Evidence of a Putative Novel Species of Avian Schistosome Infecting Planorbella trivolvis.

Freshwater gastropods of the genera Lymnaea Lamarck, 1799, Physa Draparnaud, 1801, Gyraulus Charpentier, 1837, Radix Montfort, 1810, and Stagnicola Jeffreys, 1830 are considered suitable intermediate hosts for avian schistosomes. A large trematode biodiversity survey performed across 3 yr on 6 lakes in Alberta confirmed 3 already-reported snail hosts for 7 North American avian schistosomes; however, the cytochrome c oxidase subunit 1 (COI) nucleotide sequence from 1 cercarial sample (from a single specimen of Planorbella trivolvis) was distinct from all other COI schistosome sequences. As part of a simultaneous, comparable study of P. trivolvis by us in Michigan, we collected another cercarial type from 6 lakes that was 99% similar (COI) to the aforementioned cercarial type. Phylogenetic analyses of the COI and 28S rDNA genes recovered the former cercaria in a clade of avian schistosomes. In Michigan, the feces of a Canada goose (Branta canadensis Linnaeus, 1758) had a miracidium with an identical COI nucleotide sequence. Preliminary swimmer's itch and cercarial emergence studies were performed to determine if the cercariae could cause swimmer's itch and to study the emergence pattern as compared with species of Trichobilharzia Skrjabin and Zakharow, 1920.

Migratory routes, domesticated birds and cercarial dermatitis: the distribution of Trichobilharzia franki in Northern Iran.

BACKGROUND: One of the major migration routes for birds going between Europe and Asia is the Black Sea-Mediterranean route that converges on the Volga Delta, continuing into the area of the Caspian Sea. Cercarial dermatitis is a disorder in humans caused by schistosome trematodes that use aquatic birds and snails as hosts and is prevalent in areas of aquaculture in Northern Iran. Before the disorder can be addressed, it is necessary to determine the etiological agents and their host species. This study aimed to document whether domestic mallards are reservoir hosts and if so, to characterize the species of schistosomes. Previous work has shown that domestic mallards are reservoir hosts for a nasal schistosome. RESULTS: In 32 of 45 domestic mallards (Anas platyrhynchos domesticus) (71.1%), the schistosome Trichobilharzia franki, previously reported only from Europe, was found in visceral veins. Morphological and molecular phylogenetic analysis confirmed the species designation. These findings extend the range of T. franki from Europe to Eurasia. CONCLUSION: The occurrence of cercarial dermatitis in Iran is high in areas of aquaculture. Previous studies in the area have shown that domestic mallards are reservoir hosts of T. regenti, a nasal schistosome and T. franki, as shown in this study. The genetic results support the conclusion that populations of T. franki from Iran are not differentiated from populations in Europe. Therefore, the schistosomes are distributed with their migratory duck hosts, maintaining the gene flow across populations with compatible snail hosts in Iran.

TITLE: Routes migratoires, oiseaux domestiques et dermatite cercarienne : répartition de Trichobilharzia franki dans le nord de l'Iran. ABSTRACT: Contexte : L'une des principales voies de migration des oiseaux à destination et en provenance de l'Europe et de l'Asie est la route mer Noire-Méditerranée qui converge vers le delta de la Volga et se poursuit dans la région de la mer Caspienne. La dermatite cercarienne est une affection causée chez l'homme par des trématodes Schistosomatidae utilisant des oiseaux aquatiques et des mollusques comme hôtes, qui est répandue dans les zones d'aquaculture du nord de l'Iran. Avant de pouvoir lutter contre cette parasitose, il est nécessaire de connaître les agents étiologiques et leurs espèces hôtes. Ce travail vise à documenter si les canards domestiques sont des hôtes réservoirs et si oui, à caractériser les espèces de schistosomes. Des travaux antérieurs ont montré que les canards domestiques sont des hôtes réservoirs pour un schistosome nasal. Résultats : Chez 32 de 45 canards domestiques (Anas platyrhynchos domesticus) (71,1 %), le schistosome Trichobilharzia franki, précédemment signalé uniquement en Europe, a été trouvé dans les veines viscérales. L'identification de l'espèce a été vérifiée par une analyse morphologique et phylogénétique moléculaire. Cela étend l'aire de répartition de l'Europe à l'Eurasie. Conclusion : La dermatite cercarienne est répandue dans les zones d'aquaculture en Iran. Des travaux antérieurs dans la région ont montré que les canards domestiques sont des hôtes réservoirs de T. regenti, un schistosome nasal et de T. franki, comme le montre cette étude. Les résultats génétiques soutiennent que les populations de T. franki d'Iran ne sont pas différenciées des populations d'Europe. Par conséquent, les schistosomes se dispersent avec leur hôte canard lors de la migration, maintenant un flux génétique entre les populations avec des mollusques hôtes compatibles en Iran.

