Comparison of the surface morphology of adult Schistosoma japonicum (Chinese, Philippine and Indonesian strains) by scanning electron microscopy

Comparative ultrastructural observations of the Egyptian schistosomes: Schistosoma mansoni and Schistosoma haematobium

An ultrastructural topography has been made to the tegumental architectures of two Egyptian schistosomes namely S. mansoni and S. haematobium hosted in a model animal namely Cricentus auratus. The distribution of sensory papillae on the oral sucker were arranged in one circle around the rim in addition to some papillae in upper part of inner zone in male, female S. mansoni and in male S. haematobium. The differences in the types of papillae, their distribution and shape of ridges on various parts of the body surface which are quite specific for each species was studied. Also, the ventral tegument of female's displays larger and more numerous sensory papillae. Both ciliated and non-ciliated papillae were observed in this work which makes a link with another species of schistosome S. japonicum. Another characteristic feature in this study is unique of male of S. haematobium, the extensive formation of ridges and transformation to microvilli in the posterior region in males. These finding may provoke further study of schistosomes hosted in animal model for more detailed investigation at the molecular level.

Schistosoma japonicum IAP and Teg20 safeguard tegumental integrity by inhibiting cellular apoptosis

Schistosomes are causative agents of human schistosomiasis, which is endemic in tropical and subtropical areas of the world. Adult schistosomes can survive in their final hosts for several decades, and they have evolved various strategies to overcome the host immune response. Consequently, understanding the mechanisms that regulate parasitic cell survival will open avenues for developing novel strategies against schistosomiasis. Our previous study suggested that an inhibitor of apoptosis protein in Schistosoma japonicum (SjIAP) may play important roles in parasitic survival and development. Here, we demonstrated that SjIAP can negatively regulate cellular apoptosis in S. japonicum by suppressing caspase activity. Immunohistochemistry analysis indicated that SjIAP ubiquitously expressed within the worm body including the tegument. Silencing of SjIAP expression via small interfering RNA led to destruction of the tegument integrity in schistosomes. We further used co-immunoprecipitation to identify interaction partners of SjIAP and revealed the tegument protein SjTeg-20 as a putative interacting partner of SjIAP. The interaction between SjIAP and SjTeg-20 was confirmed by a yeast two-hybrid (Y2H) assay. Moreover, results of a TUNEL assay, RNA interference, scanning and transmission electron microscopy, caspase assays, transcript profiling, and protein localization of both interacting molecules provided first evidence for an essential role of SjIAP and SjTeg-20 to maintain the structural integrity of the tegument by negatively regulating apoptosis. Taken together, our findings suggest that the cooperative activities of SjIAP and SjTeg-20 belong to the strategic inventory of S. japonicum ensuring survival in the hostile environment within the vasculature of the final host.

Schistosomiasis is a worldwide public health concern particularly in developing countries. The causative agents, schistosomes, can survive within the vascular system of their final hosts for several decades despite facing the host’s immune response. Therefore, elucidating the mechanism of cell survival will contribute to the understanding of host-parasite interaction and may lead to the identification of suitable targets for developing novel strategies against schistosomiasis. Inhibitor of apoptosis proteins are highly conserved proteins functioning as endogenous inhibitors of apoptotic cell death. Here, we demonstrated that an inhibitor of apoptosis protein of Schistosoma japonicum (SjIAP) governs the integrity of the tegument of schistosomes by inhibiting cellular apoptosis of the parasite. Further studies revealed that SjTeg-20, an S. japonicum tegumental protein, cooperates with SjIAP to inhibit apoptosis in schistosomes. Our findings provide new insights into the role of SjIAP and SjTeg-20 in maintaining the integrity of the worm tegument by negatively regulating apoptosis.

A circular analysis of chronobiology of Schistosoma japonicum cercarial emergence from hilly areas of Anhui, China

About 46 mammal species have been suspected as reservoir hosts for Schistosoma japonicum and therefore the track of the target parasites, in relation to definitive host species, may be of great importance in terms of theoretical and practical implications. The circadian rhythm of cercariae emergence, a genetically controlled behavior for parasites to adapt to their definitive hosts, may seem to be a perfect biological marker for S. japonicum. In this study, a late (or nocturnal) cercarial emergence pattern was observed on the parasites from one hilly region in Anhui of China, where rodents serve as reservoirs, and on the first generation of the parasites. Moreover, by using the circular statistics, the homogeneity of parasites in such trait was also demonstrated. All these provide evidence for the genetically controlled biological trait, which seems essential in the investigation of macro- or micro-dynamics of parasite transmission of interest. This is particularly true in the case of S. japonicum when multiple parasite isolates or strains are more likely to exist.

