Trichobilharzia mergi sp. nov. (Trematoda: Digenea: Schistosomatidae), a visceral schistosome of Mergus serrator (L.) (Aves: Anatidae)

Parasitological investigations on red-breasted mergansers (Mergus serrator L.) in Iceland revealed digenean flukes of the family Schistosomatidae. Adult worms were detected in blood vessels of the large intestine and eggs were deposited in the mucosa and surrounded by granulomatous reactions. Traditional morphological methods showed that the flukes have very slender filiform bodies, males are equipped with a short gynaecophoric canal and both suckers and spatulate ends are present on each sex. Among characteristics of the flukes which render them morphologically distinct from other Trichobilharzia species are: i) males—well developed vesicula seminalis (v.s.) consisting of a short v.s. externa and a significantly longer (approx. 3 times) v.s. interna, unusually well developed genital papilla and localization of the first testis a relatively long distance posterior to the gynaecophoric canal; ii) eggs—small and elongated with slightly rounded poles and a short terminal spine. DNA taxonomic techniques confirmed that a new species had been identified, Trichobilharzia mergi sp. n. The sequence data were deposited in GenBank under the accession numbers JX456151 to JX456172. Comparison of the results with our previously published data on characterization of DNA of cercariae isolated from freshwater lymnaeid snails showed that larval development of T. mergi is associated with Radix balthica L. (=Radix peregra Müller, 1774; = Radix ovata Draparnaud, 1805).     

Evolutionary relationships among the Schistosomatidae (Platyhelminthes:Digenea) and an Asian origin for Schistosoma

Schistosome blood flukes parasitize birds, mammals, and crocodilians and are responsible for causing one of the great neglected diseases of humanity, schistosomiasis. A phylogenetic study of 10 schistosome genera using approximately 1,100 bases of the large subunit of the nuclear ribosomal gene complex revealed 2 major clades. One clade is entirely mammalian and includes the genera Schistosoma and Orientobilharzia. A close examination of relationships in this group suggests that the medically important Schistosoma arose in Asia and not in Africa as generally presumed and is paraphyletic. The second clade is primarily avian, consisting of 6 genera of exclusively avian parasites and 2 genera of North American mammal flukes. These results indicate a secondary host capture of mammals on the North American continent. This study provides little evidence concerning the ancestral molluscan or vertebrate schistosome host but does demonstrate that host switching has been an important feature of schistosome evolution. Evidence also indicates that the reduced sexual dimorphism characteristic of some avian schistosomes is derived evolutionarily.     

Schistosoma mansoni, S. japonicum, S. haematobium: glycogen content and glucose uptake in parasites from fasted and control hosts

The glycogen content of male and female Schistosoma mansoni has been measured in flukes from normally fed hosts and those from fasted hosts. In infections from both the mouse and the hamster, a significant reduction in schistosomal glycogen of males is seen hours after food is withdrawn from the host. Reductions in protein content of the schistosomes were only observed in hamster infections fasted at least 72 hr. The livers of infected mice not only decrease in size during fasting, but there is a concomitant reduction in glycogen per unit wet weight. Comparisons of glycogen:protein ratios of mansonian males, females, and host livers indicate that the fasting-induced loss of liver glycogen is also observed in the male schistosome, but not the female. Studies of both S. mansoni and S. haematobium pairs from fed hosts suggest that the ratio of glycogen:protein contents in the male schistosome correlates with the glycogen:protein ratio of the female partner. Measurements of glucose uptake in vitro suggest that greater uptake rates may be observed in flukes perfused from fasted hosts. In S. japonicum from infected mice, a reduction in male glycogen was also detected as early as after a 6-hr fasting period, but changes in the females were not significant. Unmated male S. japonicum also exhibit a reduction in glycogen levels after fasting, but the quantity of worm glycogen present in these males remains higher than comparable mated males. In mice entrained to a regulated pattern of available food, fluctuations in glycogen content of the male schistosomes were observed, but in the female partners fluctuations were of a smaller magnitude.(ABSTRACT TRUNCATED AT 250 WORDS)     

The complete mitochondrial genome of the bird schistosome Trichobilharzia regenti (Platyhelminthes: Digenea), causative agent of cercarial dermatitis

The complete mitochondrial (mt) genome of the neuropathogenic bird schistosome Trichobilharzia regenti was fully sequenced in order to develop molecular markers for future diagnostic, molecular ecological, population, and phylogenetic studies. The genome was 14,838 bp in length, with a 68.4% AT bias in protein coding regions. A repeat element (3 x 184 bp) between trnV and trnW distinguished a single short noncoding region. As 9 of 14 genera of schistosomes parasitize birds, future characterization of their mt genomes is desirable for species-specific and strain- or population-specific diagnostic markers; this concerns not only the nasal representatives, e.g., T. regenti characterized in this study, but also numerous species within the predominant group of visceral (blood dwelling) bird schistosomes.     

