Schistosoma mansoni: Antischistosomal activity of the four optical isomers and the two racemates of mefloquine on schistosomula and adult worms in vitro and in vivo

Recent studies have shown that mefloquine (MQ) reveals interesting antischistosomal properties. We examined the antischistosomal activities of the erythro and threo isomers and racemates of MQ on newly transformed schistosomula (NTS) and adult Schistosoma mansoni in vitro and in mice harbouring adult S. mansoni. The in vitro effects in the presence and absence of haemin were monitored by means of microcalorimetry, scanning electron microscopy and phenotypic evaluation. Incubation of NTS with the erythro derivatives at concentrations of 3 μg/ml and above resulted in convulsions, granularity, decrease in heat flow, and death while NTS incubated with the threo derivatives were only affected at high concentrations (100 μg/ml). Extensive tegumental alterations, decrease in metabolic activity, viability, and death were observed when adult schistosomes had been exposed to 10 μg/ml of the erythro compounds. Moderate tegumental and viability changes but reduced heat production rates were observed with the threo derivatives at 10 μg/ml. In the presence of haemin, all MQ derivatives showed pronounced antischistosomal properties against adult S. mansoni in vitro. In vivo, MQ derivatives achieved statistically significant total and female worm burden reductions ranging between 65.4% and 100%. The highest total worm burden reductions of 93.4% and 90.2% were observed following treatment with the erythro and threo racemates, respectively. In conclusion, the optical isomers and racemates of MQ show only moderate stereoselectivity, in particular in vivo. Our results may enhance our understanding of the mechanism of action and therapeutic profile of MQ derivates on schistosomes.     

血吸虫病感染特征及其免疫病理机制的研究进展

血吸虫病是由血吸虫病裂体吸虫属血吸虫引起的一种寄生虫病,分布范围广,广泛分布在热带及亚热带的贫困偏远地区,其在公共卫生方面的重要性仅次于疟疾,该病已经造成了大量的残疾和死亡。据世界卫生组织(WHO)血吸虫病专家委员会1984年统计,全球感染血吸虫人口已达2亿。血吸虫种类繁多,寄生于人体的有6类,其中埃及血吸虫、曼氏血吸虫和日本血吸虫是主要的致病种类。血吸虫卵是血吸虫病的主要致病因子,寄生于宿主组织中的虫卵使宿主发生免疫病理反应,导致泌尿生殖系统(埃及血吸虫)炎症和梗阻性疾病、肠道疾病、肝脾炎症和肝纤维化(曼氏血吸虫和日本血吸虫)的发生。没有得到有效控制的早期血吸虫病发展到晚期,可引起包括上消化道出血、肝性脑病(日本血吸虫和曼氏血吸虫)、膀胱鳞状细胞癌(埃及血吸虫)和不孕不育症在内的严重并发症,主要对血吸虫病流行病学、临床表现、临床分期、并发症、致病机制及其免疫病理机制作一综述。     

Schistosoma japonicum: treatment of different developmental stages in mice with long-acting praziquantel implants

This paper reports the effective treatment of Schistosoma japonicum in a mouse model with long-acting praziquantel (PZQ)-loaded poly(ε-caprolactone) implants. The implants yielded stable, high plasma PZQ concentrations ranging 100–1600 ng/mL during the 40-day investigation period. For assessment of efficacy, the implants were implanted into mice immediately after infection and at 1, 2, 3 and 4 weeks after infection to treat the schistosomes at different developmental stages. All the mice were sacrificed at 6 weeks after infection for worm and egg recovery, worm morphology examination, and histopathological analysis of implantation site tissues. The worm burdens, egg burdens, and numbers of miracidia hatched from the retrieved eggs for all the implant-treated groups (except groups T2-A, T4 and T5) were reduced by 100% when compared with the control group. From groups T2-A, T4 and T5, some schistosome debris was recovered. Eggs were found in only group T5 for which the time between infection and implantation was 4 weeks, which enabled the maturation of juvenile female schistosomes into adult ones that lay eggs. Histopathological observations of implantation tissue showed no evidence of granulomatous foreign-body or lymphoid cell aggregation, demonstrating good biocompatibility of the PZQ implants. These results demonstrate that the long-acting PZQ implants can kill schistosomes at any developmental stages and attenuate/avoid the associated liver damage.     