Morphological and genomic characterisation of the Schistosoma hybrid infecting humans in Europe reveals admixture between Schistosoma haematobium and Schistosoma bovis.

Schistosomes cause schistosomiasis, the world's second most important parasitic disease after malaria in terms of public health and social-economic impacts. A peculiar feature of these dioecious parasites is their ability to produce viable and fertile hybrid offspring. Originally only present in the tropics, schistosomiasis is now also endemic in southern Europe. Based on the analysis of two genetic markers the European schistosomes had previously been identified as hybrids between the livestock- and the human-infective species Schistosoma bovis and Schistosoma haematobium, respectively. Here, using PacBio long-read sequencing technology we performed genome assembly improvement and annotation of S. bovis, one of the parental species for which no satisfactory genome assembly was available. We then describe the whole genome introgression levels of the hybrid schistosomes, their morphometric parameters (eggs and adult worms) and their compatibility with two European snail strains used as vectors (Bulinus truncatus and Planorbarius metidjensis). Schistosome-snail compatibility is a key parameter for the parasites life cycle progression, and thus the capability of the parasite to establish in a given area. Our results show that this Schistosoma hybrid is strongly introgressed genetically, composed of 77% S. haematobium and 23% S. bovis origin. This genomic admixture suggests an ancient hybridization event and subsequent backcrosses with the human-specific species, S. haematobium, before its introduction in Corsica. We also show that egg morphology (commonly used as a species diagnostic) does not allow for accurate hybrid identification while genetic tests do.

Imaging schistosomes in vivo.

Schistosomes are intravascular, parasitic helminths that cause a chronic, often debilitating disease afflicting over 200 million people in over 70 countries. Here we describe novel imaging methods that, for the first time, permit visualization of live schistosomes within their living hosts. The technology centers on fluorescent agent uptake and activation in the parasite's gut, and subsequent detection and signal quantitation using fluorescence molecular tomography (FMT). There is a strong positive correlation between the signal detected and parasite number. Schistosoma mansoni parasites of both sexes recovered from infected experimental animals exhibit vivid fluorescence throughout their intestines. Likewise, the remaining important human schistosome parasites, S. japonicum and S. hematobium, also exhibit gut fluorescence when recovered from infected animals. Imaging has been used to efficiently document the decline in parasite numbers in infected mice treated with the antischistosome drug praziquantel. This technology will provide a unique opportunity both to help rapidly identify much-needed, novel antischistosome therapies and to gain direct visual insight into the intravascular lives of the major schistosome parasites of humans.

Schistosoma kisumuensis n. sp. (Digenea: Schistosomatidae) from murid rodents in the Lake Victoria Basin, Kenya and its phylogenetic position within the S. haematobium species group.

Schistosoma kisumuensis n. sp. is described based on 6 adult males and 2 adult females collected from the circulatory system of 3 murid rodent species, Pelomys isseli, Mastomys natalensis, and Dasymys incomtus. Specimens were collected from a single location, Nyabera Swamp, in Kisumu, Kenya in the Lake Victoria Basin. This new species is morphologically similar to members of the S. haematobium group, currently represented by 8 species parasitizing artiodactyls and primates, including humans. Schistosoma kisumuensis differs from these species by producing relatively small Schistosoma intercalatum-like eggs (135.2 x 52.9 microm) with a relatively small length to width ratio (2.55). Comparison of approximately 3000-base-pair sequences of nuclear rDNA (partial 28S) and mtDNA (partial cox1, nad6, 12S) strongly supports the status of S. kisumuensis as a new species and as a sister species of S. intercalatum. The cox1 genetic distance between these two species (6.3%) is comparable to other pairwise comparisons within the S. haematobium group. Separation of the Congo River and Lake Victoria drainage basins is discussed as a possible factor favoring the origin of this species.