Morphological and morphometric study of cercariae and adult worms of Schistosoma mansoni (SLM strain) isolated from infected mice

In northeastern Brazil, the schistosomiasis is historically endemic and considered as a public health problem. The Schistosoma mansoni São Lourenço da Mata (SLM-PE, Brazil) strain was used in several paper already published; however, morphological and morphometric studies about this strain was never done. In this work, scanning electron microscopy (SEM) was used in morphological and morphometric analysis of cercariae and adult worms. Cercariae were obtained from Biomphalaria glabrata snails and adult worms from mice, both infected by the S. mansoni SLM strain, fixed and prepared for SEM. The results showed that cercariae of S. mansoni measures 254.9 μm of length. The bodies are covered by spines, with a ventral sucker, an oral sucker with sensory receivers, and a pair of penetration glands in the head. The area of tail and body and the distance between suckers were 3,011.77, 1,530.32, and 42.9 μm, respectively. Adult worms of S. mansoni were divided into three main regions: the anterior, medial, and posterior, besides the gynecophoral canal in males. The measure of adult worms of S. mansoni was 4 mm males and 5 mm females. The anterior region length of the male was 470 μm and of the female 271 μm. All the parameters were assayed in ten samples. The morphometric values found in the SLM strain were smaller than other S. mansoni strains described in the literature as well as other helminths. This is the first morphological and morphometric study with the SLM strain of S. mansoni being extremely important for improving control strategies and life quality of the local population.

Conservation of CD4+ T cell-dependent developmental mechanisms in the blood fluke pathogens of humans

Schistosoma blood flukes are trematode parasites with a cosmopolitan distribution that infect over 200 million people globally. We previously showed that Schistosoma mansoni growth and development in the mammalian host is dependent on signals from host CD4+ T cells. To gain insight into the mechanisms that underlie this dependence, we sought to determine the evolutionary origins and limits of this aspect of the host-pathogen relationship. By infecting RAG-1-/- mice with a range of different schistosome species and strains, we tested several hypotheses concerning the time during Schistosoma evolution at which this dependence arose, and whether this dependence is specific to Schistosoma or is also found in other blood flukes. Our data indicate that the developmental dependence on CD4+ T cells previously described for S. mansoni is conserved in the evolutionarily basal species Schistosoma japonicum, suggesting this developmental adaptation arose early in Schistosoma evolution. We also demonstrate that the development of the more evolutionarily derived species Schistosoma haematobium and Schistosoma intercalatum are dependent on adaptive immune signals. Together, these data suggest that the blood fluke parasites of humans utilise common mechanisms to infect their hosts and to co-opt immune signals in the coordination of parasite development. Thus, exploitation of host-schistosome interactions to impair or prevent parasite development may represent a novel approach to combating all of the schistosome pathogens of humans.

Oligonucleotide microarray analysis of strain- and gender-associated gene expression in the human blood fluke, Schistosoma japonicum

Schistosomiasis is a chronic and debilitating disease caused by blood flukes (digenetic trematodes) of the genus Schistosoma. Schistosomiasis japonica, a zoonosis caused by Schistosoma japonicum, is endemic to the Philippines and China. We utilised a 22,575 feature custom oligonucleotide DNA microarray designed from public domain databases of schistosome-expressed sequence tags to explore differential gene expression between the Philippine (SJP) and Chinese (SJC) strains of S. japonicum, and between male and female S. japonicum. We found that 593, 664 and 426 probes were differentially expressed between the two geographical strains when we compared mix sexed adults, male worms and female worms. Additionally, the study revealed that 1163 male- and 1016 female-associated probes were differentially expressed in SJP whereas 1047 male- and 897 female-associated probes were differentially expressed in SJC. The study greatly expands previously published data of strain and gender-associated differential expression in S. japonicum. Further, these new data provide a stepping stone for understanding the complexities of the biology, sexual differentiation, maturation, and development of human schistosomes, signaling new approaches for identifying novel intervention and diagnostic targets against schistosomiasis.