Polymorphism of the <Emphasis Type="Italic">cox1</Emphasis> gene in cercariae isolates of bird schistosomes (Trematoda:Schistosomatidae) from ponds of Moscow and Moscow region

Polymorphism of a 810-bp fragment of mitochondrial cox1 gene was studied in 15 cercariae isolates of bird schistosomes (family Schistosomatidae), which were collected in water bodies of Moscow and Moscow oblast and represented three species: Trichobilharzia szidati, T. franki, and T. regenti. A substantial predominance of AT (65.4%) was characteristic of the cox1 sequences in all three species. Rare single nucleotide substitutions determined low (0.2–0.9%) intraspecific nucleotide and amino acid sequence diversity. Haplotype diversity h was high (80–100%) in all three species, suggesting a unique character for almost all cox1 sequences in the sample. Phylogenetic trees based on the nucleotide and amino acid sequence variations were constructed to study the relationships of the three schistosome species. A high support was observed for the main branching node that reflects differentiation of the monophyletic group Trichobilharzia and species of the genera Bilharziella (B. polonica), Dendritobilharzia (D. pulverulenta), and Gigantobilharzia (G. huronensis). Based on the nucleotide substitutions and amino acid polymorphisms, two groups of isolates, which parasitize Lymnaea stagnalis (T. szidati) and snails of the group Radix (T. franki and T. regenti) respectively, were isolated in the genus Trichobilharzia. The time of divergence between the two schistosome groups infecting snails of the genera Radix and Lymnaea was calculated from the cox1 nucleotide substitution rate, which is known for Asian and Indian blood flukes from the genus Schistosoma and is 2–3% per million years on average. Divergence of the three bird schistosome species under study and divergence of the Asian species of mammalian schistosomes were almost concurrent, dating back to 2.5–3.8 Myr ago. Factors responsible for the lack of intraspecific subdivision with respect to the cox1 in bird schistosomes and the lack of separation between two species (T. franki and T. regenti) are discussed.     

Two avian schistosome cercariae from Nepal,including a Macrobilharzia-like species from Indoplanorbis exustus

As part of a global survey of schistosomes, a total of 16,109 freshwater snails representing 14 species were collected from lakes, ponds, rivers, rice fields and swamps mostly in the Terai region of southern Nepal. Only two snails were found to harbor avian schistosome cercariae even though Nepal is well known for its rich avian diversity. One schistosome infection was from an individual of Radix luteola and on the basis of phylogenetic analyses using 28S rDNA and cox1 sequences, grouped as a distinctive and previously unknown lineage within Trichobilharzia. This genus is the most speciose within the family Schistosomatidae. It includes 40 described species worldwide, and its members mostly infect anseriform birds (ducks) and two families of freshwater snails (Lymnaeidae and Physidae). The second schistosome cercaria was recovered from an individual of Indoplanorbis exustus that was also actively emerging a Petasiger-like echinostome cercaria. Although I. exustus is commonly infected with mammalian schistosomes of the Schistosoma indicum species group on the Indian subcontinent, this is the first specifically documented avian schistosome reported in this snail. Both cercariae reported here are among the largest of all schistosome cercariae recovered to date. The I. exustus-derived schistosome clustered most closely with Macrobilharzia macrobilharzia, although it seems to represent a distinct lineage. Specimens of Macrobilharzia have thus far not been recovered from snails, being known only as adult worms from anhingas and cormorants. This study is the first to characterize by sequence data avian schistosomes recovered from Asian freshwater habitats. This approach can help unravel the complex of cryptic species causing cercarial dermatitis here and elsewhere in the world.     

