Taxonomy of Physaloptera mirandai (Nematoda: Physalopteroidea) based in three-dimensional microscopy and phylogenetic positioning

Investigating parasites in three dimensions: trends in volume microscopy

To best understand parasite, host, and vector morphologies, host-parasite interactions, and to develop new drug and vaccine targets, structural data should, ideally, be obtained and visualised in three dimensions (3D). Recently, there has been a significant uptake of available 3D volume microscopy techniques that allow collection of data across centimetre (cm) to Angstrom (Å) scales by utilising light, X-ray, electron, and ion sources. Here, we present and discuss microscopy tools available for the collection of 3D structural data, focussing on electron microscopy-based techniques. We highlight their strengths and limitations, such that parasitologists can identify techniques best suited to answer their research questions. Additionally, we review the importance of volume microscopy to the advancement of the field of parasitology.

Morphology and genetic characterization of Physaloptera sibirica Petrow & Gorbunov, 1931 (Spirurida: Physalopteridae), from the hog-badger Arctonyx collaris Cuvier (Carnivora: Mustelidae), with molecular phylogeny of Physalopteridae

BACKGROUND

Nematodes of the family Physalopteridae (Spirurida: Physalopteroidea) commonly parasitize the alimentary canal of all major vertebrate groups. However, many physalopterid species are not adequately described, especially regarding the detailed morphology of the cephalic end. The current genetic database for Physaloptera species is still very limited, which seriously hampers molecular-based species identification. Additionally, the systematic status of some genera and the evolutionary relationships of the subfamilies in the Physalopteridae remain under debate.

METHODS

New morphological data for Physaloptera sibirica was gathered using light and scanning electron microscopy based on newly collected specimens from the hog badger Arctonyx collaris Cuvier (Carnivora: Mustelidae) in China. Six different genetic markers, including nuclear small ribosomal DNA (18S), large ribosomal DNA (28S) and internal transcribed spacer (ITS), mitochondrial cytochrome c oxidase subunit 1 (cox1) and subunit 2 (cox2), and the 12S small subunit ribosomal RNA gene of P. sibirica were sequenced and analyzed for the first time to our knowledge. Additionally, to construct a basic molecular phylogenetic framework for the Physalopteridae, phylogenetic analyses were performed based on the cox1 and 18S + cox1 genes using maximum likelihood (ML) and Bayesian inference (BI) methods.

RESULTS

Scanning electron microscopy (SEM) observation displayed the details of the cephalic structures, deirids, excretory pore, caudal papillae, vulva, phasmids and egg of P. sibirica for the first time to our knowledge. Pairwise comparison of the sequences obtained for P. sibirica did not reveal intraspecific divergence regarding the 18S, 28S, cox1 and 12S genetic markers and a low level of divergence in the ITS (0.16%) and cox2 (2.39%) regions. Maximum likelihood and Bayesian inference analyses showed that the representatives of Physalopteridae formed two major clades (species of Physalopterinae + Thubunaeinae parasitic in terrestrial vertebrates and Proleptinae only occurring in marine or freshwater fishes). Turgida turgida was found nested among representatives of Physaloptera. Physaloptera sibirica clustered together with P. rara. Physalopteroides sp. (Thubunaeinae) formed a sister relationship to the physalopterine Abbreviata caucasica.

CONCLUSIONS

Physaloptera sibirica was redescribed, which is the fourth nematode parasite reported from the hog badger A. collaris, and A. collaris represents a new host for P. sibirica. The phylogenetic results challenged the validity of the subfamily Thubunaeinae and of the genus Turgida and supported dividing the family Physalopteridae into two subfamilies, Physalopterinae and Proleptinae. However, we do not make any immediate systematic changes in the Physalopteridae, because a more rigorous study with broader representation of the Physalopteridae is required. These present findings contribute to morphologically identifying P. sibirica more accurately and provide new insights into the systematics of the Physalopteridae.

“Revisiting the past”: a redescription of Physaloptera retusa (Nemata, Physalopteridae) from material deposited in museums and new material from Amazon lizards

Abstract Physaloptera Rudolphi, 1819 is a genus of nematodes that includes approximately 100 species parasitic in vertebrates around the world. From these, approximately 30 occur in the Neotropical region, with nine reported from neotropical reptiles. Physaloptera spp. are recognized by their distinct morphology of the apical end and characters of the reproductive system. However, despite the fact that the morphological characters for species diagnosis have been firmly established, we frequently find identification problems regarding poorly detailed descriptions and poorly preserved specimens. These may lead to taxonomic incongruencies. Physaloptera retusa (Rudolphi, 1819) is the most common species of the genus and has been reported from several species of neotropical reptiles. Based on our reexaminations of nematode specimens identified as P. retusa from different museum collections, we provide a detailed redescription including the type material, voucher specimens and new specimens recovered currently and showed in this study with new morphological data obtained using light and scanning electron microscopy tools.

