Contracaecum rudolphii B: Gene content, arrangement and composition of its complete mitochondrial genome compared with Anisakis simplex s.l

A multiple lateral flow immunoassay based on AuNP for the detection of 5 chemical contaminants in milk

Melamine (MEL), enrofloxacin (ENR), sulfamethazine (SMZ), tetracycline (TC), and aflatoxin M₁ (AFM₁) are the main chemical contaminants in milk. It is necessary to detect these miscellaneous chemical contaminants in milk synchronously to ensure the safety of the milk. In this study, a multiple lateral flow immunoassay (LFIA) was developed for the detection of MEL, ENR, SMZ, TC, and AFM₁ in milk. Under optimal experimental conditions, the cutoff values were 25 ng/mL for MEL, 1 ng/mL for ENR, 2.5 ng/mL for SMZ, 2.5 ng/mL for TC, and 0.25 ng/mL for AFM₁ in milk samples. The limits of detection of LFIA were 0.173 ng/mL for MEL, 0.078 ng/mL for ENR, 0.059 ng/mL for SMZ, 0.082 ng/mL for TC, and 0.0064 ng/mL for AFM₁. The recovery rates of LFIA in milk were 83.2-104.4% for MEL, 76.5-127.3% for ENR, 96.8-113.5% for SMZ, 107.1-166.6% for TC, and 93.5-130.3% for AFM₁. The coefficients of variation were all less than 15%. As a whole, the developed multiple lateral flow immunoassay showed potential as a highly reliable and excellent tool for the rapid and sensitive screening of MEL, ENR, SMZ, TC, and AFM₁ in milk.

The Complete Mitogenome of Toxocara vitulorum: Novel In-Sights into the Phylogenetics in Toxocaridae

Toxocara vitulorum (Ascaridida: Nematoda) is one of the most common intestinal nematodes of cattle and buffalos and, therefore, represents a serious threat to their populations worldwide. Despite its significance in veterinary health the epidemiology, population genetics, and molecular ecology of this nematode remain poorly understood. The mitogenome can yield a foundation for studying these areas and assist in the surveillance and control of T. vitulorum. Herein, the first whole mitogenome of T. vitulorum was sequenced utilizing Illumina technology and characterized with bioinformatic pipeline analyses. The entire genome of T. vitulorum was 15,045 bp in length and contained 12 protein-coding genes (PCGs), 22 transfer RNAs (tRNAs), and two ribosomal RNAs (rRNAs). The gene arrangement (GA) of T. vitulorum was similar to those of other Toxocara species under GA3. The whole genome showed significant levels of AT and GC skew. Comparative mitogenomics including sequence identities, Ka/Ks, and sliding window analysis, indicated a purifying selection of 12 PCGs with cox1 and nad6 having the lowest and highest evolutionary rate, respectively. Whole amino acid sequence-based phylogenetic analysis supported a novel sister-species relationship of T. vitulorum with the congeneric species Toxocara canis, Toxocara cati, and Toxocara malaysiensis in the family Toxocaridae. Further, 12 (PCGs) single gene-based phylogenies suggested that nad4 and nad6 genes shared same topological trees with that of the whole genome, suggesting that these genes were suitable as novel genetic markers for phylogenetic and evolutionary studies of Ascaridida species. This complete mitogenome of T. vitulorum refined phylogenetic relationships in Toxocaridae and provided the resource of markers for population genetics, systematics, and epidemiology of this bovine nematode.

New insights into the coexistence of Contracaecum rudolphii A and Contracaecum rudolphii B (Nematoda: Anisakidae) in Phalacrocorax carbo sinensis from Sardinia: genetic variability and phylogenetic analysis

Contracaecum sp. nematodes are important parasites of fish eating birds that can cause animal health problems. In the present study, specimens of Contracaecum rudolphii sensu lato, from the great cormorant Phalacrocorax carbo sinensis from Sardinia, were characterized based on morphological and molecular data. The morphological analysis allowed to identify all the fourth stage larvae (n = 1918) as Contracaecum sp., and adults, male (n = 5845) and female (n = 8312), as C. rudolphii sensu lato. Population genetics and phylogenetic relationships were inferred based on mitochondrial and nuclear markers. Multiple sequence alignment of the ribosomal internal transcribed spacer showed the coexistence of C. rudolphii A (n = 157), C. rudolphii B (n = 22) and a rare heterozygote of these species. Moreover, mitochondrial markers, namely NADH dehydrogenase subunits I (nad1), cytochrome c oxidase subunit (cox1 and cox2) and small subunit of rRNA (rrnS), showed that the studied C. rudolphii A populations had undergone bottleneck, or founder effect event, subsequent to a rapid population growth and expansion. The observed heterozygote is with a mitochondrial pattern of C. rudolphii B. Although, both Contracaecum species showed high genetic diversity, no genetic structure between localities was detected. Phylogenetic reconstructions supported the paraphyly of the avian Contracaecum species including C. ogmorhini (parasite of otariids).