Schistosomes in the southwest United States and their potential for causing cercarial dermatitis or 'swimmer's itch'.

Cercarial dermatitis or swimmer's itch results when cercariae of schistosomes penetrate human skin and initiate inflammatory responses. The parasites typically die in the skin but in some cases may persist and infect other organs. Cercarial dermatitis is caused by a complex and poorly known assemblage of schistosome species, and can occur in any location where people come in contact with water bodies harbouring schistosome-infected snails. In North America, most cases are reported from the upper Midwest. In south-western USA, this phenomenon has not been well studied, and it is not known which schistosome species are present, or if cercarial dermatitis occurs with any regularity. As part of our ongoing studies of schistosome diversity, using morphological traits and sequence data to differentiate species, we have thus far identified eight schistosome genetic lineages from snails from New Mexico and Colorado. We have investigated two cercarial dermatitis outbreaks, one occurring in Stubblefield Lake in northern New Mexico, and one in Prospect Lake in the heart of Colorado Springs, Colorado. The New Mexico outbreak involved either one or two different avian schistosome species, both transmitted by physid snails. The Colorado outbreak was due to Trichobilharzia brantae, a species transmitted by geese and the snail Gyraulus parvus. These outbreaks are in contrast to those in northern states where schistosomes infecting snails of the family Lymnaeidae are more often responsible for outbreaks. Our survey suggests that dermatitis-causing schistosomes are not rare in the southwest, and that there are plenty of opportunities for dermatitis outbreaks to occur in this region.

[The structure and function of schistosome tegument and related proteomic study].

Schistosome is covered by a living syncytium, called tegument, which plays important role in nutrient uptake and immune evasion. Recently, tegumental proteomic research identified lots of proteins, of which there may be potential targets for diagnosis, drugs and vaccines.

Allobilharzia visceralis gen. nov., sp. nov. (Schistosomatidae-Trematoda) from Cygnus cygnus (L.) (Anatidae).

In Iceland, the examination of whooper swans (Cygnus cygnus L.) viscera resulted in the detection of adult digenean flukes of the family Schistosomatidae. The mature worms occurring in the blood vessels of the large intestine and mesenterium caused vascular lesions, around the eggs deposited in the intestinal mucosa and liver granulomatous reactions developed. The morphology of the isolated schistosomes shows certain similarity with the flukes of the genus Trichobilharzia; in males reduced gynecophoral canal, and on both sexes both suckers and spatulate ends are present. However, the Icelandic flukes possess other morphological features which are distinct from the genus: the point of caecal reunion in males takes place posterior to gynecophoral canal and the genital pore is behind acetabulum and anterior to caecal reunion. In order to evaluate the identity of Icelandic schistosomes, sequencing of ITS region of DNA was performed, and the obtained sequence was deposited in GenBank under the accession no. DQ067561. Following phylogenetic analysis of relationship between the sequence of Icelandic flukes and database sequences of other bird schistosome genera (Trichobilharzia, Gigantobilharzia and Dendritobilharzia) showed different position of Icelandic worms in the phylogenetic tree. In conclusion, our study revealed new genus and species of schistosome flukes--Allobilharzia visceralis gen. et sp. n.

Seasonal morphological variations in bird schistosomes.

