Myxozoan infections of caecilians demonstrate broad host specificity and indicate a link with human activity

Synopsis of myxosporean species (Cnidaria: Myxozoa) parasitizing fishes from Vietnam

This paper provides an updated checklist of species-level identified myxosporeans from marine and freshwater fishes in Vietnam. The list includes 51 nominal species (38 marine and 13 freshwater) belonging to 9 genera: Myxobolus Bütschli, 1882 (26 species); Kudoa Meglitsch, 1947 (6 species); Henneguya Thélohan, 1892 (6 species); Thelohanellus Kudo, 1933 (5 species); Unicapsula Davis, 1924 (2 species); Ceratomyxa Thélohan, 1892 (2 species), Zschokkella Auerbach, 1909 (2 species); Auerbachia Meglitsch, 1960 (1 species), and Meglitschia Kovaleva, 1988 (1 species). For each parasite species, information on myxospore morphology, line drawings, fish hosts, infection sites, and collection locality in Vietnam are reported. Where available, we also provide GenBank accession numbers for nucleotide sequence data. In addition, taxonomic status of several species was discussed and Myxobolus eszterbaueri nom. nov. is proposed as a junior homonym for Myxobolus hakyi Baska, Voronin, Eszterbauer, Müller, Marton & Molnár 2009, which is preoccupied.

Description of Myxobolus hoabinhensis n. sp. (Myxosporea: Myxobolidae), infecting the trunk muscles of goldfish Carassius auratus (Linnaeus, 1758) (Cypriniformes: Cyprinidae) in northern Vietnam

During a survey of myxosporean parasites of freshwater fishes in northern Vietnam, myxospores resembling those of the genus Myxobolus (Myxosporea: Myxobolidae) were found in the trunk muscle of 6 out of 35 specimens (17.14%) of wild goldfish Carassius auratus (Cypriniformes: Cyprinidae). The mature spores were 12.0 ± 0.4 (11.4 - 12.6) µm long, 8.5 ± 0.2 (7.9 - 9.0) µm wide and 6.1 ± 0.2 (5.8 - 6.3) µm thick, containing two pyriform-shaped polar capsules unequal in size. The larger polar capsule was 7.6 ± 0.3 (7.1 - 8.4) µm long and 3.5 ± 0.1 (3.3 - 3.8) µm wide, and the smaller polar capsule was 6.2 ± 0.3 (5.5 - 6.7) µm long and 2.9 ± 0.2 (2.6 - 3.4) µm wide. Each polar capsule contained a polar filament with 3-5 coils. A phylogenetic analysis based on the small subunit rDNA (SSU rDNA) sequence revealed that this Myxobolus species forms a distinct branch in the phylogenetic tree sister to Myxobolus artus and Myxobolus cyprini, with DNA sequence similarity at 97.6% to M. artus and 97.5% to M. cyprini. A combination of the morphological characteristics and molecular data suggest that this is an undescribed species, and we propose the name Myxobolus hoabinhensis n. sp.