Existence of host DNA sequences in schistosomes--horizontal and vertical transmission

The localization of repetitive DNA sequences in the mouse genome such as mouse type 2 Alu sequence (B2) and mouse retrovirus-related sequences was shown in the body of adult Schistosoma japonicum and Schistosoma mansoni by applying an in situ PCR and hybridization technique. Using the same method, mouse major histocompatibility complex (MHC) class I sequence was also found in schistosomes. Furthermore, mouse MHC class I sequence and type A retroviral sequence were detected in S. japonicum and S. mansoni cercarial DNA by blot hybridization. These findings indicated that horizontal and vertical transmission of host DNA sequences occurred in schistosomes. The incorporation and propagation of host sequences in schistosomes and the roles played by such host sequences form the focus of this brief review.     

Biomphalaria species in Alexandria water channels

Of the several species of Biomphalaria snails worldwide that serve as the intermediate host for Schistosoma mansoni, Biomphalaria alexandrina is a species that is indigenous to Egypt. Recently, there has been much debate concerning the presence of Biomphalaria glabrata and the hybrid of the species with Biomphalaria alexandrina. Due to this debate, the absence of a clear explanation for the presence of B. glabrata in Egyptian water channels and the probability that they may be reintroduced, we conducted this field study to identify Biomphalaria species present in Alexandria water channels. Laboratory-adapted susceptible snails to Schistosoma mansoni of the following species were used as a reference; Biomphalaria alexandrina, Biomphalaria glabrata and their hybrid. These snails were used to perpetuate the Schistosoma life cycle at the Theodor Bilharz Research Institute (TBRI), Cairo, Egypt. Morphological and molecular studies were conducted on these reference snails as well as on the first generation of Biomphalaria snails from two areas in the Alexandria governorate. The morphological study included both external shell morphology and internal anatomy of the renal ridge. The molecular study used a species-specific PCR technique.The results demonstrated that there was an absence of Biomphalaria glabrata and the hybrid from Alexandria water channels. Moreover, the susceptibility patterns of these reference snails were studied by measuring the different parasitological parameters. It was found that Biomphalaria glabrata and the hybrid were significantly more susceptible than Biomphalaria alexandrina to the Egyptian strain of Schistosoma mansoni. The results demonstrated that if Biomphalaria glabrata was reintroduced and adapted to the local environment in Egypt, it would have important epidemiologic impacts that would have a serious effect on the health of Egyptian people.     

Differential adhesive properties of the surface of human blood flukesSchistosoma mansoni

While infecting a vertebrate host, blood flukes (Schistosoma mansoni) must continually resist adhesions by immune effector cells. However, the male and female schistosomes must adhere to one another in order to establish and maintain the sexual pairing process after 4 wk postinfection. Using a contact angle method, the relative adhesiveness of male and female parasites were determined. Results indicate that schistosomes restrict effector cell adhesion through developmental, sexual, and regional differences in adhesive properties.     

Oral immunization with Salmonella harboring a Sm14-based DNA vaccine does not protect mice against Schistosoma mansoni infection

The protection against Schistosoma mansoni infection was evaluated in SWISS mice orally vaccinated with an attenuated strain of Salmonella carrying a Sm14-based DNA vaccine. Although this formulation was not able to afford a reduction in the worm burden, a non-antigen-specific decrease in schistosome-induced granulomatous reaction was verified in livers of mice that received Salmonella.     

Tissue responses exhibited by Biomphalaria alexandrina snails from different Egyptian localities following Schistosoma mansoni exposure

Snails’ susceptibilities to infection with Schistosoma mansoni were determined through observation of infection rates, total cercarial production and tissue responses of the first generation (F1) of Biomphalaria alexandrina snails, originally collected from different Egyptian governorates (Giza, Fayoum, Kafr El-Sheikh, Ismailia and Damietta) and responses were compared between groups. The emergence of cercariae for a 3-month period and the calculation of survival and infection rates, in control (Schistosome Biological Supply Center; SBSC) and infected snails were evaluated. SBSC and Giza snails showed greater susceptibilities to infection and lower mortality rates. In addition, at 6 and 72 h post-exposure to miracidia all the snail groups showed no difference in the anatomical locations of sporocysts. The larvae were found in the head-foot, the mantle collar and the tentacles of the snails. Sporocysts showed normal development with low tissue reactions in SBSC and Giza snail groups infected with S. mansoni miracidia (SBSC). However, in Fayoum, Kafr El-Sheikh, Ismailia and Damietta snail groups, variable tissue responses were observed in which numerous hemocytes made direct contact with S. mansoni larvae forming capsules. The results suggested that, different responses of B. alexandrina snail’s hemocytes towards S. mansoni are related to the degree of susceptibility of these snails. So this is important in planning the strategy of schistosomiasis control.     

