Molecular phylogeny of the Bothriocephalidea (Cestoda): molecular data challenge morphological classification

ERECTION OF BOTHRIOCESTUS N. GEN. (CESTODA: BOTHRIOCEPHALIDEA) AND REDESCRIPTION OF BOTHRIOCESTUS CUSPIDATUS (COOPER, 1917) (SYN. BOTHRIOCEPHALUS CUSPIDATUS) FROM WALLEYE, SANDER VITREUS, (PERCIFORMES: PERCIDAE) IN NORTH AMERICA

Based on previous molecular phylogenetic analyses, Bothriocestus n. gen. is erected to accommodate bothriocephalid tapeworms that have an elongate scolex, a well-developed apical disc, and a narrow neck region, parasitize freshwater fishes in the Holarctic, and were previously placed in the polyphyletic genus Bothriocephalus Rudolphi, 1808 (Cestoda: Bothriocephalidea). Bothriocestus claviceps (Goeze, 1782) n. comb., a parasite of eels (Anguilla spp.) in the Holarctic region, is designated as the type species. Another species of the new genus, Bothriocestus cuspidatus (Cooper, 1917) (syn. Bothriocephalus cuspidatusCooper, 1917) is redescribed from type and voucher specimens, and new material from the type host, the walleye, Sander vitreus (Mitchill, 1818) (Perciformes: Percidae), in Manitoba and Ontario (where the type locality is located) (Canada) and in New York state and Wisconsin. Bothriocestus cuspidatus of S. vitreus is characterized primarily by the possession of a narrow, long strobila (total length up to 18 cm) composed of distinctly craspedote, trapezoidal proglottids, with primary, secondary, and tertiary proglottids differing in size, and by an arrow-shaped (=cuspidatus) scolex that is distinctly broader than the first proglottids, widest near the base in lateral view and gradually becoming broader toward the anterior end in dorsoventral view. A "dwarf" form of B. cuspidatus (total length of 9-27 mm) from Johnny darter, Etheostoma nigrum Rafinesque, 1820, and tessellated darter, Etheostoma olmstedi Storer, 1842 (both Percidae: Etheostominae), is also characterized morphologically in the present paper.

Review of the metazoan parasites of the economically and ecologically important African sharptooth catfish Clarias gariepinus in Africa: Current status and novel records

One of the most widely distributed African freshwater fish is the African sharptooth catfish Clarias gariepinus (Burchell) that is naturally distributed in 8 of the 10 ichthyofaunal regions of this continent. Clarias gariepinus is a highly valued and cheap staple to local communities and an ideal aquaculture species. Consequently, interest in the parasitic communities of C. gariepinus has increased as parasites may accidentally be ingested by humans when eating uncooked fish or can be introduced into culture systems through fish stocks supplied from local rivers which affect yield, growth, and marketability. This review provides an overview of the ∼107 metazoan parasite species known to parasitise C. gariepinus in Africa and their general life cycles, morphology, paratenic and post-cyclic infections, and the biogeography and validity of records are discussed. A brief overview is included on the application of some of these parasites in environmental studies and their link to human health.

Adding one more to the list: A new species of Eniochobothrium (Cestoda: Lecanicephalidea) from the Oman cownose ray in South Africa

A new species of Eniochobothrium Shipley and Hornell, 1906 was recovered from the Oman cownose ray (Rhinoptera jayakari Boulenger) from the body of water off the south-eastern coastline of the KwaZulu-Natal Province, South Africa. Eniochobothrium acostae n. sp. is described on morphological and molecular grounds. The new species is placed within Eniochobothrium (viz., Eniochobothrium gracile Shipley and Hornell, 1906, Eniochobothrium qatarense Al Kawari, Saoud and Wanas, 1994, Eniochobothrium euaxos Jensen, 2005) by possessing key generic characteristics such as the absence of a vagina, expansion of the anterior region of the strobila forming a trough and presence of a thick-walled cirrus sac. Molecular phylogenetic analyses of the partial 28S rRNA and mtCOI genes confirm the generic characterisation as the newly proposed species groups together with other members of the genus. Eniochobothrium acostae n. sp. currently represents the largest described species of the genus; it possesses slightly fewer testes compared to most congeners, given that this feature has been provided in the original description (e.g., E. euaxos and E. qatarense). The new species of Eniochobothrium is the fourth valid species described to date and the first species record from South African waters.

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A new lecanicephalidean cestode is formally described based on morphological and molecular grounds.

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Molecular phylogenies of ribosomal (partial 28S rRNA) and mitochondrial (mtCOI) genes are provided.

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Molecular phylogenetic analyses placed the new species within the genus Eniochobothrium and support its validity.

