The chemical stimuli of human skin surface for the attachment response of Schistosoma mansoni cercariae

and 1986. The chemical stimuli of human skin surface for the attachment response of S mansoni cercariae. International Journal for Parasitology 16: 575–579. The stimuli for the S. mansoni attachment response were analysed by offering skin extracts and chemicals to cercariae through Millipore filters. The attachment stimulating components were contained in the hydrophilic skin extract. Whereas sugars had no stimulating activity, a mixture of electrolytes, lactate and urea had a weak, and amino acids a very strong, effect. The amino acids of the hydrophilic skin extract were qualitatively and quantitatively identified and their effectivity as pure chemicals compared with that of the skin extract. The acid amino acids and histidine and ornithine had a weak effect, whereas arginine alone stimulated as intensely as the whole hydrophilic skin extract. The specialization on arginine as the main attachment trigger could be interpreted as adaptation to the fact that creeping and penetrating cercariae secrete arginine with the contents of their post acetabular glands. Thus they might communicate their successful host identification to further cercariae.     

Further studies on the carbohydrate metabolism of immature Schistosoma mansoni

Further studies on the carbohydrate metabolism of immature Schistosoma mansoni. International Journal for Parasitology 3: 783–787. Analysis of whole cercariae, cercarial bodies and tails and schistosomula shows the tail contains 26 per cent of the cercarial nitrogen, 46 per cent of the glycogen and 59 per cent of the cytochrome oxidase. 32 per cent of the total nitrogen and 22 per cent of the glycogen of the cercarial body is lost during penetration. Oxygen uptake of adult worms but not of cercariae increases between 30 and 37°C. A temperature of 41°C partly inhibits cercarial oxygen uptake but not that of adult worms. Incubation of schistosomula, 21-day-old and adult worms in nitrogen increases the rate of glycolysis.     

The effect of sublethal concentrations of the molluscicide niclosamide on the infectivity of Schistosoma mansoni cercariae.

Experiments were conducted to assess the effect of sublethal concentrations of niclosamide on the infectivity of Schistosoma mansoni cercariae. Exposure of cercariae to 0.02 mg/l and 0.05 mg/l of niclosamide, respectively, for only two hours increased their mortality during penetration of mammalian host skin. The observed increase in mortality in the skin resulted in a consequent reduction of adult worm recovery from the liver and mesenteric veins of animals infected with the treated cercariae.     

A comparative study of the death of schistosomula of Schistosoma haematobium and Schistosoma mansoni in the skin of mice and hamsters.

This study shows that some cercariae of S. haematobium and S. mansoni die during penetration of mouse or hamster skin. Approximately 30-38% of cercariae of both species die in mouse skin and 14-16% die in hamster skin. The greater number of cercariae which die in the skin of mice seems to account for the higher yield of adult worms recovered in hamsters. Adult worm recoveries from animals infected with S. haematobium were, however, only about half the worm recoveries from hosts infected with S. mansoni.     

A comparison of the glycolipid compositions of cercarial and adult Schistosoma mansoni and their associated hosts

Glycolipid patterns of cercarial and adult Schistosoma mansoni were determined and compared with those of Biomphalaria glabrata snails and mouse (BALB/c strain) red blood cells by high-performance thin-layer chromatography. Differences in glycolipid content were found between cercariae and adult worms and between these stages and their respective host tissues.     

Surface proteins on schistosomula and cercariae of Schistosoma mansoni

The surface proteins of schistosomula and cercariae of Schistosoma mansoni were examined by lactoperoxidase catalysed iodination followed by polyacrylamide gel electrophoresis. Two polypeptide chains were clearly labelled and they were present on both cercarial and schistosomular surfaces. A number of minor labelled components were also observed. The results suggest that membranes of the teguments of cercariae and schistosomula are similar.     