The present work is a contribution to the systematics of Bilhorziello and Dendritobilharzio. Wildfowl was killed in hunting seasons or found dead in Champagne-Ardenne region, France, and autopsied with focus on schistosomes. Seven Anas plotyrhynchos (mallards), one Ardeo cinerea (grey heron) and two Cygnus olor (mute swans) were parasitized by Bilharziella. One C. olor was parasitized by Dendritobilharzia. Depending on season and hosts, various morphological forms of Bilharziello suggesting several species were observed. The differences in male and female worms concerned the morphology of genital apparatus, the spination on suckers, the body size and proportions. However, the comparison of DNA sequences led to a conclusion that these forms belonged to one species, Bilharziella polonica (Kowalewski, 1895). The morphological features and the body sizes of our samples of Dendritobilharzia seemed to differ from the type species of D. pulverulenta (Braun, 1901). Nevertheless, molecular analysis confirmed identity. We hypothesize that the differences in Bilharziella and Dendritobilharzia might be linked to internal host factors (e.g. hormonal levels), and influenced by season, host, and worm age. The definition of the genera Bilharziello and Dendritobilharzio was amended.

The Tao survivorship of schistosomes: implications for schistosomiasis control.

Schistosomiasis, caused by blood flukes of the genus Schistosoma, is a major public health problem which contributes substantially to the economic and financial burdens of many nations in the developing world. An array of survival strategies, such as the unique structure of the tegument which acts as a major host-parasite interface, immune modulation mechanisms, gene regulation, and apoptosis and self-renewal have been adopted by schistosome parasites over the course of long-term evolution with their mammalian definitive hosts. Recent generation of complete schistosome genomes together with numerous biological, immunological, high-throughput "-omics" and gene function studies have revealed the Tao or strategies that schistosomes employ not only to promote long-term survival, but also to ensure effective life cycle transmission. New scenarios for the future control of this important neglected tropical disease will present themselves as our understanding of these Tao increases.

Structure-function analysis of apical membrane-associated molecules of the tegument of schistosome parasites of humans: prospects for identification of novel targets for parasite control.

Neglected tropical diseases are a group of some 17 diseases that afflict poor and predominantly rural people in developing nations. One significant disease that contributes to substantial morbidity in endemic areas is schistosomiasis, caused by infection with one of five species of blood fluke belonging to the trematode genus Schistosoma. Although there is one drug available for treatment of affected individuals in clinics, or for mass administration in endemic regions, there is a need for new therapies. A prominent target organ of schistosomes, either for drug or vaccine development, is the peculiar epithelial syncytium that forms the body wall (tegument) of this parasite. This dynamic layer is maintained and organized by concerted activity of a range of proteins, among which are the abundant tegumentary annexins. In this review, we will outline advances in structure-function analyses of these annexins, as a means to understanding tegument cell biology in host-parasite interaction and their potential exploitation as targets for anti-schistosomiasis therapies.

Schistosomiasis in the Mekong region: epidemiology and phylogeography.

An account is given of progress made over the last 20 years in the study of Mekong schistosomiasis, causative agent Schistosoma mekongi (Trematoda: Digenea). Emphasis is given to the discussion of work concerning the origin and subsequent dispersal of S. mekongi and related taxa, including relevant snails. The role of such phylogeographical data in schistosomiasis control and the prediction of areas at risk is examined. New palaeogeographical models are reviewed in relation to traditional explanations for the biogeographic deployment of Southeast Asian Schistosoma and their intermediate hosts. The demographics and molecular ecology of Neotricula aperta (Gastropoda: Pomatiopsidae), the snail host of S. mekongi, are reviewed with particular reference to new models for the life cycle of this species and their importance in snail control. The use of population genetic data in the limitation of N. aperta populations is evaluated and strategies suggested for schistosomiasis control efforts directed against the intermediate host. Developments in the taxonomy of N. aperta, and related taxa, and changes in nomenclature are covered. The direction of future investigations into the problem of Mekong schistosomiasis is also discussed.

Nutritional adaptations to parasitism within the platyhelminthes.