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The new species is the fourth species of Eniochobothrium known to date and the first recorded from Southern Africa.

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Given the number of unassessed rhinopterid hosts, several species of Eniochobothrium may await scientific discovery.

Fish tapeworms (Cestoda) in the molecular era: achievements, gaps and prospects

The tapeworms of fishes (Chondrichthyes and Actinopterygii) account one-third (1670 from around 5000) of the total tapeworm (Platyhelminthes: Cestoda) species diversity. In total 1186 species from 9 orders occur as adults in elasmobranchs (sharks, rays and chimaeras), and 484 species from 8 orders mature in ray-finned fishes (referred to here as teleosts). Teleost tapeworms are dominated by freshwater species (78%), but only 3% of elasmobranch tapeworms are known from freshwater rays of South America and Asia (Borneo). In the last 2 decades, vast progress has been made in understanding species diversity, host associations and interrelationships among fish tapeworms. In total, 172 new species have been described since 2017 (149 from elasmobranchs and 23 from teleosts; invalidly described taxa are not included, especially those from the Oriental region). Molecular data, however, largely limited to a few molecular markers (mainly 28S rDNA, but also 18S and cox1), are available for about 40% of fish tapeworm species. They allowed us to significantly improve our understanding of their interrelationships, including proposals of a new, more natural classification at the higher-taxonomy level (orders and families) as well as at the lower-taxonomy level (genera). In this review, we summarize the main advances and provide perspectives for future research.

A NEW SPECIES OF BOTHRIOCEPHALUS (CESTODA: BOTHRIOCEPHALIDAE) FROM LEPOMIS SPP. (ACTINOPTERYGII: CENTRARCHIDAE) IN NORTH AMERICA

Based on morphological and molecular data, a new species of tapeworm, Bothriocephalus kupermani n. sp., is described from pumpkinseed, Lepomis gibbosus (Linnaeus, 1758) (type host), and green sunfish, L. cyanellus Rafinesque, 1819 (Actinopterygii: Centrarchidae) in the United States. The new species differs from its North American congeners mainly in the shape of its scolex, which is almost rectangular in dorsoventral and lateral views (nearly parallel margins in the bothrial region), with shallow, wide bothria, and by an extensive field of vitelline follicles that are also variably present, albeit more sparsely, medially in the cortex of the ovarian and uterine areas. This tapeworm appears to be typically associated with Lepomis sunfishes. Examination of museum specimens of Bothriocephalus species from Lepomis spp. indicates that the tapeworm also parasitizes bluegill, Lepomis macrochirus, longear sunfish, Lepomis megalotis, and that previous records of Bothriocephalus cuspidatus and Bothriocephalus claviceps in these fishes are of the new species, B. kupermani.

Evolutionary transitions of parasites between freshwater and marine environments

Evolutionary transitions of organisms between environments have long fascinated biologists but attention has focused almost exclusively on free-living organisms and challenges to achieve such transitions. This bias requires addressing because parasites are a major component of biodiversity. We address this imbalance by focusing on transitions of parasitic animals between marine and freshwater environments. We highlight parasite traits and processes that may influence transition likelihood (e.g. transmission mode, life cycle, host use), and consider mechanisms and directions of transitions. Evidence for transitions in deep time and at present are described, and transitions in our changing world are considered. We propose that environmental transitions may be facilitated for endoparasites because hosts reduce exposure to physiologically challenging environments and argue that adoption of an endoparasitic lifestyle entails an equivalent transitioning process as organisms switch from living in one environment (e.g. freshwater, seawater, or air) to living symbiotically within hosts. Environmental transitions of parasites have repeatedly resulted in novel forms and diversification, contributing to the tree of life. Recognising the potential processes underlying present-day and future environmental transitions is crucial in view of our changing world and the current biodiversity crisis.

Comparative Characterization of Mitogenomes From Five Orders of Cestodes (Eucestoda: Tapeworms)

The recognized potential of using mitogenomics in phylogenetics and the more accessible use of high-throughput sequencing (HTS) offer an opportunity to investigate groups of neglected organisms. Here, we leveraged HTS to execute the most comprehensive documentation of mitogenomes for cestodes based on the number of terminals sequenced. We adopted modern approaches to obtain the complete mitogenome sequences of 86 specimens representing five orders of cestodes (three reported for the first time: Phyllobothriidea, “Tetraphyllidea” and Trypanorhyncha). These complete mitogenomes represent an increase of 41% of the mitogenomes available for cestodes (61–147) and an addition of 33% in the representativeness of the cestode orders. The complete mitochondrial genomes are conserved, circular, encoded in the same strand, and transcribed in the same direction, following the pattern observed previously for tapeworms. Their length varies from 13,369 to 13,795 bp, containing 36 genes in total. Except for the Trypanorhyncha specimen, the gene order of the other four cestode orders sequenced here suggests that it could be a synapomorphy for the acetabulate group (with a reversion for taenids). Our results also suggest that no single gene can tell all the evolutionary history contained in the mitogenome. Therefore, cestodes phylogenies based on a single mitochondrial marker may fail to capture their evolutionary history. We predict that such phylogenies would be improved if conducted under a total evidence framework. The characterization of the new mitochondrial genomes is the first step to provide a valuable resource for future studies on the evolutionary relationships of these groups of parasites.