Circadian Pattern of Cercarial Emergence in Schistosoma Mansoni(Platyhelminthes: Digenea) from Isolated Biomphalaria Glabrata

The present work aimed to compare the acrophases (peak hours) of emergence of Schistosoma mansoni cercariae among isolated individuals of the snail Biomphalaria glabrata. Laboratory stocks of melanic B. glabrata from the same biotope as the S. mansoni strain (Belo Horizonte, Minas Ger-ais) were used. Twenty-two snails individually exposed to five miracidia were tested. Chronobiological trials were performed outdoors after an acclimation period of at least a week. Three groups of snails were tested between November 1989 and April 1991. Cercarial emergence from individual isolated snails was quantified every 3 h for 3 consecutive days. In all trials, most cercariae were found to emerge during daytime (94.9%). Time series and chronograms showed recurrent peaks during the daytime. The periodogram suggested that 24 h was the period that best fitted cercarial emergence data in 90.9% of the snails. The single cosinor analysis confirmed 24-h rhythms in 95.5% of the snails. Acrophases of cercarial emergence among individual snails occurred between 14:15 and 17:02. They did not differ significantly. The population cosinor analysis indicated greater homogeneity in the 24-h rhythms of cercarial emergence than in the snail groups of each chronobiological trial. Acrophases of cercarial emergence occurred between 14:53 and 15:27 and did not differ significantly among all trials. Data from the three trials were pooled and analyzed using the population cosinor. This statistical method indicated a homogeneity in the 24-h rhythms of cercarial emergence from all snails, with acrophase occurring around 15:00. Results showed that the acrophases of cercarial emergence of S. mansoni are similar among isolated B. glubrura specimens. Data support the hypothesis of a “gate” rhythm in the dynamics of cercarial production and emergence. It is suggested that the adaptive importance of the “gate” mechanism is associated with the concentration of cercariae in the water at times when the vertebrate is present, optimizing the contact between the parasite and the host. The emergence of some cercariae at night (5.1% of the total number of emerged cercariae) suggests a flexible “gate” that could be associated with a residual light effect or with experimental procedures in the laboratory.     

Host identification by Schistosoma japonicum cercariae

Attachment, the first phase of host identification by Schistosoma japonicum cercariae, can occur in 2 different ways. Cercariae clinging to the water surface simply swing around and transfer to the host skin. Free-swimming cercariae behave like S. mansoni: upon touching a substrate, they switch from tailward to forward movement, swim in an arc, and attach to it with the penetration organ. Neither type of attachment is influenced by chemical, thermal, or specific mechanical stimuli from the host. The second phase, remaining on the host, requires a solid hydrophobic surface and seems to depend only on the cercaria's ability to cling to it. This phase is not influenced by chemical or thermal stimuli. The third phase, creeping across the host surface, is independent of chemical and mechanical stimuli. Cercariae migrate in thermal gradients to a preferred temperature of 37 +/- 3 C and then attempt to penetrate. Penetration, the fourth phase, was evoked by human skin surface lipids. The free fatty acid (FA) fraction was identified as exclusively stimulating components. Saturated FA's were effective at chain lengths between 10 and 14 carbon atoms (pH 7.0), and unsaturated FA's were effective at longer chains and their activity increased with increasing number of double bonds. Dog skin surface components did not stimulate cercarial penetration, which can be attributed to the lack of free FA's. A temperature of 32-40 C also stimulated penetration responses, which might be the main stimulus in animal hosts, whose skin surfaces contain no or only a few free FA's. FA's and heat evoked a transformation of cercarial tegument simultaneous with penetration behavior, making the organisms osmotically sensitive. The host identification of S. japonicum cercariae is very nonspecific compared with the differentiated host recognition of S. mansoni.     