Some of the most significant alterations to the basic turbellarian plan are evident in the adaptations that relate to the acquisition of food by parasitic flatworms, reflecting the most potent of selection pressures in initiating and maintaining the host-parasite association. Nutritionally, ectoparasitic monogeneans show most correspondence with the predatory turbellarians, with certain monopisthocotylean members feeding by means of a protrusible pharynx and extracorporeal digestion, as skin-browsers of fish, with extensive intracellular digestion involving lysosomal enzymes in a well-differentiated gut. The more sheltered vascularised gill chamber of fish provides many polyopisthocotylean monogeneans with a totally renewable and more comprehensive diet in the form of blood, but haematophagy has necessitated a number of digestive adaptations, not least in resolving the problem of intracellular accumulations of haematin pigment. Haematophagy is the predominant feeding strategy of digeneans, but in contrast to monogeneans digestion of blood is largely extracellular; in schistosomes digestion is rapid, involving a battery of cathepsin-like cysteine proteinases and aminopeptidases. The external surfaces of all parasitic flatworms depart from turbellarian character and are composed of a multifunctional syncytial tegument, which is permeable to a variety of small organic solutes, some crossing by passive diffusion, others via facilitated or active mediated transport. The relative roles of the tegument and gut in trematode nutrition are difficult to assess, but can be related to the nature of the microhabitat within the host. Cestodes are highly adapted intestinal parasites bereft of any vestige of gut, and their tegument has become elaborated into a sophisticated and highly efficient digestive-absorptive layer, rivalling the vertebrate mucosa in its ability to gain kinetic advantage in the selective uptake of nutrient at the host-parasite interface. The patterns of energy metabolism in adult flatworm parasites are generally anaerobic and based on glycogen, with abbreviated metabolic pathways and the loss of biosynthetic capacities.

A new focus of Schistosoma haematobium/S. intercalatum hybrid in Cameroon.

Terminal-spined schistosome eggs were found in both stool and urine specimens of a high proportion of infected individuals in Kinding Njabi, a village located in a savannah/forest ecotone of Center Province, Cameroon. Infections with terminal-spined schistosomes are not common in that region and first appeared in Kinding Njabi in the mid-1980s. The village population, determined by house-to-house census in 1986, was 345. Of 302 stool samples examined by a thick smear technique, 58 (19%) were positive, and of 320 urine samples examined by sedimentation, 40 (12%) were positive. Twenty-six (37%) of a total of 71 infected persons passed eggs in both stool and urine. Egg size distribution and morphology were similar to previous reports for Schistosoma haematobium/S. intercalatum hybrids. Bulinus forskalii was the only snail found during extensive surveys in and around Kinding Njabi; infected snails were recovered from several temporary habitats. This focus is of particular interest because it represents the first report of transmission of hybrid schistosomes outside of the hybrid zone. Interviews with villagers and local health officials suggest that schistosomiasis was introduced by immigrants from Loum, a town approximately 100 km southwest of Kinding Njabi, where S. haematobium, S. intercalatum, and their hybrid are known to exist. Results from snail host specificity studies using the Kinding Njabi parasite showed that stool-derived miracidia were compatible only with B. forskalii, the exclusive host for S. intercalatum in Cameroon. Urine-derived miracidia were compatible only with B. truncatus, a S. haematobium host in Cameroon.(ABSTRACT TRUNCATED AT 250 WORDS)

Argentophilic papillae of Schistosomatium douthitti cercariae (Trematoda: Schistosomatidae).

Argentophilic papillae of cercariae of Schistosomatium douthitti were studied by light microscopy. The basic number of body papillae was 56, excluding 20 at the anterior tip. The average number of tail papillae was 18. Average locations and spatial ranges of body papillae indicate a rather constant pattern. Tail papillae showed greater variability in location. Twenty papillae (10 on each side) at the anterior tip of cercariae were associated with gland duct openings. Two types of papillae were recognized with light microscopy--uniciliated bulbs and pits. The papilla pattern of S. douthitti differs from those of other species of schistosomes derived to date, and its constancy supports the usefulness of papillae in systematic studies.

Patterns of argentophilic papillae of Schistosoma rodhaini and S. mansoni cercariae.