Identification and genetic characterization of Contracaecum sp. (Nematoda Anisakidae) from China

Contracaecum species are economically important fish-borne larval nematodes with zoonotic significance. In June 2019, more than one hundred piscivorous birds were died in its habitats close to the Wild Duck Lake, located in Yanqing, northwest of Beijing, China. Post-mortem examination of Black Night Herons (Nycticorax) revealed the presence of numerous anisakid nematodes in the proventriculus. Recovered nematodes were identified as Contracaecum sp. based on morphological description. Phylogenetic analysis of the mitochondrial (mt) genome and the ITS gene showed that sequences of Contracaecum sp. Beijing isolates were grouped into a new individual cluster. Furthermore, the parasite was successfully isolated from fresh dead birds, feces of piscivorous birds, and fish and prevalence ranged from 8.0% to 81.8%. Consequently, our study demonstrated the Contracaecum sp. infections in different sources from China, which might constitute a threat to wildlife, aquaculture, and public health. This article is protected by copyright. All rights reserved.

Morphological and Molecular Characteristics of the Gastro-Intestinal Nematode Parasite Ascaridia columbae Infecting the Domestic Pigeon Columba livia domestica in Saudi Arabia

BACKGROUND

Parasitism is a complex problem that is often ignored in companion animals, including birds, unless it develops into a severe clinical disorder. The present study was, therefore, aimed to investigate the presence of the gastrointestinal nematode infecting the domestic pigeon and provide a complete morphological description and clarify its taxonomic position through phylogenetic analysis of the ITS1-5.8s-ITS2 rDNA gene region.

MATERIALS AND METHODS

During the current study, a total of twenty-six domestic pigeons, Columba livia domestica, were collected and internal organs examined for helminth detection. Using light and scanning electron microscopy, the recovered parasite species are studied. In addition, the selected gene region was obtained and sequenced using appropriate primers that aid in the formation of the phylogenetic dendrogram for the recovered parasite species with others retrieved from GenBank.

RESULTS

Morphological examination showed that this nematode parasite belongs to the Ascaridiidae family within the genus Ascaridia. The material was assigned to the previously described Ascaridia columbae by providing all the characteristic features as the presence of a mouth opening surrounded by three tri-lobed lips; each lip has two triangular teeth with a spoon-like structure, cephalic papillae and amphidal pores on lips surface, presence of lateral cuticular alae and pre-cloacal sucker, 10 pairs of caudal papillae, and two equal spicules in male worms. The morphological investigations of this species were supplemented by molecular analysis of ITS1-5.8s-ITS2 rDNA gene region. The data showed that the present A. coulmbae is deeply embedded in the Ascaridia genus with a 74-99% sequence similarity to other species in the Chromadorea class. Ascaridiidae appears as monophyly and represented as a sister group to Heterakidae. The ascaridiid species examined belong to the Ascaridia genus and displaced a close relationship with the previously described A. coulmbae (gb| KF147909.1, gb| AJ001509.1, gb| KC905082.1, gb| JQ995321.1, gb| JX624729.1) as putative sister taxa.

CONCLUSION

The present study revealed that the species Ascaridia is the first account of this genus as an endoparasite from the domestic pigeon inhabiting Saudi Arabia. Therefore, the combination of morphological and molecular studies helps to identify this species correctly and identified as Ascaridia columbae.

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.