Glycotope analysis in miracidia and primary sporocysts of Schistosoma mansoni: Differential expression during the miracidium-to-sporocyst transformation

Fucosylated carbohydrate epitopes (glycotopes) expressed by larval and adult schistosomes are thought to modulate the host immune response and possibly mediate parasite evasion in intermediate and definitive hosts. While previous studies showed glycotope expression is developmentally and stage-specifically regulated, relatively little is known regarding their occurrence in miracidia and primary sporocysts. In this study, previously defined monoclonal antibodies were used in confocal laser scanning microscopy, standard epifluorescence microscopy and Western blot analyses to investigate the developmental expression of the following glycotopes in miracidia and primary sporocysts of Schistosoma mansoni: GalNAcβ1-4GlcNAc (LDN), GalNAcβ1-4(Fucα1-3)GlcNAc (LDN-F), Fucα1-3GalNAcβ1-4GlcNAc (F-LDN), Fucα1-3GalNAcβ1-4(Fucα1-3)GlcNAc (F-LDN-F), GalNAcβ1-4(Fucα1-2Fucα1-3)GlcNAc (LDN-DF), Fucα1-2Fucα1-3GalNAcβ1-4(Fucα1-2Fucα1-3)GlcNAc (DF-LDN-DF), Galβ1-4(Fucα1-3)GlcNAc (Lewis X) and the truncated trimannosyl N-glycan Manα1-3(Manα1-6)Manβ1-4GlcNAcβ1-4GlcNAcβ1-Asn (TriMan). All but Lewis X were variously expressed by miracidia and sporocysts of S. mansoni. Most notably, α3-fucosylated LDN (F-LDN, F-LDN-F, LDN-F) was prominently expressed on the larval surface and amongst glycoproteins released during larval transformation and early sporocyst development, possibly implying a role for these glycotopes in snail–schistosome interactions. Interestingly, Fucα2Fucα3-subsituted LDN (LDN-DF, DF-LDN-DF) and LDN-F were heterogeneously surface-expressed on individuals of a given larval population, particularly amongst miracidia. In contrast, LDN and TriMan primarily localised in internal somatic tissues and exhibited only minor surface expression. Immunoblots indicate that glycotopes occur on overlapping but distinct protein sets in both larval stages, further demonstrating the underlying complexity of schistosome glycosylation. Additionally, sharing of specific larval glycotopes with Biomphalaria glabrata suggests an evolutionary convergence of carbohydrate expression between schistosomes and their snail host.     

Molecular cloning and expression of a Schistosoma japonicum tegumental membrane-associated antigen from Japanese strain

Diagnosis and vaccine development form the major focus in creating strategies for the control of schistosomiasis. In this study, we established an IgG1 mouse monoclonal antibody (MoAb), SJA111, which strongly reacted with 23–25-kDa Schistosoma japonicum tegumental-associated membrane proteins, but not with eight other parasitic antigens. A λgt 11 cDNA library from the Japanese strain of the Schistosoma japonicum adult worm was screened with SJA111 as a probe. A single positive clone was isolated and the nucleotide sequence of the isolated cDNA was determined. The cDNA clone consisted of 844 bp, and the coding region contained 576 bp which was translated to a 22.6-kDa protein. This region showed 99.0% and 99.3% significant homology with those of the Chinese and Philippine strains of Schistosoma japonicum, respectively. The deduced amino acid sequence of the protein was identical to that of the Philippine strain and only one residue differed from that of the Chinese strain. The recombinant form of the tegumental protein was expressed in Escherichia coli and purified by a combination of ion exchange and affinity chromatography, and the purified protein was found to react with the sera of patients infected with Schistosoma japonicum. This result suggests that this antigen may be useful in the immunodiagnosis of schistosomiasis as well as in the development of an effective vaccine.     