LOOP-MEDIATED ISOTHERMAL AMPLIFICATION (LAMP) ASSAY FOR DETECTION OF ASIAN FISH TAPEWORM, SCHYZOCOTYLE ACHEILOGNATHI (YAMAGUTI, 1934) [SYN. BOTHRIOCEPHALUS ACHEILOGNATHI]

The Asian fish tapeworm (Schyzocotyle acheilognathi syn. Bothriocephalus acheilognathi) (AFT) is an invasive parasite that can infect many species of fish, although most hosts are primarily members of Cyprinidae. Pathogenicity has most often been reported in aquaculture settings in fry and fingerling stages of carp (Cyprinus spp.). More recently, it has been shown to cause growth retardation in the endangered bonytail chub (Gila elegans) and found to be widespread in populations of endangered humpback chub (Gila cypha) in the Colorado River, Grand Canyon, Arizona. AFT spreads most often through the transport of infected fish, particularly baitfish. Despite its harmful potential, there is no efficient or accurate ante mortem test to detect AFT in water or fish samples before transport. Herein, we report on the development of a sensitive and specific loop-mediated isothermal amplification (LAMP) assay to detect the parasite in under 30 min from laboratory prepared samples. Six LAMP primers were designed to amplify a variable region of the 18S ribosomal RNA gene in AFT with the detection and quantification of DNA on a real-time fluorometer. The limit of detection was 1 × 101 copies/μl of DNA extracted from as few as 2 AFT eggs. Future application of our assay would be a low-cost test to rapidly and accurately detect AFT DNA from environmental samples on-site so that preventive actions can be taken to halt the spread of the AFT through the movement of infected fish.

Dipylidium caninum draft genome - a new resource for comparative genomic and genetic explorations of flatworms

Here, we present a draft genome of the tapeworm Dipylidium caninum (family Dipylidiidae) and compare it with other cestode genomes. This draft genome of D. caninum is 110 Mb in size, has a repeat content of ~13.4% and is predicted to encode ~10,000 protein-coding genes. We inferred excretory/secretory molecules (representing the secretome), other key groups of proteins (including peptidases, kinases, phosphatases, GTPases, receptors, transporters and ion-channels) and predicted potential intervention targets for future evaluation. Using 144 shared single-copy orthologous sequences, we investigated the genetic relationships of cestodes for which nuclear genomes are available. This study provides first insights into the molecular biology of D. caninum and a new resource for comparative genomic and genetic explorations of this and other flatworms.

Ex Uno Plures? Morphotype and Lineage Diversity of Bothriocephalus (Cestoda: Bothriocephalidea) in North American Freshwater Fishes

Morphological and molecular evaluation of tapeworms of the genus Bothriocephalus Rudolphi, 1808 (Cestoda: Bothriocephalidea), based on newly collected and uniformly fixed worms from freshwater fishes in Canada and the United States has revealed unexpected diversity. With a combination of selected morphological features and 4 molecular markers (18S rDNA V8 region, ITS1, ITS2, and COI gene sequences), the following morphotypes and lineages of the Bothriocephalus cuspidatus Cooper, 1917 complex were identified, several of which are specific to their respective fish definitive hosts and may represent separate species: B. cuspidatus sensu stricto from walleye, Sander vitreus (type host), which likely includes a miniature morphotype from Johnny darter, Etheostoma nigrum (both Percidae); Bothriocephalus morphotype from pumpkinseed, Lepomis gibbosus (Centrarchidae); and Bothriocephalus morphotype from rock bass, Ambloplites rupestris (Centrarchidae). The Bothriocephalus morphotype from goldeye, Hiodon alosoides (Hiodontidae), may also represent a separate lineage (possibly Bothriocephalus texomensisSelf, 1954) but requires additional studies. A morphotype from smallmouth bass, Micropterus dolomieu, based on a single specimen, is morphologically and genetically very similar to the morphotype from rock bass. Morphological study of the scolex and strobila of heat-killed and fixed specimens has revealed consistent differences, often subtle, that allowed us to differentiate between these morphotypes.