The morphology and life-cycle of Trichobilharzia arcuata n. sp. (Schistosomatidae: Bilharziellinae) a nasal schistosome of water whistle ducks (Dendrocygna arcuata) in Australia

Summary The morphology and life-cycle of Trichobilharzia arcuata n. sp. from the nasal blood vessels of Dendrocygna arcuata from northern Australia are described. T. arcuata is distinguished from all species of Trichobilharzia except T. australis and African nasal schistosomes by its location in the nasal blood vessels and by the cercariae having 16 flame cells with a formula 2[(3)+(4+1)] against 14 with a formula 2[(3)+(3+1)], or 12 with a formula 2[(3)+(2+1)] in the case of T. corvi. T. arcuata differs from the five African nasal schistosomes in the nature of the tegument, the position of the male genital papilla and the shape of the eggs and from T. australis in the position of the caecal reunion, the number of testes, the absence of spines on the ventral tegument between the ovary and the seminal receptacle, the shape of the eggs and the presence of two germinal masses in the miracidium. Lymnaea lessoni exposed to miracidia of T. arcuata developed patent infection in 22 to 41 days. Intramolluscan development of T. arcuata is similar to T. stagnicolae and T. physellae. Domestic Muscovy ducks and pigeons developed patent infections in 22 and 12 days respectively. Chickens, a black duck and a grey teal did not become infected. ac]19840616     

Molecular taxonomic identification of Schistosomatidae from Naroch Lake and Polonevichi Lake in Belarus

In Belarus, Naroch Lake is the only area with a high incidence of the human cercarial dermatitis (HCD). However, very little is known about the taxonomy of avian schistosomes, the causative agents of the disease, which are found in Naroch Lake and other lakes in Belarus. In this study, we used a molecular approach to investigate the systematic position and biodiversity of avian schistosomes from Naroch Lake and Polonevichi Lake. Based on the sequence analysis of the ITS genomic region, we were able to detect four different species of bird schistosomes in Naroch Lake (Trichobilharzia szidati, Trichobilharzia franki, Bilharziella polonica and a novel Trichobilharzia species) and two species in Polonevichi Lake (T. szidati and B. polonica). The data were used to reveal the phylogenetic position of HCD causative cercariae found in Belarusian water reservoirs and to establish their relationships within the group of avian schistosomes. We discuss the possibility of identifying species of Trichobilharzia using the fragment length polymorphism analysis of the ITS region. Possible epidemiological causes of HCD incidence in Belarus are also discussed.     

Changes in tegumental surface during development of Schistosoma mansoni

The tegumental surface of immature Schistosoma mansoni was studied with the scanning electron microscope. The surfaces of immature males and females bear no resemblance to that of adult worms and are characterized by having many tegumental folds. The tegumental surfaces of immature males and females are similar, and the dorsal and ventral surfaces of the male are similar before formation of the gynecophoral canal. Transition of the tegumental surface from the juvenile to the adult form begins after worms are in copula and have grown to several millimeters in length.     

A newly-identified lineage of Schistosoma

Because of their role in causing schistosomiasis, flukes of the genus Schistosoma are the best known of all digeneans. The genus has traditionally been divided into four familiar species groups. Here we report on three poorly known species of Schistosoma, one of which, Schistosoma hippopotami, is known from the hippopotamus, one of which is provisionally identified as Schistosoma edwardiense, another hippo parasite, and a third that has not previously been described. All were collected from freshwater snails obtained from Lake Edward, western Uganda, the type locality for both known hippo schistosomes. The three different kinds of schistosome cercariae differ from one another in size, and all are readily differentiated by their long tail stems from the cercariae of human-infecting species. Furthermore, each was recovered from a different genus of snail host, Biomphalaria sudanica, Bulinus truncatus or Ceratophallus natalensis. Molecular analysis, based on 8350 bases of combined nuclear and mitochondrial DNA, groups these three long tail-stem cercariae into a well supported clade that does not associate with any of the recognised species groups. The placement of this clade, basal to all African species plus several Asian species, suggests that there has been an ancient association between Schistosoma and hippos. This new African Schistosoma clade advocates the need for further modification of the traditional species group-based classification. Two of the four species groups are paraphyletic. It also suggests that Schistosoma has been remarkably plastic with respect to adapting to snail hosts-three distantly related genera of planorbid snails have been exploited by worms within a single clade. Finally, it adds a new layer of complexity to deciphering the origins of Schistosoma, often considered to be African but recently challenged as being Asian. In the late Cenozoic the distribution of hippo species straddled both Africa and Asia and they may have provided a means for the introduction of blood flukes to Africa.     