Characterization of the complete mitochondrial genome of Ortleppascaris sinensis (Nematoda: Heterocheilidae) and comparative mitogenomic analysis of eighteen Ascaridida nematodes

Ortleppascaris sinensis (Nematoda: Ascaridida) is a dominant intestinal nematode of the captive Chinese alligator. However, the epidemiology, molecular ecology and population genetics of this parasite remain largely unexplored. In this study, the complete mitochondrial (mt) genome sequence of O. sinensis was first determined using a polymerase chain reaction (PCR)-based primer-walking strategy, and this is also the first sequencing of the complete mitochondrial genome of a member of the genus Ortleppascaris. The circular mitochondrial genome (13,828 bp) of O. sinensis contained 12 protein-coding, 22 transfer RNA and 2 ribosomal RNA genes, but lacked the ATP synthetase subunit 8 gene. Finally, phylogenetic analysis of mtDNAs indicated that the genus Ortleppascaris should be attributed to the family Heterocheilidae. It is necessary to sequence more mtNDAs of Ortleppascaris nematodes in the future to test and confirm our conclusion. The complete mitochondrial genome sequence of O. sinensis reported here should contribute to molecular diagnosis, epidemiological investigations and ecological studies of O. sinensis and other related Ascaridida nematodes.

Mitochondrial Phylogenomics yields Strongly Supported Hypotheses for Ascaridomorph Nematodes

Ascaridomorph nematodes threaten the health of humans and other animals worldwide. Despite their medical, veterinary and economic importance, the identification of species lineages and establishing their phylogenetic relationships have proved difficult in some cases. Many working hypotheses regarding the phylogeny of ascaridomorphs have been based on single-locus data, most typically nuclear ribosomal RNA. Such single-locus hypotheses lack independent corroboration, and for nuclear rRNA typically lack resolution for deep relationships. As an alternative approach, we analyzed the mitochondrial (mt) genomes of anisakids (~14 kb) from different fish hosts in multiple countries, in combination with those of other ascaridomorphs available in the GenBank database. The circular mt genomes range from 13,948-14,019 bp in size and encode 12 protein-coding genes, 2 ribosomal RNAs and 22 transfer RNA genes. Our analysis showed that the Pseudoterranova decipiens complex consists of at least six cryptic species. In contrast, the hypothesis that Contracaecum ogmorhini represents a complex of cryptic species is not supported by mt genome data. Our analysis recovered several fundamental and uncontroversial ascaridomorph clades, including the monophyly of superfamilies and families, except for Ascaridiidae, which was consistent with the results based on nuclear rRNA analysis. In conclusion, mt genome analysis provided new insights into the phylogeny and taxonomy of ascaridomorph nematodes.

Mitochondrial genomes of Heterakis gallinae and Heterakis beramporia support that they belong to the infraorder Ascaridomorpha

Heterakis gallinae and Heterakis beramporia are the most prevalent nematode infecting native chicken breed, causing major economic losses. In the present study, the complete mitochondrial genomes (mt) of H. gallinae and H. beramporia were amplified by long-PCR and then sequenced. The complete mt genomes of H. gallinae and H. beramporia were 13,973bp and 14,012bp in size, respectively. Both mt genomes contain 12 protein-coding genes, 22 transfer RNA genes and 2 ribosomal RNA genes. All genes are transcribed in the same direction and the gene arrangement is identical to Ascaridia spp. Phylogenetic analysis based on the 12 protein-coding genes revealed that the family Heterakidae (represented by H. gallinae and H. beramporia) was more closely related to the infraorder Ascaridomorpha than it was to the infraorder Oxyuridomorpha. The present study determined the complete mt genome sequences for two Heterakis species, providing useful markers for studying the systematics, population genetics, and molecular epidemiology of these Heterakis parasites.

The complete mitochondrial genome of rabbit pinworm Passalurus ambiguus: genome characterization and phylogenetic analysis

Passalurus ambiguus (Nematda: Oxyuridae) is a common pinworm which parasitizes in the caecum and colon of rabbits. Despite its significance as a pathogen, the epidemiology, genetics, systematics, and biology of this pinworm remain poorly understood. In the present study, we sequenced the complete mitochondrial (mt) genome of P. ambiguus. The circular mt genome is 14,023 bp in size and encodes of 36 genes, including 12 protein-coding, two ribosomal RNA, and 22 transfer RNA genes. The mt gene order of P. ambiguus is the same as that of Wellcomia siamensis, but distinct from that of Enterobius vermicularis. Phylogenetic analyses based on concatenated amino acid sequences of 12 protein-coding genes by Bayesian inference (BI) showed that P. ambiguus was more closely related to W. siamensis than to E. vermicularis. This mt genome provides novel genetic markers for studying the molecular epidemiology, population genetics, systematics of pinworm of animals and humans, and should have implications for the diagnosis, prevention, and control of passaluriasis in rabbits and other animals.

