathostomum.

According to mitochondrial DNA evidence, Parascaris equorum and Parascaris univalens may represent the same species

Parascarosis is caused mainly by parasitic infections with Parascaris equorum and Parascaris univalens, the most common ascarid nematodes, in the small intestine of equines. Parascarosis often causes severe illness and even death in foals and yearlings. In this study, we obtained the complete sequence of the P. equorum mitochondrial (mt) genome and compared its organization and structure with that of P. equorum Japan isolate (nearly complete), and the complete mtDNA sequences of P. univalens Switzerland and USA isolates. The complete mtDNA genome of P. equorum China isolate is 13,899 base pairs (bp), making it the smallest of the four genomes. All four Parascaris mt genomes are circular, and all genes are transcribed in the same direction. The P. equorum mtDNA genome consists of 12 protein-coding genes, two ribosomal RNA genes, 22 transfer (t) RNA genes and one non-coding region, which is consistent with P. equorum Japan isolate and P. univalens Switzerland isolate but distinct from P. univalens USA isolate, which has 20 tRNA genes. Differences in nucleotide sequences of the four entire mt genomes range from 0.1–0.9%, and differences in total amino acid sequences of protein-coding genes are 0.2–2.1%. Phylogenetic analyses showed that the four Parascaris species clustered in a clade, indicating that P. equorum and P. univalens are very closely related. These mt genome datasets provide genetic evidence that P. equorum and P. univalens may represent the same species, which will be of use in further studies of the taxonomy, systematics and population genetics of ascarids and other nematodes.

Mitochondrial DNA Evidence Supports the Hypothesis that Triodontophorus Species Belong to Cyathostominae

Equine strongyles, the significant nematode pathogens of horses, are characterized by high quantities and species abundance, but classification of this group of parasitic nematodes is debated. Mitochondrial (mt) genome DNA data are often used to address classification controversies. Thus, the objectives of this study were to determine the complete mt genomes of three Cyathostominae nematode species (Cyathostomum catinatum, Cylicostephanus minutus, and Poteriostomum imparidentatum) of horses and reconstruct the phylogenetic relationship of Strongylidae with other nematodes in Strongyloidea to test the hypothesis that Triodontophorus spp. belong to Cyathostominae using the mt genomes. The mt genomes of Cy. catinatum, Cs. minutus, and P. imparidentatum were 13,838, 13,826, and 13,817 bp in length, respectively. Complete mt nucleotide sequence comparison of all Strongylidae nematodes revealed that sequence identity ranged from 77.8 to 91.6%. The mt genome sequences of Triodontophorus species had relatively high identity with Cyathostominae nematodes, rather than Strongylus species of the same subfamily (Strongylinae). Comparative analyses of mt genome organization for Strongyloidea nematodes sequenced to date revealed that members of this superfamily possess identical gene arrangements. Phylogenetic analyses using mtDNA data indicated that the Triodontophorus species clustered with Cyathostominae species instead of Strongylus species. The present study first determined the complete mt genome sequences of Cy. catinatum, Cs. minutus, and P. imparidentatum, which will provide novel genetic markers for further studies of Strongylidae taxonomy, population genetics, and systematics. Importantly, sequence comparison and phylogenetic analyses based on mtDNA sequences supported the hypothesis that Triodontophorus belongs to Cyathostominae.

The mitochondrial genome of Ancylostoma tubaeforme from cats in China

Ancylostoma tubaeforme may infect canids, felids and humans, and pose a potential risk to public health. Polymerase chain reaction (PCR) techniques were used to amplify the complete mitochondrial (mt) genome sequence of A. tubaeforme from cats and to analyse its sequence characteristics after molecular identification based on the internal transcribed spacer ITS1+ sequence. The results show that the complete mt genome sequence (GenBank accession number KY070315) of A. tubaeforme from cats was 13,730 bp in length, including 12 protein-coding genes, 22 transfer RNA (tRNA) genes, two ribosomal RNA (rRNA) genes, two non-coding regions and an AT-rich region. The nucleotide content of A and T was 77.93%, biased toward A and T. Twelve protein-coding genes used ATT, TTG and GTG as initiation codons, and TAA, TAG, TA and T as termination codons. The length of the 22 tRNA genes ranged from 52 to 62 bp, their predicted secondary structures were D loops and V loops. The lengths of the two rRNAs were 958 and 697 bp. Phylogenetic analyses showed that A. tubaeforme from cats was in the lineage of Ancylostoma, having a close phylogenetic relationship with A. caninum. This study reports for the first time the mt genome of A. tubaeforme from cats in China, which could enhance the mt genome database of Ancylostomatidae nematodes, and it offers the scientific basis for further studies in the genetic diversity of hookworms among different hosts.

Comparative analyses of the complete mitochondrial genomes of the two murine pinworms Aspiculuris tetraptera and Syphacia obvelata

Pinworms Aspiculuris tetraptera and Syphacia obvelata are important parasitic nematodes of laboratory mice, rat and other rodents. However, the mitochondrial (mt) genome of these parasites have not been known yet. In the present study, the complete mt genomes of A. tetraptera and S. obvelata were sequenced, which were 13,669 bp and 14,235 bp in size, respectively. Both genomes included 12 protein-coding genes, two rRNA genes, 22 tRNA genes and one non-coding region. The mt genomes of A. tetraptera and S. obvelata preferred bases A and T, with the highest for T and the lowest for C. The mt gene arrangements of the two pinworms were the same as that of the GA8 type. Phylogenetic analysis using mtDNA data revealed that the Bayesian inference (BI) trees contained two big branches: species from Oxyuridomorpha, Rhabditomorpha and Ascaridomorpha formed one branch, and those from Spiruromorpha formed another branch with high statistical support. The two murine pinworms A. tetraptera and S. obvelata have closer relationship than to other pinworms. This study provides a foundation for studying the population genetics, systematics and molecular phylogeny of pinworms.