Adults of Hysteromorpha triloba (Rudolpi, 1819), Lutz, 1931 inhabit primarily the intestine of cormorants across the globe, whereas metacercariae have been found in the body cavity of freshwater fishes of the families Cyprinidae, Ictaluridae, Ariidae, Pimelodidae and Catostomidae. In this study, adults and metacercariae identified as H. triloba were collected from the Neotropical cormorant (Nannopterum brasilianus) and from the Mexican tetra fish (Astyanax mexicanus) from the Gulf of Mexico and Pacific Ocean slopes in the Neotropical region. Partial DNA sequences of the mitochondrial gene cytochrome c oxidase subunit I (cox 1) and the internal transcribed spacers (ITS1, 5.8S and ITS2) of nuclear ribosomal DNA were generated for both developmental stages, and were compared with available sequences of H. triloba from the Nearctic region. The genetic divergence between metacercariae and adults of H. triloba from the Neotropical and Nearctic region (Canada) associated with the double-crested cormorant (Nannopterum auritus), ranged from 0 to 5.5% for cox 1 and from 0 to 0.2% for ITS. Phylogenetic analyses inferred with both molecular markers using maximum likelihood and Bayesian inference placed the adults and metacercariae in a single clade, confirming that both stages are conspecific. Our data confirmed that H. triloba is a widely distributed species across the Americas, parasitizing both the Neotropical and Nearctic cormorants in Argentina, Brazil, Venezuela, Mexico, USA and Canada.

Despite the advances of molecular tools, new nematode species are still described mainly based on morphological characters. Parapharyngodon and Thelandros are two genera of oxyurids with unclear related taxonomic histories. Here we use morphological characters (linear measurements and categorical variables) and genetic information (18S rRNA, 28S rRNA and COI partial gene sequences) to confirm the relationships between representatives of these two genera and to determine whether they can be discriminated morphologically. Genetic results confirm the existence of two main clades, mostly congruent with Parapharyngodon and Thelandros genera but with several discordances. Thelandros is polyphyletic, with two of the species analysed (T. filiformis and T. tinerfensis) being part of the Thelandros clade, but with a third one (T. galloti) falling within the Parapharyngodon clade. Regarding the Parapharyngodon clade, P. cubensis, P. scleratus and Parapharyngodon sp. from Mexico form congruent lineages, while most P. echinatus samples cluster in another group, with one exception. Interestingly, P. micipsae samples are scattered across the Parapharyngodon clade, suggesting that they were misidentified or rather represent alternative morphotypes of other species. Morphological analysis identified the length of the tail, number of caudal papillae, position of the nerve ring, presence of caudal alae and length of the lateral alae as reliable characters to distinguish between Parapharyngodon and Thelandros genetic clades. Our study highlights the current taxonomic inconsistency in these groups, mainly derived from the exclusive use of morphological data. As such, we advocate for the routine implementation of molecular data in nematode taxonomic studies.

In this study, molecular (ribosomal sequence data), morphological and cross-hybridization properties were used to identify a new Steinernema sp. from Florida, USA. Molecular and morphological data provided evidence for placing the novel species into Clade V, or the ‘glaseri-group’ of Steinernema spp. Within this clade, analysis of sequence data of the rDNA genes, 28S and internal transcribed spacer (ITS), depicted the novel species as a distinctive entity and closely related to S. glaseri and S. cubanum. Additionally, cross-hybridization assays showed that the new species is unable to interbreed with either of the latter two species, reinforcing its uniqueness from a biological species concept standpoint. Key morphological diagnostic characters for S. khuongi n. sp. include the mean morphometric features of the third-stage infective juveniles: total body length (average: 1066 μm), tail length (average: 65 μm), location of the excretory pore (average: 80.5 μm) and the values of c (average: 16.4), D% (average: 60.5), E% (average: 126) and H% (average: 46.6). Additionally, males can be differentiated from S. glaseri and S. cubanum by the values of several ratios: D% (average: 68), E% (average: 323) and SW% (average: 120). The natural distribution of this species in Florida encompasses both natural areas and citrus groves, primarily in shallow groundwater ecoregions designated as ‘flatwoods’. The morphological, molecular, phylogenetic and ecological data associated with this nematode support its identity as a new species in the S. glaseri-group.