GENETIC DIVERSITY OF CYSTODISCUS SPECIES IN AMPHIBIANS IN THE SOUTHERN UNITED STATES

Myxosporean species in the genus Cystodiscus are parasites of amphibians and have been reported from several continents. Typically used for the identification of myxozoans, the spores produced by these species are similar to one another, possessing 2 polar capsules and being ovoid. The number of transverse depressions on the spore can be useful for delineating species, but these can sometimes be difficult to distinguish. In North America, Cystodiscus serotinus and Cystodiscus melleni have been described, and for C. serotinus in particular, numerous reports and a wide range of hosts have been associated with this species. Given the challenges of identifying some of these species, we questioned whether all encounters of Cystodiscus species can be attributed to these 2 described species, or if there may be additional undescribed species or cryptic species. Over 7 yr, 383 amphibians representing 13 species of toads, frogs, and salamanders were collected from sites in Oklahoma and Arkansas. Cystodiscus infections were found in 56 individuals (14.6%). Tissues from these infected individuals were preserved in alcohol for genetic analysis. The small subunit (SSU) and large subunit (LSU) ribosomal RNA genes were partially sequenced and analyzed phylogenetically. Nine distinct SSU sequence types and 7 distinct LSU sequence types were identified. Phylogenetically, sequence types were attributable to C. serotinus, C. melleni, Cystodiscus axonis, and an undescribed species. For the previously described species, there were multiple SSU sequence types: 4 for C. serotinus and 2 for both C. melleni and C. axonis. Phylogenetic patterns were similar for the LSU sequence analysis using a shorter sequence than the SSU, and we propose that the LSU is useful for initial barcoding of Cystodiscus species in any future surveys. In our qualitative assessment of sequence types compared to geography and host species, SSU types C1 and C2 (C. axonis) were only found in Union County, Arkansas, and McCurtain County, Oklahoma, respectively. Also, salamanders were only infected with SSU types B or D (C. melleni), and type B was only found in salamanders. Our finding of C. axonis in North America is notable because this species was described in Australia and is associated with host pathology. Our work reveals that there are cryptic species of Cystodiscus in the United States, one of which may be a pathogen, highlighting the importance of genetic analysis for future surveys of these species.

Broad but restricted detection of malacosporeans in a Neotropical cradle of diversification

This study undertook the first investigation of malacosporean infections in Neotropical fish. We used polymerase chain reaction detection with a primer set generally targeting known malacosporeans to assay for infection in the kidney of 146 fish in 21 species belonging to 12 families collected from two areas in the Amazon Basin. Infections were found in 13 fish variously belonging to seven species in six families and included the first identification of a malacosporean infection in cartilaginous fish (a freshwater stingray). Based on ssrDNA, all infections represented a single Buddenbrockia species (Buddenbrockia sp. E) that demonstrates an exceptionally broad range of fish species infected, and countered our expectations of high Neotropical malacosporean diversity. Infections were characterized at varying and often high prevalences in fish species but sample sizes were small. Ascertaining whether highly divergent malacosporeans have not been detected by current primers, and more comprehensive sampling may reveal whether malacosporeans are truly as species poor in the Amazon Basin as present data suggest. Our results prompt speculations about evolutionary scenarios including introduction via marine incursions and patterns of host use over time.

Mechanisms and Drivers for the Establishment of Life Cycle Complexity in Myxozoan Parasites

It is assumed that complex life cycles in cnidarian parasites belonging to the Myxozoa result from incorporation of vertebrates into simple life cycles exploiting aquatic invertebrates. However, nothing is known about the driving forces and implementation of this event, though it fostered massive diversification. We performed a comprehensive search for myxozoans in evolutionary ancient fishes (Chondrichthyes), and more than doubled existing 18S rDNA sequence data, discovering seven independent phylogenetic lineages. We performed cophylogenetic and character mapping methods in the largest monophyletic dataset and demonstrate that host and parasite phylogenies are strongly correlated, and that tectonic changes may explain phylogeographic clustering in recent skates and softnose skates, in the Atlantic. The most basal lineages of myxozoans inhabit the bile of chondrichthyans, an immunologically privileged site and protective niche, easily accessible from the gut via the bile duct. We hypothesize that feed-integration is a likely mechanism of host acquisition, an idea supported by feeding habits of chimaeras and ancient sharks and by multiple entries of different parasite lineages from invertebrates into the new host group. We provide exciting first insights into the early evolutionary history of ancient metazoan parasites in a host group that embodies more evolutionary distinctiveness than most other vertebrates.

Myxobolus sp. (Myxozoa; Myxosporea) causing asymptomatic parasitic gill disease in Astyanax aff. bimaculatus (Characiformes; Characidae) in the Tocantins river basin, amazon region, Brazil

Abstract The middle course of the Tocantins river is located in the eastern portion of the “Legal Amazon” region of Brazil and the Dantas river is one of its tributaries. Among the components of the aquatic biota, eukaryote microparasites establish direct relationships with several species of fish and have zoonotic potential that is still little known. Myxozoans stand out among these parasites: they cause myxosporidiosis, a disease that gives rise to high mortality rates worldwide. The genus Myxobolus accounts for the largest number of species that have been described. Thirty specimens of Astyanax aff. bimaculatus that had been caught in the Dantas river were examined. The prevalence of cysts with spores morphologically compatible with myxozoans of the genus Myxobolus in the arcuate and gill filaments of these specimens was 20%.