Human helminth co-infection: No evidence of common genetic control of hookworm and Schistosoma mansoni infection intensity in a Brazilian community

Strong statistical associations between soil-transmitted helminths and schistosomes are frequently observed in co-endemic human populations, although the underlying explanations remain poorly understood. This study investigates the contribution of host genetics and domestic environment to hookworm and Schistosoma mansoni infection intensity and evaluates the role of genetic and non-genetic factors in co-variation of infection intensity. Detailed genealogical information allowed assignment of 1303 individuals living in the Brazilian community of Americaninhas, Minas Gerais state, to 25 pedigrees (containing between two and 1159 members) residing in 303 households. The prevalence of co-infection with both hookworms and schistosomes was high (38.5%), with significant correlation between Necator americanus and S. mansoni faecal egg counts. Bivariate variance component analysis demonstrated a modest but significant species-specific heritability for intensity of N. americanus (h² = 0.196) and S. mansoni infection (h² = 0.230). However, after accounting for demographic, socio-economic and household risk factors, no evidence for common genetic control of intensity of hookworm and schistosome infection was observed. There was some evidence for residual clustering within households but the majority (63%) of the covariance between N. americanus and S. mansoni infection intensity remained specific to the individual and could not be explained by shared genes, shared environment or other shared demographic, socio-economic or environmental risk factors. Our results emphasize the importance of exposure to hookworm and schistosome infection in driving the association between levels of infection with these species in hosts resident in areas of high transmission and suggest that much of this common exposure occurs outside the home.     

Vaccine potential of hemocyanin from Oncomelania hupensis against Schistosoma japonicum

Hemocyanin, a giant oxygen transport protein which is usually found in many arthropods and mollusks was isolated and purified from Oncomelania hupensis. In this study, we showed that Oncomelania hupensis hemocyanin (OhH) shared carbohydrate epitopes with different developmental stages of Schistosoma japonicum (Cercaria, Schistosomulum, Adult worm and Egg) and exhibited serological cross-reaction with these stages of S. japonicum immune sera, which had a potential for use in diagnostic and therapeutic studies of schistosomasis. OhH was used as a vaccine in combination with Freund's adjuvant to evaluate the induction of immune responses and protection against S. japonicum infection in mice. Mice immunized with OhH induced a Th1 type of immune responses. Strong protection against S. japonicum were observed in adult worm and egg burdens after 42 days post-challenge, which showed a significant worm reduction of 52.5% and egg reduction of 69.2% compared to the control groups, respectively. These results indicated that OhH was a potential candidate to compose an anti-schistosome vaccine.     

Conservation of protein kinase a catalytic subunit sequences in the schistosome pathogens of humans

cAMP-dependent protein kinases (PKAs) are central mediators of cAMP signaling in eukaryotic cells. Previously we identified a cDNA which encodes for a PKA catalytic subunit (PKA-C) in Schistosoma mansoni (SmPKA-C) that is required for adult schistosome viability in vitro. As such, SmPKA-C could potentially represent a novel schistosome chemotherapeutic target. Here we sought to identify PKA-C subunit orthologues in the other medically important schistosome species, Schistosoma haematobium and Schistosoma japonicum, to determine the degree to which this potential target is conserved and could therefore be exploited for the treatment of all forms of schistosomiasis. We report the identification of PKA-C subunit orthologues in S. haematobium and S. japonicum (ShPKA-C and SjPKA-C, respectively) and show that PKA-C orthologues are highly conserved in the Schistosoma, with over 99% amino acid sequence identity shared among the three human pathogens we examined. Furthermore, we show that the recently published Schistosoma mansoni and S. japonicum genomes contain sequences encoding for several putative PKA substrates with homology to those found in Homo sapiens, Caenorhabditis elegans, and Saccharomyces cerevisiae.     

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.     

Antischistosomal action of thioxo-imidazolidine compounds: an ultrastructural and cytotoxicity study

Schistosomiasis is a disease caused by helminthes of the genus Schistosoma, which threatens approximately 207 million people worldwide. Recently, strains of Schistosoma mansoni appear to be developing tolerance and resistance against Praziquantel, the most commonly available drug on the market used in the treatment of disease. This worrisome development justifies studies that seek alternatives for the prevention, treatment and cure of this disease. This study aimed to evaluate the in vitro activity of new imidazolidine compounds 1-benzyl-4-[(4-chloro-phenyl)-hydrazono]-5-thioxo-imidazolidin-2-one (LPSF/PT-5) and 1-(4-chloro-benzyl)-4-[(4-fluoro-phenyl)-hydrazono]-5-thioxo-imidazolidin-2-one (LPSF/PT-11) against adult worms of S. mansoni. LPSF/PT-5 and LPSF/PT-11 imidazolidine derivatives showed relevant schistosomicidal activity in vitro and induced significant ultrastructural alterations in worms and cell death: results similar to praziquantel. Thus, it is possible that these imidazolidine derivatives can be future candidates as schistosomotic drugs, but further studies are needed to elucidate the induced mechanisms behind this response.