The complete mitochondrial genome of Pseudoterranova azarasi and comparative analysis with other anisakid nematodes

Anisakiasis/anisakidosis caused by anisakid nematodes is an emerging infectious disease that can cause a wide range of clinical syndromes and are difficult to diagnose and treat in humans. In spite of their significance as pathogens, the systematics, genetics, epidemiology and biology of these parasites remain poorly understood. In the present study, we sequenced the complete mitochondrial (mt) genome of Pseudoterranova azarasi, which is one of the most important zoonotic anisakid parasites. The circular mt genome is 13,954 bp in size and encodes of 36 genes, including 12 protein-coding, 2 ribosomal RNA and 22 transfer RNA genes. The mt gene order of P. azarasi is the same as those of Ascaris spp. (Ascarididae), Toxocara spp. (Toxocaridae) and Anisakis simplex (Anisakidae), but distinct from those of Ascaridia spp. (Ascaridiidae) and Cucullanus robustus (Cucullanidae). Phylogenetic analyses based on concatenated amino acid sequences of 12 protein-coding genes by Bayesian inference (BI) showed that Pseudoterranova were more closely related to Anisakis than they were to Contracaecum with strong a posterior probability support. This mt genome provides a novel genetic markers for exploring cryptic/sibling species and host affiliations, and should have implications for the diagnosis, prevention and control of anisakidosis in humans.

Coevolution between Contracaecum (Nematoda, Anisakidae) and Austrolebias (Cyprinodontiformes, Rivulidae) host-parasite complex from SW Atlantic coastal basins

In recent years, molecular studies in host-parasite interactions in terms of coevolution have become important. Larvae (L3) of two species of Contracaecum were found parasitizing species of Rivulidae in the Atlantic coastal basins from Uruguay. The aim of this study is to determine the patterns of differentiation of this host-parasite complex in order to clarify possible coevolutionary events in such interaction throughout phylogeographic approach using both nuclear and mitochondrial molecular markers (internal transcribed spacers (ITS) and cytochrome oxidase subunit 1 (cox-1)). Based on both markers, intraspecific variation in Contracaecum species was lower than 2 %, while interspecific variation was greater than 10 %. Both species of Contracaecum constitute monophyletic groups. Contracaecum resulted in a paraphyletic genus when incorporating other Contracaecum species and closely related nematode sequences from GenBank. ITS regions showed that Contracaecum sp. 1 is more closely related to other species of the same genus than with their counterparts from Atlantic coastal basins in Uruguay. Haplotype network for both markers corroborate the existence of two distinct taxa. While ITS pairwise FST comparisons and the indirect estimate of gene flow confirm the existence of two distinct Contracaecum species, mitochondrial gene detected low levels of migrants between some of the populations from both species. Our results suggest that coevolution in this host-parasite complex species is plausible. Parasite cladogenetic events occur almost simultaneously with the separation of the hypothetical ancestors of each species complex of Austrolebias during Pliocene. Additionally, the two lineages of Contracaecum colonize differently the species within each of the Austrolebias complexes.

The mitochondrial genome of Parascaris univalens--implications for a "forgotten" parasite

Background

Parascaris univalens is an ascaridoid nematode of equids. Little is known about its epidemiology and population genetics in domestic and wild horse populations. PCR-based methods are suited to support studies in these areas, provided that reliable genetic markers are used. Recent studies have shown that mitochondrial (mt) genomic markers are applicable in such methods, but no such markers have been defined for P. univalens.

Methods

Mt genome regions were amplified from total genomic DNA isolated from P. univalens eggs by long-PCR and sequenced using Illumina technology. The mt genome was assembled and annotated using an established bioinformatic pipeline. Amino acid sequences inferred from all protein-encoding genes of the mt genomes were compared with those from other ascaridoid nematodes, and concatenated sequences were subjected to phylogenetic analysis by Bayesian inference.

Results

The circular mt genome was 13,920 bp in length and contained two ribosomal RNA, 12 protein-coding and 22 transfer RNA genes, consistent with those of other ascaridoids. Phylogenetic analysis of the concatenated amino acid sequence data for the 12 mt proteins showed that P. univalens was most closely related to Ascaris lumbricoides and A. suum, to the exclusion of other ascaridoids.