日本血吸虫尾蚴钻穿不同宿主皮肤时新转变童虫的死亡情况

日本血吸虫尾蚴在钻穿7种哺乳动物宿主皮肤而转变为童虫时,均发生了自然死亡,而且童虫的死亡率依宿主种类或同一种类的不同品系而异。它们皮肤内平均童虫死亡率分别为:小鼠3.7—7.2％、大鼠6.3％、金黄仑鼠7.0％、长爪沙鼠5.1％、豚鼠6.9％、兔4.9％、恒河猴12.8％。实验证明日本血吸虫尾蚴亦能钻入不易感的鸟类——鸽的皮肤,虽有1/4童虫立即在其皮肤内发生死亡,但部分童虫可移行至肺,然后在肺中消亡。     

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.     

Cross-reactivity between Necator americanus and Schistosoma mansoni in mice.

, , and 1992. Cross-reactivity between Necator americanns and Schistosoma mansoni in mice. International Journal for Parasitology 22: 1143–1149. Poly-parasitism is common in endemic communities and reactivity of sera from hookworm-infected patients against schistosomular antigens has been reported. Protective cross-immunity between N. americanus and S. mansoni was investigated in NIH and BALB/c mice. Protective resistance to homologous challenge with both parasites was confirmed in this model, however, functional immunity to heterologous challenge was not demonstrated. Sera from animals which had received homologous challenge with N americanus and from hookworm-infected mice, which had previously been exposed to radiation-attenuated S. mansoni, exhibited an enhanced IgGAM response to infective stage N. americanus somatic antigens. The implications of these results with respect to serodiagnosis are discussed.     

Production of monoclonal antibodies against target schistosomal antigen secreted in the urine of Schistosoma mansoni-infected patients

This study was undertaken to develop an immunodiagnostic test of active human schistosomiasis mansoni using a monoclonal antibody which targets urinary schistosomal antigen. Polyclonal antisera raised in rabbits against the processed urine of Schistosoma mansoni-infected patients showed very high and significant reactivity with ES product of ova compared with other different S. mansoni antigens. The monoclonal antibody (4.23) was reactive with repetitive epitopes of S. mansoni soluble egg antigen and ES product of ova with molecular mass range of 65–23 kDa and 80–23 kDa, respectively. It recognised different stages of the parasite life-cycle, with no cross reaction with Fasciola or hydatid antigen. MAbs were characterised by isotyping, immunoelectrophoresis, SDS–PAGE and the enzyme-linked immunoelectrotransfer blot technique, ELISA, and their recognition of carbohydrate or protein antigenic epitopes by periodate oxidation and trichloroacetic acid treatment of the antigen. It was used for detection of circulating schistosomal antigen in an antigen capture antibody sandwich ELISA on sera and urines of 58 S. mansoni-infected patients, 17 S. haematobium-infected patients, 15 parasite-free negative healthy controls and sera from 13 schistosomiasis-free patients harbouring Fasciola or hydatid infections. The percentage sensitivity of the assay in the serum of S. mansoni-infected patients was 98.4% and in urine 94.8%. A positive correlation was found between the number of faecal S. mansoni eggs and the circulating antigen, both in serum and in urine. Antigen circulating in urine correlated with that in the sera of S. mansoni patients. These data provide a sensitive and non-invasive method almost comparable with the use of sera for immunodiagnosis of schistosomiasis and an indirect way to reflect the intensity of infection. Australian Society for Parasitology.     

Effect of ultraviolet radiation on survival, infectivity and maturation of Schistosoma mansoni cercariae

S. mansoni cercariae exposed to ultraviolet radiation for 1, 3, 5, 10 and 20 s as well as non-irradiated cercariae remained actively motile 30 min post-irradiation. Thereafter the activity decreased with increasing dose level of radiation and age of cercariae. There was no significant difference between the rates of attachment of the batches of cercariae. The recovery rates (0-49% of cercariae to which mice were exposed) of adult worms were, however, significantly different from the number of cercariae calculated to have attached to the mice (93.5-100% of cercariae to which mice were exposed). Maturation and penetration rates were dependent on radiation exposure levels. Numbers of eggs deposited in the liver of mice as well as hatchability rate of eggs varied significantly with the levels of exposure to radiation.     