Ultrastructure of the uterus, embryonic envelopes and the coracidium of the enigmatic tapeworm Tetracampos ciliotheca (Cestoda: Bothriocephalidea) from African sharptooth catfish (Clarias gariepinus)

Transmission electron microscopy (TEM) was used to study the ultrastructure of the uterus and egg morphology in the enigmatic bothriocephalidean tapeworm Tetracampos ciliotheca. The uterine wall, underlain by well-developed muscle bundles, consists of a syncytial epithelium which is characterized by the abundance of free ribosomes, mitochondria and cisternae of granular endoplasmic reticulum (GER). On the apical surface of the uterine epithelium, there is an abundant network of cytoplasmic microlamellae projecting into the uterine lumen. The lumen is filled with freely lying eggs which are located close to the uterine wall but do not contact with the microlamellae of the uterine epithelium. The developed eggs possess an oncosphere surrounded by four envelopes: (1) a thin egg shell; (2) an outer envelope; (3) a syncytial, ciliated inner envelope; and (4) the oncospheral membrane. The mature hexacanth is armed with three pairs of oncospheral hooks, as well as somatic and hook muscles and five types of cells (1) binucleated subtegumental cell, (2) somatic cells, (3) penetration gland cells, (4) nerve cells and (5) germinative cells. Considering the relative scarcity of descriptive and comparative studies on the ultrastructure of the uterus and egg morphology in the order Bothriocephalidea, we concluded that Tet. ciliotheca displays a unique type of egg development. Based on these results, we discuss plausible ideas relating to the function of these structures for consideration in future studies.

A study of the endohelminths of the European perch Perca fluviatilis L. from the central region of the Danube river basin in Slovakia

The European perch Perca fluviatilis L. serves as a host of different endohelminths of Trematoda, Cestoda, Nematoda, and Acanthocephala. Its natural range covers freshwater basins throughout much of Europe, including the Danube. Since information about endohelminths of European perch from this international river basin has been rather sporadic, the parasitological examinations of 700 perch from the central region of the Danube river basin in Slovakia were performed in October 2017 and April 2018. The larval stages of Triaenophorus nodulosus (Cestoda) were found in cysts located in the perch liver and adults of Proteocephalus percae (Cestoda) were isolated from the intestine. The larval stages of Eustrongylides sp. (Nematoda) and metacercariae of Clinostomum complanatum (Trematoda), both potential causative agents of fish-borne zoonoses, were found in the musculature. Spatial and seasonal differences in the occurrence of currently detected helminths were discussed with data on biological and environmental conditions of particular sampling site.

Endohelminths of European Perch (Perca fluviatilis) from Selected Localities in Poland with an Emphasis on Search of the Broad Fish Tapeworm Dibothriocephalus latus

INTRODUCTION

A piscivorous fish European perch (Perca fluviatilis) is present in all types of lakes and brackish waters in Poland. Previous ichthyoparasitological surveys revealed broad spectrum of endohelminths in perch from different aquatic environments. Among them, detection of Diphyllobothrium sp. and Dibothriocephalus latus (syn. Diphyllobothrium latum) in the Pomeranian Bay is of particular interest, since D. latus is one of the causative agents of diphyllobothriasis, fish-borne parasitic zoonosis. Besides, D. latus eggs were previously detected in coprological samples of otter, wolf and lynx from the Białowieża Primeval Forest.

AIM

To conduct parasitological examinations of European perch from the Pomeranian Bay in order to detect the spectrum of its endohelminths and to provide a pilot study on helminths of perch from different water bodies in the Białowieża Primeval Forest. Due to zoonotic character of D. latus, we have focused our attention to this tapeworm.

RESULTS

The larvae of tapeworm Triaenophorus nodulosus and thorny-headed worm Acanthocephalus lucii were detected in perch from the Pomeranian Bay. In perch from different localities in the Białowieża Primeval Forest, T. nodulosus, A. lucii and tapeworm Proteocephalus percae were detected. D. latus plerocercoids were found neither in musculature nor in peritoneal cavity and other internal organs of any of the fish examined from both studied localities in Poland.

CONCLUSION

Future screening implementing morphological and molecular markers is needed in order to understand the current distribution of D. latus in Europe.

Diversity and phylogenetic relationships of European species of Crepidostomum Braun, 1900 (Trematoda: Allocreadiidae) based on rDNA, with special reference to Crepidostomum oschmarini Zhokhov & Pugacheva, 1998

BACKGROUND

Within the genus Crepidostomum Braun, 1900, identification of species and taxonomic decisions made only on the basis of adult morphology have resulted in great problems associated with evaluating actual diversity and validity of species. Life-cycle data, while equal in importance to adult characters, are scarce, controversial or incomplete for most Crepidostomum spp. In this study, rDNA sequences generated from adult and larval Crepidostomum spp. and some other allocreadiid species were analysed to reveal the diversity and phylogenetic relationships of the species and their host range. Detailed morphological description based on light microscopy, SEM tegumental surface topography and genetic data are provided for the poorly known trematode C. oschmarini Zhokhov & Pugacheva, 1998 found in the intestine of two teleost fish species, Barbatula barbatula (L.) and Cottus gobio L.