Extensive Uncharted Biodiversity: The Parasite Dimension

Parasites are often hidden in their hosts and exhibit patchy spatial distributions. This makes them relatively difficult to detect and sample. Consequently we have poor knowledge of parasite diversities, distributions, and extinction. We evaluate our general understanding of parasite diversity and highlight the enormous bias in research on parasites such as helminths and arthropods that infect vertebrate hosts. We then focus on Myxozoa as an exemplary case for demonstrating uncharted parasite diversity. Myxozoans are a poorly recognized but speciose clade of endoparasitic cnidarians with complex life cycles that have radiated to exploit freshwater, marine, and terrestrial hosts by adopting strategies convergent to those of parasitic protists. Myxozoans are estimated to represent some 20% of described cnidarian species-greatly outnumbering the combined species richness of scyphozoans, cubozoans, and staurozoans. We summarize limited understanding of myxozoan diversification and geographical distributions, and highlight gaps in knowledge and approaches for measuring myxozoan diversity. We close by reviewing methods and problems in estimating parasite extinction and concerns about extinction risks in view of the fundamental roles parasites play in ecosystem dynamics and in driving host evolutionary trajectories.

Morphological, histological and molecular characterization of Myxobolus kingchowensis and Thelohanellus cf. sinensis infecting gibel carp Carassius auratus gibelio (Bloch, 1782)

A Myxobolus species and a Thelohanellus species infecting Carassius auratus gibelio (Bloch, 1782) were redescribed by their morphological, histological and molecular characterization. In the present study, the Myxobolus species infecting the muscle was identified as Myxobolus kingchowensis Chen et Ma, 1998 by the morphological and molecular data. Histologically, mature spores of M. kingchowensis were observed in the intercellular and connective tissue of muscle, though the plasmodia were not found. In addition, scattered spores also occurred in the intercellular of haematopoietic cells, intraepithelial of the renal tubules and interior of the melano-macrophage centres. Phylogenetic analysis showed that M. kingchowensis clustered in the clade of muscle-infecting Myxobolus species, further supporting muscle as the infection site of M. kingchowensis. The present Thelohanellus species infecting the gills was identified conspecific as Thelohanellus sinensis reported in Sun (2006) (mark it as T. sinensis-Sun)based on spore morphology, biological traits (host specificity and organ specificity), and molecular data. However, compared with the original description of T. sinensis Chen et Hsieh, 1960, the present Thelohanellus species and T. sinensis-Sun both infecting the gills of gibel carp are distinguishable from the original description in the host and infection site, which made the validity of T. sinensis-Sun dubious. Due to the absence of molecular data in the original description of T. sinensis, we suggest marking the present species and T. sinensis-Sun as T. cf. sinensis to avoid the confusion until T. sinensis is obtained from the type host and type infection site.

Melanomacrophage functions in the liver of the caecilian Siphonops annulatus

Melanomacrophages are phagocytes that synthesize melanin. They are found in the liver and spleen of ectothermic vertebrates, and in the kidney of fish. In agnathan and elasmobranch fish, melanomacrophages are seen as isolated cells, and forming clusters in all the other vertebrates. The natural phagocytic activity of melanomacrophages is poorly characterized, as most of the research works have focused on induced phagocytic activity only. Furthermore, little is known about amphibian melanomacrophages, mainly about those in caecilians - wormlike amphibians in the order of Gymnophiona, which is the least known group of terrestrial vertebrates. The present research work aimed at the structure and function of hepatic melanomacrophages of Siphonops annulatus, a species largely found in South America. We identified the role of these cells in the control of circulating basophils (pro-melanogenic cells), in the turnover of liver collagen stroma and in the hemocatheresis, interrelated physiological mechanisms.