Schistosoma mansoni: Vaccination of mice with highly X-irradiated cercariae

Vaccination against schistosomiasis with highly X-irradiated Schistosoma mansoni cercariae was studied in mice. The optimum dose of X radiation for the attenuation of cercariae was in the range of 24–48 krad. In selecting the optimum dose, lesions caused by migrating schistosomula in the lungs of the immunized host were considered. Cercariae exposed to 48 krad caused fewer lesions than those exposed to 24 krad but still effected a comparable worm reduction. The percentages of worm reduction in mice immunized with 48-krad X-irradiated cercariae increased with the number of immunizations up to the fifth immunization and then fluctuated in the sixth, seventh, and eighth days without increase. The optimum dose of immunizing cercariae was 500, and the optimum time interval for successive immunizations was 4 weeks. There was no significant difference in susceptibility to infection in the adult mice 161 to 694 days of age. The duration of acquired immunity in immunized mice is long, still evident 545 days from the last immunization. The present studies clearly showed that with the bioengineering method, the worm reduction in the immunized mice reached 91.1%, the effect of immunization was stronger in mice immunized with the highly X-irradiated cercariae than with the low X-irradiated cercariae, and X-irradiated cercariae were demonstrated to be a strong inducing agent for immunity in mice.     

Schistosoma mansoni: human skin ceramides are a chemical cue for host recognition of cercariae

Schistosoma mansoni cercariae recognize the human host with a sequence of behavioral responses particularly to chemical host cues. After attaching to the skin surface, cercariae are stimulated by so far unknown skin components to hold enduring contact with the skin and to start creeping towards entry sites. We studied the chemical stimulus of human skin for the cercarial enduring contact response by fractionation of human and pig skin surface extracts and offering the fractions to the cercariae via membrane filters. Enduring contact was stimulated exclusively by ceramides, specific lipids of the uppermost skin layers. This chemical cue differs from the 6 chemical host signals used by S. mansoni cercariae in other behavioral steps of host invasion, and thus underlines the specialization of S. mansoni cercariae particularly in chemical host signals. All together, the enduring contact response of the cercariae is, like the other phases of host invasion, well adapted to the chemical properties of human skin.     

Host reactions in Biomphalaria glabrata to Schistosoma mansoni miracidia, involving variations in parasite strains, numbers and sequence of exposures

M-line Biomphalaria glabrata snails are susceptible to Puerto Rican (PR-1) strain of Schistosoma mansoni, but are resistant to a St. Lucian (LC-1) strain. 10-R2 B. glabrata snails are resistant to both strains of S. mansoni. When 10-R2 snails were exposed repeatedly to PR-1 S. mansoni miracidia for 5 consecutive days, all of the sporocysts were encapsulated and destroyed by the snails. Thirty-four per cent of sporocysts examined in M-line snails with similar exposures were also degraded. In double concurrent infections of M-line B. glabrata with [³H]leucine-labeled and unlabeled PR-1 and Lc-1 S. mansoni, the incompatible Lc-1 miracidia were selectively attacked and destroyed. This destruction occurred irrespective of the sequence of exposure of the 2 strains of miracidia, and whether or not the miracidia were labeled. Successful superinfection of M-line B. glabrata with homologous S. mansoni miracidia was obtained at least 4 days after the primary exposure to the miracidia.     

Penetration of human skin by the cercariae of Schistosoma mansoni: an investigation of the effect of multiple cercarial applications

It has previously been postulated that L-arginine emitted by penetrating Schistosoma mansoni cercariae serves as an intraspecific signal guiding other cercariae to the penetration site. It was suggested that penetrating in groups offers a selective advantage. If this hypothesis is correct and group penetration at one site on the host offers an advantage, it would follow that at such a site, successive groups of cercariae would be able to penetrate skin in either greater numbers or at a faster rate. This prediction was tested by the use of an in vitro model of cercarial penetration based on the Franz cell and using human skin. It was demonstrated that there was no increase in the percentage of cercariae able to penetrate the skin with subsequent exposures. Consequently, it seems unlikely that the release of L-arginine by cercariae during penetration could have evolved as a specific orientation system based on a selective advantage offered by group penetration.     