Conclusions

This mt genome representing P. univalens now provides a rich source of genetic markers for future studies of the genetics and epidemiology of this parasite and its congener, P. equorum. This focus is significant, given that there is no published information on the specific prevalence and distribution of P. univalens infection in domestic and wild horse populations.

Electronic supplementary material

The online version of this article (doi:10.1186/1756-3305-7-428) contains supplementary material, which is available to authorized users.

Comparative analyses of the complete mitochondrial genomes of the two ruminant hookworms Bunostomum trigonocephalum and Bunostomum phlebotomum

Bunostomum trigonocephalum and Bunostomum phlebotomum are blood-feeding hookworms of sheep and cattle, causing considerable economic losses to the live stock industries. Studying genetic variability within and among hookworm populations is critical to addressing epidemiological and ecological questions. Mitochondrial (mt) DNA is known to provide useful markers for investigations of population genetics of hookworms, but mt genome sequence data are scant. In the present study, the complete mitochondrial DNA (mtDNA) sequences of the sheep and goat hookworm B. trigonocephalum were determined for the first time, and the mt genome of B. phlebotomum from yak in China was also sequenced for comparative analyses of their gene contents and genome organizations. The lengths of mt DNA sequences of B. trigonocephalum sheep isolate, B. trigonocephalum goat isolate and B. phlebotomum China yak isolate were 13,764bp, 13,771bp and 13,803bp in size, respectively. The identity of the mt genomes was 99.7% between B. trigonocephalum sheep isolate and B. trigonocephalum goat isolate. The identity of B. phlebotomum China yak isolate mt genomes was 85.3% with B. trigonocephalum sheep isolate, and 85.2% with B. trigonocephalum goat isolate. All the mt genes of the two hookworms were transcribed in the same direction and gene arrangements were consistent with those of the GA3 type, including 12 protein-coding genes, 2 rRNA genes and 22 tRNA genes, but lacking ATP synthetase subunit 8 gene. The mt genomes of B. trigonocephalum and B. phlebotomum were similar to prefer bases A and T, the contents of A+T are 76.5% (sheep isolate), 76.4% (goat isolate) and 76.9% (China yak isolate), respectively. Phylogenetic relationships reconstructed using concatenated amino acid sequences of 12 protein-coding genes with three methods (maximum likelihood, Bayesian inference and neighbor joining) revealed that the B. trigonocephalum and B. phlebotomum represent distinct but closely-related species. These data provide novel and useful genetic markers for studying the systematics, and population genetics of the two ruminant hookworms.

Complete mitochondrial genomes of chimpanzee- and gibbon-derived Ascaris isolated from a zoological garden in southwest China

Roundworms (Ascaridida: Nematoda), one of the most common soil-transmitted helminths (STHs), can cause ascariasis in various hosts worldwide, ranging from wild to domestic animals and humans. Despite the veterinary and health importance of the Ascaridida species, little or no attention has been paid to roundworms infecting wild animals including non-human primates due to the current taxon sampling and survey bias in this order. Importantly, there has been considerable controversy over the years as to whether Ascaris species infecting non-human primates are the same as or distinct from Ascaris lumbricoides infecting humans. Herein, we first characterized the complete mitochondrial genomes of two representative Ascaris isolates derived from two non-human primates, namely, chimpanzees (Pan troglodytes) and gibbons (Hylobates hoolock), in a zoological garden of southwest China and compared them with those of A. lumbricoides and the congeneric Ascaris suum as well as other related species in the same order, and then used comparative mitogenomics, genome-wide nucleotide sequence identity analysis, and phylogeny to determine whether the parasites from chimpanzees and gibbons represent a single species and share genetic similarity with A. lumbricoides. Taken together, our results yielded strong statistical support for the hypothesis that the chimpanzee- and gibbon-derived Ascaris represent a single species that is genetically similar to A. lumbricoides, consistent with the results of previous morphological and molecular studies. Our finding should enhance public alertness to roundworms originating from chimpanzees and gibbons and the mtDNA data presented here also serves to enrich the resource of markers that can be used in molecular diagnostic, systematic, population genetic, and evolutionary biological studies of parasitic nematodes from either wild or domestic hosts.