Revisiting the question of limited genetic variation within Schistosoma japonicum

Recent electrophoretic data have indicated that Schistosoma japonicum in mainland China may be a species complex, with the existence of a cryptic species being predicted from the analysis of schistosome populations from Sichuan province. To investigate the Sichuan form of S. japonicum, 4.9 kbp of mitochondrial DNA from each of three samples of the parasite from China (two from Sichuan and one from Hunan) and one from Sorsogon in the Philippines were amplified, sequenced and characterized. The sequence data were compared with those from the related South-east Asian species of S. mekongi (Khong Island, Laos) and S. mlayensis (Baling, Malaysia) and that from S. japonicm from Anhui (China). At both the nucleotide and amino-acid levels, the variation among the five S. japonicum samples was limited (< 1%). This was consistent with the conclusions drawn from previous molecular studies, in which minimal variation among S. japonicum populations was also detected. In contrast, S. mekongi and S. malayensis, species recognized as separate but closely related, differ from each other by about 10%, and each differs by 25%-26% from S. japonicum. Phylogenetic trees provided a graphic representation of these differences, showing all S. japonicum sequences to be very tightly clustered and distant from S. mekongi and S. malayensis, the last two being clearly distinct from each other. The results thus indicate no significant intra-specific genetic variation among S. japonicum samples collected from different geographical areas and do not support the idea of a distinct form in Sichuan.

Schistosoma japonicum myosin: cloning, expression and vaccination studies with the homologue of the S. mansoni myosin fragment IrV-5

The Schistosoma japonicum homologue of the 62 kDa fragment of S. mansoni myosin (SmIrV-5), which has proved highly protective against S. mansoni infection in mice and rats, has been cloned and expressed as the full length 62 kDa equivalent, Sj62, and a truncated 44 kDa version, Sj44. DNA sequencing showed the Sj62 sequence to be 88.4% identical at the nucleic acid level and 96% identical in deduced amino acid sequence to that of SmIrV-5. The recombinant proteins (rSj44 and rSj62) were strongly recognized in Western blotting by sera from mice multiply vaccinated with UV-irradiated S. japonicum cercariae and weakly recognized by S. japonicum chronic infection mouse sera. Unlike SmIrV-5, mouse antisera against the recombinant S. japonicum proteins did not give positive recognition in immunofluorescence assay with the surface of newly transformed schistosomula of the homologous species, S. japonicum, nor did they react with S. mansoni schistosomula. However, the anti-rSj62 sera clearly localized the native antigen to the subtegumental muscle layers in male adult worm sections by immunoelectron microscopy. Vaccination of several groups of mice and/or rats with rSj44 and rSj62 incorporated into different adjuvants induced high titres of specific IgG but in only one experimental group was there a significant reduction in worm burden (27%, P < 0.05). The possible reasons for the disparity between the vaccination results presented here and those demonstrated in experiments using rSm62 (IrV-5) are discussed.

A biological and immunological comparison of Chinese and Philippine Schistosoma japonicum

A comparison was made of the host (BALB/c mice)-parasite relationship of a Chinese mainland (Anhui) strain and Philippine (Sorsogon) strain of Schistosoma japonicum. Differences in fecundity, infectivity, prepatency, host survival and susceptibility to praziquantel were examined. The mean percentage of worms establishing was 40.0 and 34.4% for Chinese and Philippine S. japonicum, respectively. Egg laying commenced on days 26 and 28 after infection with the Chinese or Philippine strain, respectively. Significant differences in the total number of eggs and number of eggs per worm pair laid were observed. In terms of the number of eggs per worm pair and host survival, the Chinese strain was more virulent than the Philippine in BALB/c mice. Praziquantel treatment reduced worm burdens by 80-90% in both strains. No significant differences were observed in murine antibody responses against the 2 strains. Irradiated Chinese cercarial vaccines were protective only against homologous challenge; irradiated Philippine cercarial vaccines were not protective, confirming earlier findings that this strain is neither able to induce nor able to act as a target of irradiated cercariae-mediated vaccination. Antibody responses and immunoblot profiles in vaccinated mice were similar, regardless of the strain of parasite used.