Evaluation of Schistosome Promoter Expression for Transgenesis and Genetic Analysis

Schistosome worms of the genus Schistosoma are the causative agents of schistosomiasis, a devastating parasitic disease affecting more than 240 million people worldwide. Schistosomes have complex life cycles, and have been challenging to manipulate genetically due to the dearth of molecular tools. Although the use of gene overexpression, gene knockouts or knockdowns are straight-forward genetic tools applied in many model systems, gene misexpression and genetic manipulation of schistosome genes in vivo has been exceptionally challenging, and plasmid based transfection inducing gene expression is limited. We recently reported the use of polyethyleneimine (PEI) as a simple and effective method for schistosome transfection and gene expression. Here, we use PEI-mediated schistosome plasmid transgenesis to define and compare gene expression profiles from endogenous and nonendogenous promoters in the schistosomula stage of schistosomes that are potentially useful to misexpress (underexpress or overexpress) gene product levels. In addition, we overexpress schistosome genes in vivo using a strong promoter and show plasmid-based misregulation of genes in schistosomes, producing a clear and distinct phenotype- death. These data focus on the schistosomula stage, but they foreshadow strong potential for genetic characterization of schistosome molecular pathways, and potential for use in overexpression screens and drug resistance studies in schistosomes using plasmid-based gene expression.     

Penetration of Trichobilharzia cercariae into mammals: dangerous or negligible event?

Bird schistosomes and cases of human cercarial dermatitis occur worldwide, but the number of cases is not monitored. Experiments with two schistosomes, namely Trichobilharzia szidati and T. regenti, show that they possess potent tools to penetration bird and mammalian skin, as well as exhibit species-specific migration patterns within vertebrate bodies. Therefore, the infections may affect different organs/tissues e.g. lungs or spinal cord. In this minireview, the adaptations and pathogenic effects of bird schistosomes in experimental mammals are discussed, and some ideas/hypotheses on risks to humans from exposure to bird schistosome cercariae are expressed.     

Survival of bird schistosomes in mammalian lungs

Bird schistosome cercariae have a low specificity to vertebrate skin and, thus, they are also able to penetrate into mammals. As a consequence, a hypersensitive skin response-cercarial dermatitis-develops. It was thought that the parasites die in the skin soon after penetration. Our results on Trichobilharzia szidati and Bilharziella polonica in the non-specific murine host confirm that some of the penetrating bird schistosomes may fully transform to schistosomula and migrate to the lungs. They persist there for up to 10days post exposure. In a duck, the worms grow and feed rapidly, but in a mouse the lung schistosomula seem to be inhibited in their development. However, TEM results show that there is no damage to the tegument of these larvae and no immune effector cells attack the parasites. These results suggest that the parasite's failure in the murine host might be caused by some immunologically unrelated factors.     

日本血吸虫中国大陆株抱雌沟蛋白编码基因的克隆和表达

根据曼氏血吸虫抱雌沟蛋白SmGcp序列和日本血吸虫编码抱雌沟蛋白保守区的基因片段jGcp1分别设计三对引物,以日本血吸虫中国大陆株成虫mRNA为模板 ,用RT－PCR法扩增出大小为1949bp的基因片段。经序列分析推断该基因片段含编码日本血吸虫抱雌沟蛋白基因的阅读框,与SmGcp碱基一致性为85％,其理论推测氨基酸组成与曼氏血吸虫抱雌沟蛋白的一致性为83．7％。将上述扩增的基因片段克隆到表达载体pET28c( )中,在大肠杆菌BL21中获得表达,融合表达产物分子量约为80kD。利用日本血吸虫成虫抗原免疫血清对该表达产物进行Western印迹检测,在预测位置出现了明显的识别条带,说明该编码日本血吸虫中国大陆株抱雌沟蛋白基因的表达产物具有抗原性。     

Homosexual male pairing in Schistosoma mansoni

and 1988. Homosexual male pairing in Schistosoma mansoni.International Journal for Parasitology 18: 1115–1117. To see whether male worms within the gynecophoral canal of another male worm would become feminized (i.e. express vestigial female-associated genes), we established homosexual pairs by twice exposing mice to male cercariae with a 4 or 6-week interval, and perfusing 3–5 weeks later. From 13 to 34% of these worms were found in pairs, compared with 0 to 7% in singly exposed controls. ‘Inner’ males in homosexual pairs showed no histological evidence of female reproductive structures, but were stunted, had poorly developed testes, and the high nuclear density characteristic of mature females. More vitelline follicles occurred in unpaired unisexual males than in homosexually paired males, fewest in bisexually paired males. Uptake of tyrosine, an indicator of vitelline development, occurred in the same relative order. The gynecophoral microenvironment often led to stunting, probably through starvation induced by the relative inaccessibility of host blood to homosexually clasped males.     