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

Adults of Toxascaris leonina (Nematoda: Ascarididae) live in the gastrointestinal tract of both dogs and cats, and cause significant economic losses and potential public health problem worldwide. Although many studies have given insights into this significant pathogen, to date, the complete mitochondrial (mt) genome sequence is still not available for T. leonina. Here, we sequenced the complete mt genome of T. leonina. This AT-rich (71.53%) mt genome (14,310bp) is circular and consists of 36 genes, including 12 genes for proteins, 2 genes for rRNA and 22 genes for tRNA. All mt genes of T. leonina are transcribed in the same direction. The gene order is the same as those of Ascaris spp. (Ascarididae), Toxocara spp. (Toxocaridae), Anisakis simplex and Contracaecum rudolphii B (Anisakidae), but distinct from that of Ascaridia spp. (Ascaridiidae). Phylogenetic analyses using concatenated amino acid sequences of 12 protein-coding genes by Bayesian inference (BI) showed distinct groups with high statistical support, and our data confirm that T. leonina is a member of the Ascarididae, and that this family is more closely related to the Toxocaridae rather than the Anisakidae within the Ascaridoidea. The determination of mt genome sequences of T. leonina provides novel genetic markers for studies into the systematics, population genetics and epidemiology of this parasite.

Mitochondrial genomes of Anisakis simplex and Contracaecum osculatum (sensu stricto)--comparisons with selected nematodes

Anisakid nematodes parasitize mainly fish, marine mammals and/or fish-eating birds, and can be transmitted to a range of fish-eating mammals, including humans, where they can cause gastrointestinal disease linked to larval infection or allergic responses. In spite of the animal and human health significance of these parasites, there are still gaps in our understanding of the systematics, biology, epidemiology and ecology of anisakids. Mitochondrial (mt) DNA provides useful genetic markers for investigations in these areas, but complete mt genomic data have been lacking for most anisakids. In the present study, the mt genomes of Anisakis simplex sensu stricto and Contracaecum osculatum sensu stricto were amplified from genomic DNA by long-range polymerase chain reaction and sequenced using 454 technology. The circular mt genomes of these species were 13,926 and 13,823 bp, respectively, and each of them contained 12 protein-coding, 22 transfer RNA, and 2 ribosomal RNA genes consistent for members of the Ascaridida, Oxyurida, Spirurida, Rhabditida and Strongylida. These mt genomes provide a stepping-stone for future comparative analyses of a range of anisakids and a basis for reinvestigating their genetic relationships. In addition, these markers might be used in prospecting for cryptic species and exploring host affiliations.

The complete mitochondrial genomes of three parasitic nematodes of birds: a unique gene order and insights into nematode phylogeny

Background

Analyses of mitochondrial (mt) genome sequences in recent years challenge the current working hypothesis of Nematoda phylogeny proposed from morphology, ecology and nuclear small subunit rRNA gene sequences, and raise the need to sequence additional mt genomes for a broad range of nematode lineages.

Results

We sequenced the complete mt genomes of three Ascaridia species (family Ascaridiidae) that infest chickens, pigeons and parrots, respectively. These three Ascaridia species have an identical arrangement of mt genes to each other but differ substantially from other nematodes. Phylogenetic analyses of the mt genome sequences of the Ascaridia species, together with 62 other nematode species, support the monophylies of seven high-level taxa of the phylum Nematoda: 1) the subclass Dorylaimia; 2) the orders Rhabditida, Trichinellida and Mermithida; 3) the suborder Rhabditina; and 4) the infraorders Spiruromorpha and Oxyuridomorpha. Analyses of mt genome sequences, however, reject the monophylies of the suborders Spirurina and Tylenchina, and the infraorders Rhabditomorpha, Panagrolaimomorpha and Tylenchomorpha. Monophyly of the infraorder Ascaridomorpha varies depending on the methods of phylogenetic analysis. The Ascaridomorpha was more closely related to the infraorders Rhabditomorpha and Diplogasteromorpha (suborder Rhabditina) than they were to the other two infraorders of the Spirurina: Oxyuridorpha and Spiruromorpha. The closer relationship among Ascaridomorpha, Rhabditomorpha and Diplogasteromorpha was also supported by a shared common pattern of mitochondrial gene arrangement.