RESULTS

We characterized 27 isolates of adult and larval parasites. Based on newly obtained 28S and ITS1-5.8S-ITS2 rDNA sequences, new intermediate and final hosts were ascertained, and life-cycles clarified for some allocreadiids. New knowledge on the diversity and phylogenetic relationships of European Crepidostomum spp. was gained. The validity of C. oschmarini was verified based on comparative sequence analysis. Ophthalmoxiphidiocercariae of C. oschmarini were recorded in sphaeriid bivalves Pisidium (Euglesa) casertanum (Poli). Additionally, morphological differences between gravid specimens of C. oschmarini and other related species were observed.

CONCLUSIONS

Species of the Allocreadiidae parasitizing fishes in Europe are distributed among two monophyletic genera, Allocreadium and Bunodera, and two paraphyletic Crepidostomum clades. A complex of Crepidostomum metoecus (syn. C. nemachilus), C. oschmarini and Crepidostomum sp. 2 clustered in one clade, and a complex of C. farionis, Crepidostomum sp. 1 and, probably, C. wikgreni in the other. Molecular data indicated that C. oschmarini and Crepidostomum sp. 2 presumably have a wide geographical distribution in Europe. The new data provided evidence that Crepidostomum is a more diverse genus than can be judged from morphological data and host switching in this genus may occur independently of fish-host phylogeny.

First record of the invasive tapeworm, Schyzocotyle acheilognathi (Pseudophyllidea; Bothriocephalidae) in native freshwater fish, Brazil

Schyzocotyle acheilognathi is a tapeworm cestode commonly found in native freshwater fishes from Asia. This cestode has low host specificity and for that reason it has been registered parasitizing more than 200 cultured and wild fish species, besides amphibians, reptiles and birds from different regions of the world. With a high pathogenic potential, S. acheilognathi may cause mortalities in highly infected fish. In South America, Schyzocotyle was reported in Cyprinus carpio from a Brazilian fish farm at the municipality of Cornélio Procópio, northern Paraná State and from the natural environment in C. carpio from Neuquen River, Patagonia, Argentina. So far, there has been no report of this parasite in South American native fishes. Herein we report the first occurrence of the invasive tapeworm S. acheilognathi in Rineloricaria pentamaculata (Siluriformes, Loricariidae), a native armored freshwater catfish from southern Brazil.

Trace element biomineralisation in the carapace in male and female Argulus japonicus

Parasites of fishes have been shown to be effective bioindicators of the aquatic environment. Few investigations have been conducted on ectoparasite models and therefore little is known about the fate of trace elements and metals which they accumulate. In this study trace element sequestration was observed in the carapace of the fish louse, Argulus japonicus and found to relate to the sex of the parasite, as well as, the degree of sclerotization of the carapace. Adults of A. japonicus were collected from cyprinid hosts in the Vaal Dam, South Africa. Parasites were removed and flash frozen in liquid nitrogen before being sectioned with a cryomicrotome. Sections and whole mounts of parasites were prepared and treated with Phen–Green ^TM FL cell–permeant diacetate. Cryosections were assessed for trace elements and metals using a scanning electron microscope equipped with energy dispersive spectroscopy. Results indicated that in both male and female parasites, trace elements become bound to the carapace and produce more intense fluorescence than in soft tissues. Sexual dimorphic differences were further observed between male and female parasites. The intensity of the fluorescence signals was greater in the carapace of male parasites than in females, particularly when comparing the carapace of the ventral side of the thorax. In females, an amorphous layer of material surrounding the eggs was observed and produced an intense fluorescent signal. Levels of trace elements and metals detected were not significantly different between male and female parasites. Results observed serve as a demonstration for the first time of trace element sequestration in a freshwater crustacean parasite and possible mechanisms employed to reduce body burdens of trace elements and metals.

Asian Fish Tapeworm: The Most Successful Invasive Parasite in Freshwaters

The Asian fish tapeworm (AFT), Schyzocotyle acheilognathi, is a notorious and highly successful invasive parasite reported in a wide spectrum of freshwater fishes, and new reports of its spread continue to emerge. To date, no thorough review of its worldwide distribution and host associations is available. In the present work, we collected information from 651 articles up until 2017, from which we updated the number of the hosts to 312 fish species and 11 non-fish species, which is quite unusual among helminths. The AFT has spread to all but one continent (Antarctica). The highest number of records are from North America, followed by Asia and Europe. A key feature of its invasive success is its broad environmental tolerance.