Morphological and molecular characterization of Paraleptus chiloscyllii Yin & Zhang, 1983 (Nematoda: Physalopteridae) from the brownbanded bambooshark Chiloscyllium punctatum Müller & Henle (Elasmobranchii: Orectolobiformes)

Paraleptus (Spirurida: Physalopteridae) is a small genus of nematodes, parasitic in fishes, most species of which are inadequately described. Genetic data for these congeners have not been reported. The detailed morphology of P. chiloscyllii was studied using light and scanning electron microscopy, based on newly collected specimens from the brownbanded bambooshark C. punctatum Müller & Henle (Elasmobranchii: Orectolobiformes) in the Taiwan Strait. Some previously unreported morphological features of taxonomic significance were observed, i.e., pseudolabium with two sublateral rows of 6-7 small spines, 7-8 small spines on each lower rim between pseudolabia, deirids not distally bifurcated, vulva with remarkable protruding lip, presence of 1 pair medio-ventral precloacal papillae and 1 pair of discoid protrusions of postcloacal lip in male. The specimens described by González-Solís & Ali's (2015) as P. chiloscyllii from the Arabian carpetshark C. arabicum off Iraq are considered a new species, for which the name P. moraveci n. sp. is proposed. The genetic characterization of the partial small (18S) and large (28S) ribosomal DNA, and the partial mitochondrial cytochrome c oxidase subunit 1 (cox1) of P. chiloscyllii are provided for the first time. There was no intraspecific nucleotide divergence detected in the 18S and 28S regions among different individuals of P. chiloscyllii, but a low level of intraspecific genetic variation was found in the cox1 (0.62-0.92%). The present genetic data is very important for molecular identification, and will be valuable for further invertigantions on the population genetics and phylogeny of this group.

First study on the helminth community structure of the neotropical marsupial Metachirus myosuros (Didelphimorphia, Didelphidae)

Metachirus myosuros is a marsupial species widely distributed in South America. Despite this, there is a lack of knowledge about its helminth parasites and helminth community structure. The aims of this study were to describe the species composition and determine the parasitological parameters of helminth communities of M. myosuros in preserved areas of the Atlantic Forest, Igrapiúna, Bahia state, northeastern Brazil. Parasites were searched from 19 specimens of this marsupial (18 were infected with at least one species), counted and identified. Ten species of helminth parasites were obtained: 7 nematodes, 2 platyhelminths and 1 acanthocephalan. The most abundant species were Aspidodera raillieti, Cruzia tentaculata, Physaloptera mirandai and Viannaia conspicua (Nematoda). These species were also the only dominant ones in the component community. Male hosts had higher prevalence of P. mirandai and greater abundance of V. conspicua. We observed a relationship between host body size and helminth abundance in both male and female hosts, and between host body size and helminth species richness in female hosts. This was the first study to analyze the helminth fauna and helminth community structure of M. myosuros. This was the first report of occurrences of A. raillieti and Didelphonema longispiculata in M. myosuros.

Additional characterization of the adult worm Mammomonogamus laryngeus (Railliet, 1899) and the tissue lesions caused by the infection in buffaloes

Mammomonogamus spp. are parasites with curious characteristics, such as the "Y" shape that results from male and female maintaining the permanent copulation position and the controversial presence or absence of spicules. These nematodes are hematophagous and cause damage to the upper respiratory tracts of cattle, sheep, goats, deer, wild yaks, and orangutans. Human infection is rare and most cases until now have been in the Caribbean Islands or in Brazil, and mainly in farmworkers but recently there have been reports affecting tourists. In the present work, the parasites were recovered from the laryngopharynx and larynx region of Bubalus bubalis on the island of Marajó, Pará, Brazil. Different microscopy methodologies were applied (bright field, fluorescence, and scanning electron microscopy) to explore the ultrastructural details of the anterior end, genital structures and the host tissue damage caused by the nematodes. The well-developed mouth is an important structure in the identification of these nematodes and used by the parasite to adhere to the host's tissue. Different methodologies in microscopy and molecular biology contributed to a detailed morphological description and showed the phenotypic position of Mammomonogamus laryngeus. Light and scanning electron microscopy (SEM) showed details of the papillae, amphids, festoons, ribs, and teeth. Fluorescence microscopy enabled a detailed characterization of different structures, such as the bursal rays and SEM enabled the visualization of the specialized features of the cuticle surface in the male and female. Histopathological analyses, cryofracture and environmental SEM experiments of the infected tissues were carried out in order to investigate the lesions resultant from the parasitism. In addition, the parasite couples were submitted to cryofracture and these results revealed details of the reproductive structures of both sexes, including the male spicule.

Eurytrema coelomaticum: updated morphology of adult worms using advanced microscopy experiments

Eurytrema coelomaticum is a digenean flatworm of ruminants that is the causative agent of eurytrematosis, a disease of veterinary health concern. Although modern techniques of morphological analysis have provided new insights about the morphology and anatomy of parasitic helminths, most studies on E. coelomaticum adults are based on conventional light microscopy. In the present study, a combined approach using brightfield, fluorescence, confocal and scanning electron microscopies (SEMs), together with the cryofracture technique, have updated morphological data on E. coelomaticum recovered from cattle in Rio de Janeiro State, Brazil. Light microscopy confirmed the presence of several structures present in the current description, such as suckers, pharynx, oesophagus, intestinal bifurcation and the cirrus-sac. Fluorescence stereomicroscopy revealed for the first time the cubic crystal protein inclusions in the forebody, which were further detailed by confocal and SEMs. Confocal microscopy provided detailed information of the muscular architecture associated with the attachment structures (suckers), digestive system (pharynx and oesophagus), egg-forming complex (ovary, Mehlis' gland and Laurer's canal) and male reproductive system, which are similar to those found in other digenean flukes. SEM images of cryofractured parasites showed mucus and developing eggs within uterine loops. It was demonstrated that the combination of advanced tools generated complementary information, confirming the importance of experimental morphology in parasitology. Therefore, the knowledge of the adult structural organization of E. coelomaticum was improved and this work has contributed to propose new morphological criteria to evaluate the effects of antiparasitic drugs on flukes of medical and veterinary importance.