Conclusions

Analyses of mitochondrial genome sequences and gene arrangement has provided novel insights into the phylogenetic relationships among several major lineages of nematodes. Many lineages of nematodes, however, are underrepresented or not represented in these analyses. Expanding taxon sampling is necessary for future phylogenetic studies of nematodes with mt genome sequences.

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

Background

Spirocerca lupi is a life-threating parasitic nematode of dogs that has a cosmopolitan distribution but is most prevalent in tropical and subtropical countries. Despite its veterinary importance in canids, the epidemiology, molecular ecology and population genetics of this parasite still remain unexplored.

Methods

The complete mitochondrial (mt) genome of S. lupi was amplified in four overlapping long fragments using primers designed based on partial cox1, rrnS, cox2 and nad2 sequences. Phylogenetic re-construction of 13 spirurid species (including S. lupi) was carried out using Bayesian inference (BI) based on concatenated amino acid sequence datasets.

Results

The complete mt genome sequence of S. lupi is 13,780 bp in length, including 12 protein-coding genes, 22 transfer RNA genes and two ribosomal RNA genes, but lacks the atp8 gene. The gene arrangement is identical to that of Thelazia callipaeda (Thelaziidae) and Setaria digitata (Onchocercidae), but distinct from that of Dracunculus medinensis (Dracunculidae) and Heliconema longissimum (Physalopteridae). All genes are transcribed in the same direction and have a nucleotide composition high in A and T. The content of A + T is 73.73% for S. lupi, in accordance with mt genomes of other spirurid nematodes sequenced to date. Phylogenetic analyses using concatenated amino acid sequences of the 12 protein-coding genes by BI showed that the S. lupi (Thelaziidae) is closely related to the families Setariidae and Onchocercidae.

Conclusions

The present study determined the complete mt genome sequence of S. lupi. These new mt genome dataset should provide novel mtDNA markers for studying the molecular epidemiology and population genetics of this parasite, and should have implications for the molecular diagnosis, prevention and control of spirocercosis in dogs and other canids.

Further studies on Contracaecum spasskii Mozgovoi, 1950 and C. rudolphii Hartwich, 1964 (sensu lato) (Ascaridida: Anisakidae) from piscivorous birds in China

Contracaecum spasskii Mozgovoi, 1950, collected from the great crested grebe Podiceps cristatus (Linnaeus) (Podicipediformes: Podicipedidae), is redescribed using both light and, for the first time, scanning electron microscopy. Contracaecum spasskii differs from its congeners by having marked transverse cuticular annulations, the length of the oesophagus and spicules, the ratio between the intestinal caecum and the ventricular appendix, the number and arrangement of male caudal papillae, and especially by the particular morphology of the lips and interlabia. Some previously unreported morphological features of C. spasskii are also revealed and others corrected. Contracaecum rudolphii Hartwich, 1964 (sensu lato) is also redescribed based on the specimens collected from the great cormorant Phalacrocorax carbo sinensis (Blumenbach) (Pelecaniformes: Phalacrocoracidae) from China. Based on the geographical perspective, the present Chinese material may represent the species C. rudolphii B.

Oesophagostomum dentatum and Oesophagostomum quadrispinulatum: characterization of the complete mitochondrial genome sequences of the two pig nodule worms

In the present study, the complete mitochondrial DNA (mtDNA) sequences of the pig nodule worm Oesophagostomum quadrispinulatum were determined for the first time, and the mt genome of Oesophagostomum dentatum from China was also sequenced for comparative analysis of their gene contents and genome organizations. The mtDNA sequences of O. dentatum China isolate and O. quadrispinulatum were 13,752 and 13,681 bp in size, respectively. Each of the two mt genomes comprises 36 genes, including 12 protein-coding genes, two ribosomal RNA and 22 transfer RNA genes, but lacks the ATP synthetase subunit 8 gene. All genes are transcribed in the same direction and have a nucleotide composition high in A and T. The contents of A+T are 75.79% and 77.52% for the mt genomes of O. dentatum and O. quadrispinulatum, respectively. Phylogenetic analyses using concatenated amino acid sequences of the 12 protein-coding genes, with three different computational algorithms (maximum likelihood, maximum parsimony and Bayesian inference), all revealed that O. dentatum and O. quadrispinulatum represent distinct but closely-related species. These data provide novel and useful markers for studying the systematics, population genetics and molecular diagnosis of the two pig nodule worms.