Electrophoretically-detected allozyme variation reveals only moderate differentiation between Chinese and Philippine Schistosoma japonicum

A number of discrete strains of Schistosoma japonicum have been described of which those from China and the Philippines are the most important in terms of public health significance. The strains have previously been shown to differ in a number of biological characteristics and isoenzyme analysis has established that Chinese and Philippine S. japonicum are, especially, quite distinct. As few direct genetic differences have been identified, with nuclear and mitochondrial genetic markers being shown earlier to be highly conserved between the two forms (Bowles et al., 1993), enzyme electrophoresis was performed to re-evaluate whether the two strains are as genetically diverse as field and laboratory maintained isolates previously examined using this approach. Some allelic differences were evident between Chinese and Philippine S. japonicum but the genetic distance (a measure of genetic relatedness), D = 0.272, between the two strains was, however, considerably smaller than the earlier obtained estimates of D > 0.4-0.575. In addition to the enzyme studies, restriction patterns, obtained using 4-base cutting restriction enzymes and hybridisation with DNA probes comprising the entire ribosomal DNA (rDNA) repeat unit of S. mansoni, were indistinguishable between the Chinese and Philippine forms of S. japonicum, thereby re-emphasising their remarkable similarity at the genetic level.

Nuclear and mitochondrial genetic markers highly conserved between Chinese and Philippine Schistosoma japonicum

Geographical isolates of S. japonicum, and particularly isolates from China and the Philippines, were examined at the molecular level for genetic divergence. Sequences from both nuclear and mitochondrial genomes were selected as markers of evolutionary divergence and S. mekongi and S. mansoni were included in the study for comparison purposes. Restriction fragment length polymorphism (RFLP) and PCR-RFLP analysis of the rDNA repeat unit and sequence analysis of the second internal transcribed spacer region (ITS2) within the rDNA repeat and the cytochrome c oxidase I (COI) gene of the mitochondrial genome were performed. No intra-specific variation in S. japonicum was found in the rDNA repeat and only very slight variation was detected within the COI sequence. A survey of the entire genome, using random amplified polymorphic DNA (RAPD) analysis, again showed that Chinese and Philippine S. japonicum are remarkably similar at the DNA sequence level. We were thus unable to obtain direct molecular evidence in support of previous findings, particularly those based on isoenzyme analysis, that a very high level of intra-specific variation exists in S. japonicum.

Opisthorchis viverrini: changes of the tegumental surface in newly excysted juvenile, first-week and adult flukes

The tegumental surface of the newly excysted juvenile, first-week and adult stages of a human liver fluke, Opisthorchis viverrini, was studied by scanning electron microscopy. The surface of the newly excysted juvenile is characterized by circumferentially arranged ridges alternated with troughs which bear rows of spines encircling the body. These spines are characterized by the shapes of their edges: the first type with serrated edge appears on the anterior part, and the second type with single sharp edge appears on the middle part. There are no spines on the posterior part of the body. Three types of presumed sensory papillae are present: type A is a single small cone-shaped ciliated papilla; type B is a group of ciliated papillae on a common dome-shaped base; and type C is a large papilla with nonciliated bulb. Type A papillae are scattered evenly on the surface but are more concentrated around the oral and ventral suckers, as well as the excretory pore. Pairs of both type A and B papillae are located in rows along the lateral surfaces of the body. Type C papillae are located solely on the lip of the ventral sucker. In the first-week fluke the tegumental surface appears corrugated and covered with short developing microvilli, and spines are mostly lost. In the fully-grown adult fluke the surface appears highly corrugated with wave-like folds encircling the body which are covered in turn with closely packed stubby microvilli. Microvilli are more numerous and are taller on the ventral than on the dorsal surface. Among microvilli on the surface of both older stages three types of sensory papillae as in the newly excysted juvenile were observed, but they are of larger sizes. The number of type A papilla increases whereas that of type B papilla decreases during maturation. The distribution of papillae in both stages is similar to the newly excysted stage.

Molecular variation in the human schistosomes

It is now recognised that intraspecific variation is widespread in the human schistosome species. This review evaluates recent advances in the detection and characterisation of variants within the human schistosomes and the implications of this variation in terms of infectivity and development in intermediate and definitive hosts, drug responsiveness, pathogenicity and immunogenicity. It also examines advances in the methods used to detect variation and highlights the use of genetic approaches, notably enzyme electrophoresis and, especially, the recent application of DNA methods. Molecular techniques, such as restriction fragment length polymorphism (RFLP) analysis, polymerase chain reaction (PCR) and DNA sequencing are now proving invaluable for distinguishing species and strains of schistosomes and recent progress in this remarkably dynamic area is emphasised.