Schistosoma mansoni: TGF-beta signaling pathways

Schistosome parasites have co-evolved an intricate relationship with their human and snail hosts as well as a novel interplay between the adult male and female parasites. We review the role of the TGF-beta signaling pathway in parasite development, host-parasite interactions and male-female interactions. The data to date support multiple roles for the TGF-beta signaling pathway throughout schistosome development, in particular, in the tegument which is at the interface with the host and between the male and female schistosome, development of vitelline cells in female worms whose genes and development are regulated by a stimulus from the male schistosome and embryogenesis of the egg. The human ligand TGF-beta1 has been demonstrated to regulate the expression of a schistosome target gene that encodes a gynecophoric canal protein in the schistosome worm itself. Studies on signaling in schistosomes opens a new era for investigation of host-parasite and male-female interactions.     

Unusual finding of Trichobilharzia sp. in Motacilla alba in the Czech Republic

Adult male worms of Trichobilharzia sp. recovered from a pied wagtail (Motacilla alba) in the Czech Republic were found to belong to a new species of the genus. The finding of Trichobilharzia sp. in a passeriform bird in Europe represents an important discovery, as only anseriform birds have thus far been reported as final hosts of the European Trichobilharzia species.     

Homosexual male pairing in Schistosoma mansoni

Basch P. F. and Gupta B. C. 1988. Homosexual male pairing in Schistosoma mansoni.International Journal for Parasitology18: 1115–1117. To see whether male worms within the gynecophoral canal of another male worm would become feminized (i.e. express vestigial female-associated genes), we established homosexual pairs by twice exposing mice to male cercariae with a 4 or 6-week interval, and perfusing 3–5 weeks later. From 13 to 34% of these worms were found in pairs, compared with 0 to 7% in singly exposed controls. ‘Inner’ males in homosexual pairs showed no histological evidence of female reproductive structures, but were stunted, had poorly developed testes, and the high nuclear density characteristic of mature females. More vitelline follicles occurred in unpaired unisexual males than in homosexually paired males, fewest in bisexually paired males. Uptake of tyrosine, an indicator of vitelline development, occurred in the same relative order. The gynecophoral microenvironment often led to stunting, probably through starvation induced by the relative inaccessibility of host blood to homosexually clasped males.     

Human U6 promoter drives stronger shRNA activity than its schistosome orthologue in Schistosoma mansoni and human fibrosarcoma cells

Blood flukes or schistosomes are the causative agents of human schistosomiasis, one of the major neglected tropical diseases. Draft genome sequences have been reported for schistosomes, but functional genomics tools are needed to investigate the role and essentiality of the newly reported genes. Vector based RNA interference can contribute to functional genomics analysis for schistosomes. Using mRNA encoding reporter firefly luciferase as a model target, we compared the performance of a schistosome and a human promoter from the U6 gene in driving shRNA in human fibrosarcoma cells and in cultured schistosomes. Further, both a retroviral [Murine leukemia virus (MLV)] and plasmid (piggyBac, pXL-Bac II) vector were utilized. The schistosome U6 gene promoter was 270 bp in length, the human U6 gene promoter was 264 bp; they shared 41% identity. Following transduction of both HT1080 fibrosarcoma cells and schistosomules of Schistosoma mansoni with pseudotyped MLV virions, stronger knockdown of luciferase activity was seen with the virions encoding the human U6 promoter driven shRNA than the schistosome U6 promoter. A similar trend was seen after transfection of HT1080 cells and schistosomules with the pXL-Bac-II constructs-stronger knockdown of luciferase activity was seen with constructs encoding the human compared to schistosome U6 promoter. The findings indicate that a human U6 gene promoter drives stronger shRNA activity than its schistosome orthologue, not only in a human cancer cell line but also in larval schistosomes. This RNA polymerase III promoter represents a potentially valuable component for vector based RNA interference studies in schistosomes and related platyhelminth parasites.