The First Record of the Invasive Asian Fish Tapeworm (Schyzocotyle Acheilognathi) from An Endemic Cichlid Fish in Madagascar

The Asian fish tapeworm, Schyzocotyle acheilognathi (Yamaguti, 1934) (Cestoda: Bothriocephalidea), is an invasive parasite of freshwater fishes that have been reported from more than 200 freshwater fish worldwide. It was originally described from a small cyprinid, Acheilognathus rombeus, in Japan but then has spread, usually with carp, minnows or guppies, to all continents including isolated islands such as Hawaii, Puerto Rico, Cuba or Sri Lanka. In the present account, we report the first case of the infection of a native cichlid fish, Ptychochromis cf. inornatus (Perciformes: Cichlidae), endemic to Madagascar, with S. acheilognathi. The way of introduction of this parasite to the island, which is one of the world's biodiversity hotspots, is briefly discussed.

Tapeworm chromosomes: their value in systematics with instructions for cytogenetic study

The history and value of cytogenetic features for addressing questions of the evolution and systematics of tapeworms (Cestoda) are briefly reviewed along with instructions for collecting karyological data. As a supplement to worm morphology, chromosome number and morphology have been helpful in determining the systematic status of some genera in the Diphyllobothriidae and species in the Bothriocephallidea. In addition, many new techniques for chromosome analysis have been recently applied in morphological and molecular studies of invertebrates, including tapeworms. Methods of molecular karyology, fluorescence in situ hybridisation, and chromosomal location of satellite DNA, microsatellites or histone genes may also provide useful data to inference of taxonomic relationships and for revealing trends or general lines of chromosome evolution. However, as karyological data are available only for few tapeworms, they are seldom an integral part of evolutionary and taxonomic studies of cestodes. A primary reason for this lack of karyological data may lie in general difficulties in working with tapeworm chromosomes. To address these problems, herein we present a well-tested, step-by-step illustrated guide on the fixation of tapeworm material and preparation of their chromosomes for cytogenetic studies. The technique requires standard glassware, few reagents and simple equipment such as needles; it can also be used on other neodermatan flatworms.

Parasites and pollution: the effectiveness of tiny organisms in assessing the quality of aquatic ecosystems, with a focus on Africa

The aquatic environment represents the final repository for many human-generated pollutants associated with anthropogenic activities. The quality of natural freshwater systems is easily disrupted by the introduction of pollutants from urban, industrial and agricultural processes. To assess the extent of chemical perturbation and associated environmental degradation, physico-chemical parameters have been monitored in conjunction with biota in numerous biological monitoring protocols. Most studies incorporating organisms into such approaches have focussed on fish and macroinvertebrates. More recently, interest in the ecology of parasites in relation to environmental monitoring has indicated that these organisms are sensitive towards the quality of the macroenvironment. Variable responses towards exposure to pollution have been identified at the population and component community level of a number of parasites. Furthermore, such responses have been found to differ with the type of pollutant and the lifestyle of the parasite. Generally, endoparasite infection levels have been shown to become elevated in relation to poorer water quality conditions, while ectoparasites are more sensitive, and exposure to contaminated environments resulted in a decline in ectoparasite infections. Furthermore, endoparasites have been found to be suitable accumulation indicators for monitoring levels of several trace elements and metals in the environment. The ability of these organisms to accumulate metals has further been observed to be of benefit to the host, resulting in decreased somatic metal levels in infected hosts. These trends have similarly been found for host-parasite models in African freshwater environments, but such analyses are comparatively sparse compared to other countries. Recently, studies on diplozoids from two freshwater systems have indicated that exposure to poorer water quality resulted in decreased infections. In the Vaal River, the poor water quality resulted in the extinction of the parasite from a site below the Vaal River Barrage. Laboratory exposures have further indicated that oncomiracidia of Paradiplozoon ichthyoxanthon are sensitive to exposure to dissolved aluminium. Overall, parasites from African freshwater and marine ecosystems have merit as effect and accumulation indicators; however, more research is required to detail the effects of exposure on sensitive biological processes within these organisms.