The new species Metaxonchium toroense n. sp. from natural habitats of Costa Rica is described, including light microscopy (LM), scanning electron microscopy (SEM) and molecular (D2–D3 28S rDNA) analyses. The new species is characterized by its general size, the dimensions and appearance of its lip region, the length of the odontostyle and its fusiform aspect, the length of the neck and its pharyngeal expansion, the reduction of the anterior genital branch to a very short uterine sac without any rudiment of ovary or oviduct, tripartite and non-echinophor posterior uterus, the somewhat posterior vulva position, the length and shape of the caudal region, and the absence of males. Molecular analyses, the first to be performed on a Metaxonchium species, show a close relationship of the new species with representatives of the genera Axonchoides and Syncheilaxonchium.

The root-knot nematode species Meloidogyne daklakensis n. sp. was discovered on the roots of Robusta coffee (Coffea canephora Pierre ex A. Froehner) in Dak Lak Province, Vietnam. This species is characterized by the females having rounded or oval perineal patterns, smooth, regular, continuous striae, and reduced lateral lines. The dorsal arch is low, rounded and encloses a quite distinct vulva and tail tip. The stylet is normally straight with well-developed and posteriorly sloped knobs. The males have a rounded cap that extends posteriorly into the lip region. The procorpus is outlined distinctly, and is three times longer than the metacorpus. The metacorpus is ovoid, with a strong valve apparatus. The species closely resembles M. marylandi, M. naasi, M. ovalis, M. panyuensis, M. lopezi, M. mali and M. baetica in the perineal pattern of the females, and the morphology of the males and the second-stage juveniles. Nonetheless, it can be differentiated from other species by a combination of morphometric, morphological and molecular characteristics. Phylogenetic analysis was conducted based on the internal transcribed spacer (ITS) and 28S rDNA as well as the region between the cytochrome c oxidase I (COI) and cytochrome c oxidase II (COII) mitochondrial genes. Herein, this nematode is described, illustrated, and designated as a new species, Meloidogyne daklakensis sp. n., based on morphometric, morphological and molecular analyses.

Susceptibility and tolerance to parasite infection vary greatly between host species. The congeneric isopod species Austridotea annectens and Austridotea lacustris often occur in sympatry and can both serve as intermediate hosts for the trematode Maritrema poulini. However, the intensity and prevalence of infections vary greatly in natural populations, with A. annectens often being heavily infected and A. lacustris rarely being infected. To shed light on the factors that may be involved in infection avoidance in A. lacustris, 100 isopods were collected and experimentally exposed to M. poulini cercariae. To examine for potential behavioural mechanisms, we used carbonated water as a paralysing agent to temporarily stop any movement by the isopods, and exposed paralysed isopods to cercariae. In the experiments, none of the individuals that were exposed to the parasite were found to be infected, although some cercariae seemed to have penetrated isopod hosts. Behavioural defence mechanisms do not seem to explain the different infection levels between A. lacustris and A. annectens, suggesting a physiological, possibly immunological, factor may be present. At the ecosystem level, this suggests a potential dilution effect caused by this low-competency host, and its effects on parasite transmission dynamics should be investigated.

Diaphanocephalus galeatus collected from the small intestine of the lizard Dracaena paraguayensis in the Pantanal wetlands, State of Mato Grosso do Sul, Brazil, is redescribed. Genetic characterization and observations using scanning electron microscopy (SEM) were performed for the first time. The vouchers of D. galeatus and the type specimens of its congeners, deposited in the Coleção Helmintológica do Instituto Oswaldo Cruz (CHIOC), were consulted. Light and SEM observations revealed several undescribed features of D. galeatus, i.e. structure of the cephalic end and of the buccal capsule, position and morphology of deirids, presence of phasmids in females and presence of unpaired papilla on the membranous projection that covers the genital cone in males. After observation of the specimens deposited in the helminthological collection, D. jacuruxi is considered a synonym of D. galeatus, and D. diesingi, despite its incomplete description, is tentatively retained as valid due to the poor condition of the type material. The results also indicated low host specificity of D. galeatus, contradicting previous assertions. Genetic comparisons using patristic distances and phylogenetic trees generated from sequences of the 28S rRNA nuclear gene indicated that D. galeatus is closer to the taxa within Ancylostomatoidea and Strongyloidea than any lineage of Metastrongyloidea or Trichostrongyloidea. However, most of the nodal supports were low. Based on the genetic and morphological characterization, the validity of D. galeatus was confirmed. These data may serve for further comparative approaches for different populations of the parasite, from different hosts in different geographical areas, mitigating taxonomic confusions.

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.