Schistosoma mansoni: topochemical features of cercariae, schistosomula, and adults

The teguments of developing and mature cercariae, recently transformed, and 1-wk-old schistosomula and adult worms were examined for the ultrastructural location of macromolecular carbohydrates and polyelectrolytes. The surface of mature cercariae within sporocysts and cercariae released from the snail is covered by a filamentous coat which reacts with cytochemical reagents for the demonstration of vicinal glycols, but neither the coat nor the surface of the tegument plasmalemma binds cationic colloidal iron at low pH.Upon penetrating mammalian skin, the cercaria sheds its surface coat; the tegument surface of newly transformed schistosomula, older schistosomula and adult worms stains en bloc with acidic colloidal iron, as does the tegument plasmalemma of mature cercariae if the overlying filamentous coat is first removed by physicochemical means. The cercarial coat thus serves to mask anionic groups at the surface of the tegument plasmalemma which become functionally exposed after penetration of the mammalian host. The distribution of colloidal iron binding sites coincides with those for the carbohydrate-complexing phytohemmagglutnin, concanavalin A, which suggests that these membrane-fixed anions are acid mucopolysaccharides, glycoproteins or glycolipids. Carbohydrate-containing material was also localized within membrane-bound vesicles of the tegument matrix and perikarya of developing cercariae and postcercarial schistosomes, suggesting that surface mucosubstances contributing to the tegument glycocalyx of these worms are elaborated, at least in part, by the tegument itself.     

Diplostomum spathaceum cercariae respond to a unique profile of cues during recognition of their fish host

During its normal life cycle, Diplostomum spathaceum cercariae attach to and invade fish intermediate hosts. They are also known to attach to various other aquatic animals in response to water currents, touch and carbon dioxide. The purpose of this study was to identify the specific stimuli used by D. spathaceum cercariae to recognise the appropriate fish host. We characterised the host cues which stimulate them to remain on the host (enduring contact) and to penetrate the skin. Cercariae were exposed to animal skin tissues and fish skin surface mucus, their extracts and chemical modifications integrated into agar or offered via membrane filters. Enduring contact was stimulated by hydrophilic extracts Mr<3kDa, which were sensitive to oxidation of carbohydrates. The stimulating cues are probably small molecular carbohydrates, as monosaccharides stimulated enduring contacts, but amino acids, urea, electrolytes and peptides did not. Penetration was stimulated by hydrophilic macromolecules, Mr>30kDa, and by lipids. The hydrophilic stimuli were protease resistant and precipitable with Alcian blue and they were sensitive to alkaline cleavage, to digestion with lysozyme and neuraminidase as well as to oxidation of sialic acids. They were considered to be glycoproteins with O-glycosidically linked carbohydrate chains and bound sialic acids as signal structures. The lipophilic penetration stimuli were contained exclusively in the fatty acid fractions, and the stimulating characteristics of these fatty acids resembled the stimulating penetrations in other cercarial species. Diplostomum spathaceum cercariae respond to a unique profile of cues in their sequence of host-recognition phases. These cues differ from those used in other fish parasites studied to date and underline the diversity of fish recognition strategies.     

Invasion of skin by Schistosoma cercariae

Schistosomiasis caused by Schistosoma spp. remains a major global health problem affecting >200 million people. The success of these parasites is a result of their adaptation to several different environments, including snail tissue, fresh water and mammalian blood; and their ability to switch between these environments rapidly. The initial step in infection of the human host involves penetration of the human skin by the aquatic form of Schistosoma, the cercaria. This aspect of host invasion is remarkable because no wounds or insect vectors are required and cercariae can penetrate through intact skin rapidly. The mechanisms of host finding and invasion represent fascinating and complex biological phenomenon, which are discussed here.