First Freshwater Bothriocephalidean (Cestoda) from Tropical South America, Closely Related to African Taxa

Regobothrium microhamulinum n. gen. and n. sp. (Bothriocephalidea: Bothriocephalidae) is proposed to accommodate a new cestode from flatfish Catathyridium jenynsii (Chabanaud, 1922) (Pleuronectiformes: Acharidae; type host) and another 3 freshwater fishes of the orders Characiformes, Cyprinodontiformes, and Siluriformes in the Neotropical Region. The new genus is placed in the Bothriocephalidae because it possesses medioventral uterine and mediodorsal genital pores and a follicular vitellarium. Regobothrium n. gen. is characterized by possessing a tiny, slightly subovate scolex narrower than the strobila, with an apical disc armed with 2 semicircles of 15-17 tiny hooks in each and an acraspedote strobila. Regobothrium n. gen. differs from all bothriocephalid cestodes that have a scolex armed with hooks by their small size (maximum length less than 20 μm) and a triangular shape with the basal part (handle or basal plate) shorter than the distal coniform part (blade). In the other hooked bothriocephalids, hooks have a longer handle than a blade. Regobothrium microhamulinum n. gen. and n. sp. is the third bothriocephalidean cestode described from freshwater teleosts in South America but the first out of Patagonia. Molecular phylogenetics consider Regobothrium as a member of a lineage consisting of (up to now exclusively) freshwater bothriocephalids from the Ethiopian biogeographic region, thus indicating Gondwanan relationship.

Update on the distribution of the co-invasive Schyzocotyle acheilognathi (= Bothriocephalus acheilognathi), the Asian fish tapeworm, in freshwater fishes of Mexico

The Asian fish tapeworm, Schyzocotyle acheilognathi (syn. Bothriocephalus acheilognathi) represents a threat to freshwater fish, mainly cyprinids, across the globe. This tapeworm possesses an extraordinary ability to adapt to different environmental conditions and, because of that, from its natural geographical origin in mainland Asia, it has colonized every continent except Antarctica. It is thought that this pathogenic tapeworm was first co-introduced into Mexico in 1965 from China, with the grass carp Ctenopharyngodon idella, although the first formal record of its presence was published in 1981. Over the past 35 years, the Asian fish tapeworm has invaded about 22% of the freshwater fish in Mexico. Because fish communities in Mexico are characterized by high species richness and levels of endemism, S. acheilognathi is considered as a co-introduced and co-invasive species. In this review, we update the geographic distribution and host spectrum of the Asian fish tapeworm in Mexico. Up until December 2016, the tapeworm had been recorded in 110 freshwater fish species (96 native and 14 introduced), included in 51 genera, 11 families and 4 orders; it was also widely distributed in all types of aquatic environments, and has been found in 214 localities. We present novel data from a survey aimed at establishing the distribution pattern of the tapeworm in native freshwater fishes of two rivers in north-central Mexico, and the genetic variation among individuals of this co-invasive species collected from different host species and localities. We discuss briefly the factors that have determined the remarkable invasive success of this parasite in freshwater systems in Mexico.

Trace element and metal sequestration in vitellaria and sclerites, and reactive oxygen intermediates in a freshwater monogenean, Paradiplozoon ichthyoxanthon

Exposure to metals and other trace elements negatively affects infection dynamics of monogeneans, including diplozoids, but, physiological mechanisms linked to exposure have yet to be documented. In this study sequestration of trace elements and reactive oxygen intermediate production in the monogenean, Paradiplozoon ichthyoxanthon, was demonstrated. During dissection of host fish, Labeobarbus aeneus, the gills were excised and assessed for P. ichthyoxanthon, which were removed and frozen for fluorescence microscopy or fixed for transmission electron microscopy. Trace elements were sequestered in the vitellaria and sclerites in P. ichthyoxanthon, and the presence of reactive oxygen intermediates was observed predominantly in the tegument of the parasite. Trace elements and metals identified and ranked according to weight percentages (wt%) in the vitellaria were Cu > C > Au > O > Cr > Fe > Si while for the sclerites C > Cu > O > Au > Fe > Cr > Si were identified. For most element detected, readings were higher in the vitellaria than the sclerites, except for C and O which were higher in sclerites. Specifically for metals, all levels detected in the vitellaria were greater than in sclerites. Based on the proportion of trace elements present in the vitellaria and sclerites it appears that most trace elements including metals were sequestered in the vitellaria. The results of reactive oxygen intermediate production in the tegument of the parasite suggests either trace element accumulation takes place across the tegument or results from the action of the host's immune response on the parasite. The results serve as the first demonstration of trace element sequestration and reactive oxygen intermediates in a freshwater monogenean parasite.