Three species belonging to the genus Macrolaimus, namely M. canadensis, M. crucis and M. ruehmi, have been obtained from areas of natural vegetation in Bosnia and Herzegovina, Corsica (France), the Czech Republic and Spain. These three species are characterized by the body length of males and females, stomatal proportion of the gymnostom and cheilostom, excretory pore position, postvulval uterine sac length, male and female tail length and morphology, and the length and morphology of the spicules and gubernacula. The occurrence of M. crucis in Spain has, as a result of this study, now also been expanded to a larger area of the southern Iberian Peninsula. Morphological and morphometrical analyses showed that M. canadensis and M. ruehmi are very similar, sharing apomorphic characters. In contrast, M. crucis has plesiomorphic characters. Description, measurements and illustrations are provided for these three species.

Echinococcus granulosus is a helminth from the family Taeniidae, which causes cystic echinococcosis (CE) in humans and diverse livestock around the world. The identification of existing genotypes in different regions is a major step towards the prevention and establishment of control programmes for the disease. This study aimed to detect CE genotypes using polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP) of the internal transcribed spacer-1 (ITS1) gene and sequencing of the cytochrome c oxidase subunit 1 (Cox1) gene in isolates from the central part of Mazandaran province, northern Iran. Forty isolates were collected from sheep, 17 from cattle and 6 from human formalin-fixed paraffin-embedded tissues (FFPE). The ITS1 and Cox1 genes were successfully amplified by PCR in 41 and 42 samples, respectively. PCR-RFLP and sequencing showed that all isolates had the G1–G3 genotypes in this study. Out of 31 isolates subjected to sequencing for the Cox1 gene, 80.7% had the G1 genotype. G2 (16.1%) and G3 (3.2%) genotypes were observed in five sheep and one cattle samples, respectively. Five human isolates were also sequenced for the ITS1 gene, which showed that all samples belonged to the G1 genotype. Ten haplotypes were determined among the isolates by alignment analysis of the Cox1 gene. In summary, this study demonstrated that G1 was the dominant genotype circulating between humans and livestock in the studied region. Furthermore, high genotypic diversity among the CE isolates was observed.

Diagnosis of cystic echinococcosis (CE) is at present mainly based on imaging techniques. Serology has a complementary role, partly due to the small number of standardized and commercially available assays. Therefore we examined the clinical performance of the SERION ELISA classic Echinococcus IgG test. Using 10 U/ml as a cut-off point, and serum samples from 50 CE patients and 105 healthy controls, the sensitivity and specificity were 98.0% and 96.2%, respectively. If patients with other infectious diseases were used as negative controls, the specificity decreased to 76.9%, which causes poor positive predictive values. However, if results between 10 and 15 U/ml are classified as indecisive, the specificity of positive results (≥15 U/ml) increased to 92.5% without greatly affecting the sensitivity (92.0%). Using this approach in combination with imaging studies, the SERION ELISA classic Echinococcosis IgG test can be a useful aid in the diagnosis of CE.

Neurocysticercosis is a parasitic disease caused by encysted larvae of Taenia solium in the human central nervous system. Cysts mainly affect the cerebral hemispheres, although they can also be found in ventricles, basal cisterns, and subarachnoid spaces, and rarely in the cerebellum. Given the impossibility of studying the disease in human patients, Cardona et al. (1999) developed a mouse model of neurocysticercosis, using Mesocestoides corti, a closely related cestode. This allows us to study the parasite–host relationship and the mechanisms involved in the disease, in order to improve the therapy. In this murine model of neurocysticercosis, the location of tetrathyridia in parenchyma, ventricles and meninges has already been reported. The aim of this work is to report the cerebellum as a new location for M. corti tetrathyridia in the murine model of neurocysticercosis. A murine model that reproduces the human pathology is essential to evaluate the symptomatology and response to drug treatment in experimentally infected mice.

The aim of this study was to evaluate the association between eosinophils in ascites and the diagnosis of intestinal anisakidosis in patients with peritoneal signs on physical examination. We reviewed retrospectively 16 patients diagnosed with intestinal anisakidosis, evaluated between 2012 and 2015. All patients had ingested raw anchovies. The analysis of ascites fluid in ten of these patients was compared with that of 15 patients with ascites and other abdominal pathology (except liver cirrhosis). All patients had an increased number of white blood cells in the ascites fluid. The eosinophil count was significantly higher in patients with intestinal anisakidosis (P < 0.01). All patients had a good outcome. Increased eosinophils in ascites fluid is strongly associated with the diagnosis of intestinal anisakidosis.

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.