Argentophilic papillar patterns on cercariae of Schistosoma rodhaini from Kenya and S. Africa, and S. mansoni from Kenya and Brazil were compared with each other and with earlier results on cercariae of a Puerto Rican stock. The basic total number of papillae of both species is the same (62), and the basic numbers of papillae in the various groups are the same: dorsal, 20; ventral, 18; lateral, 10 on each side; and acetabular, 4. The cercariae of these 2 species differ, however, in patterns of papillae, chiefly the dorsal patterns, and can be distinguished from each other.

Schistosoma mekongi sp. n. from man and animals, compared with four geographic strains of Schistosoma japonicum.

Schistosoma mekongi sp. n. is described from man and animals in Cambodia. It is compared to 4 geographic strains of Schistosoma japonicum. It differs from S. japonicum in the size of embryonated eggs, in the length of the prepatent peroid in the mammalian host, and in its utilization of a different snail host. The relative usefulness of conventional morphologic criteria in the differentiation of Asian schistosomes is discussed.

Morphology and life cycle of Schistosoma sinensium Pao, 1959, from northwest Thailand.

Schistosoma sinensium Pao, 1959, was first isolated from an unidentified snail in Szechuan Province, China, and was described on the basis of adult worms and eggs recovered from experimentally infected mice. We discovered snails, Tricula bollingi Davis, and rodents, Rattus rattus (L.) and Crocidura attenuata Milne-Edwards, infected with S. sinensium near Fang in northwest Thailand. Adult worms were recovered from small veins immediately adjacent to the small intestine. Eggs first appeared in the feces of experimentally infected mice at 25 days postinfection. Cercariae first emerged from experimentally infected T. bollingi at 40 days postinfection. Shortly after emerging, cercariae were found at the water surface, their bodies flat against the meniscus and tails hanging free in the water column. Our morphometric results for adults and eggs from naturally infected hosts agree well with those presented in the original description. The occurrence of a lateral spine on the egg of this Asian schistosome has created some confusion as to the affinities of S. sinensium. A comparison of 8 character states, including snail hosts, cercarial behavior, geographical distribution, and morphology of life cycle stages, indicates that S. sinensium is more closely related to S. japonicum Katsurada than it is to S. mansoni Sambon.

Schistosoma malayensis n. sp.: a Schistosoma japonicum-complex schistosome from Peninsular Malaysia.

Schistosoma malayensis n. sp., a member of the Schistosoma japonicum complex is described from Rattus muelleri in Peninsular Malaysia and 2 strains are characterized. The only morphological differences noted among adults from natural hosts were that S. malayensis are in general smaller than S. mekongi and S. japonicum. But these differences may be the result of host-induced variations and therefore are of little taxonomic value. To minimize the effects of host-induced variations, adult worms recovered from laboratory mice with similar worm burdens at 50-56 days postinfection were compared. These comparisons revealed only minor morphometric differences among these 3 species. Schistosoma malayensis eggs from naturally and experimentally infected hosts are most similar to those of S. mekongi, with eggs of both species being, in general, smaller than those of S. japonicum. The egg index for S. malayensis is usually higher than for S. japonicum and lower than for S. mekongi. Differences were noted in the developmental rates in mice for 2 isolates of S. malayensis, S. mekongi, and S. japonicum (Philippine strain), but relatively large differences observed between isolates of S. malayensis indicate that, in this case, the developmental rate is not a useful taxonomic character. Schistosoma malayensis is erected principally on the basis of differences, reported elsewhere, in the life histories and in the electrophoretic migration patterns of isoenzymes of adult worms as compared to S. mekongi and S. japonicum. These comparisons indicate that S. malayensis is more closely related to S. mekongi than to S. japonicum.

The occurrence of Schistosoma mattheei in the south-western Transvaal.

To determine whether Schistosoma mattheei is present in the south-western Transvaal, sixty habitats were searched for the intermediate host snail, Bulinus africanus. Ten populations of this snail were located, 2 of which were infected with S. mattheei. Eggs of one of these isolates, originating from a spring in the Mooi River, were examined with an optical microscope. Scanning electron micrographs of the teguments of adult male worms and the terebratorial membranes of miracidia are described. These parasites are morphologically similar to some previously described from another habitat in the same geographical area and both populations can be regarded as typical S. mattheei.