Annotated checklist of fish cestodes from South America

An exhaustive literature search supplemented by a critical examination of records made it possible to present an annotated checklist of tapeworms (Cestoda) that, as adults or larvae (metacestodes), parasitize freshwater, brackish water and marine fishes, i.e. cartilaginous and bony fishes, in South America. The current knowledge of their species diversity, host associations and geographical distribution is reviewed. Taxonomic problems are discussed based on a critical evaluation of the literature and information on DNA sequences of individual taxa is provided to facilitate future taxonomic and phylogenetic studies. As expected, the current knowledge is quite uneven regarding the number of taxa and host-associations reported from the principal river basins and marine ecoregions. These differences may not only reflect the actual cestode richness but may also be due to the research effort that has been devoted to unravelling the diversity of these endoparasitic helminths in individual countries. A total of 297 valid species, 61 taxa identified to the generic level, in addition to unidentified cestodes, were recorded from 401 species of fish hosts. Among the recognized cestode orders, 13 have been recorded in South America, with the Onchoproteocephalidea displaying the highest species richness, representing c. 50% of all species diversity. The majority of records include teleost fish hosts (79%) that harbour larval and adult stages of cestodes, whereas stingrays (Myliobatiformes) exhibit the highest proportion of records (39%) among the elasmobranch hosts. Fish cestodes are ubiquitous in South America, being mostly recorded from the Warm Temperate Southeastern Pacific (WTSP; 31%) for marine hosts and the Amazon River basin (45%) for freshwater ones. The following problems were detected during the compilation of literary data: (i) unreliability of many records; (ii) poor taxonomic resolution, i.e. identification made only to the genus or even family level; (iii) doubtful host identification; and (iv) the absence of voucher specimens that would enable us to verify identification. It is thus strongly recommended to always deposit representative specimens in any type of studies, including faunal surveys and ecological studies. An analysis of the proportion of three basic types of studies, i.e. surveys, taxonomic and ecological papers, has shown a considerable increase of ecological studies over the last decade.

The complete mitochondrial genome of a parasitic flatworm Senga ophiocephalina (Cestoda: Bothriocephalidae)

Mitochondrial DNA of nematodes undergoes frequent rearrangements, so it is a very good model for studying the mitochondrial genome evolution. The complete mitochondrial genome of a parasitic nematode Senga ophiocephalina was sequenced and annotated. The 13,816 bp-long genome contained 12 protein-coding genes (atp8 gene was missing), two ribosomal RNAs, 22 transfer RNAs, and a 391 bp non-coding region. Phylogenetic analysis showed that S. ophiocephalina forms a monophyletic cluster with the remaining two Bothriocephalidae species.

When proglottids and scoleces conflict: phylogenetic relationships and a family-level classification of the Lecanicephalidea (Platyhelminthes: Cestoda)

This study presents the first comprehensive phylogenetic analysis of the interrelationships of the morphologically diverse elasmobranch-hosted tapeworm order Lecanicephalidea, based on molecular sequence data. With almost half of current generic diversity having been erected or resurrected within the last decade, an apparent conflict between scolex morphology and proglottid anatomy has hampered the assignment of many of these genera to families. Maximum likelihood and Bayesian analyses of two nuclear markers (D1-D3 of lsrDNA and complete ssrDNA) and two mitochondrial markers (partial rrnL and partial cox1) for 61 lecanicephalidean species representing 22 of the 25 valid genera were conducted; new sequence data were generated for 43 species and 11 genera, including three undescribed genera. The monophyly of the order was confirmed in all but the analyses based on cox1 data alone. Sesquipedalapex placed among species of Anteropora and was thus synonymized with the latter genus. Based on analyses of the concatenated dataset, eight major groups emerged which are herein formally recognised at the familial level. Existing family names (i.e., Lecanicephalidae, Polypocephalidae, Tetragonocephalidae, and Cephalobothriidae) are maintained for four of the eight clades, and new families are proposed for the remaining four groups (Aberrapecidae n. fam., Eniochobothriidae n. fam., Paraberrapecidae n. fam., and Zanobatocestidae n. fam.). The four new families and the Tetragonocephalidae are monogeneric, while the Cephalobothriidae, Lecanicephalidae and Polypocephalidae comprise seven, eight and four genera, respectively. As a result of their unusual morphologies, the three genera not included here (i.e., Corrugatocephalum, Healyum and Quadcuspibothrium) are considered incertae sedis within the order until their familial affinities can be examined in more detail. All eight families are newly circumscribed based on morphological features and a key to the families is provided. Aspects of morphological evolution and host associations are discussed in a phylogenetic context for each family and for the order as a whole. Lecanicephalidean genera lacking apical structures were confirmed as the earliest diverging lineages. Proglottid anatomy was determined to be much more conserved and indicative of phylogenetic affinities than scolex morphology. Collectively, the Lecanicephalidea parasitize three of the four orders of Batoidea-their almost exclusive absence from skates (Order Rajiformes) appears to be real; only a few records from sharks exist. At the family level, the breadth of host associations is correlated with taxonomic diversity of the family. The degree to which factors such as intermediate host use or host specificity at any stage in the life-cycle shape these patterns is currently unknown.