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PubMed1980

Infectivity in rodents of Schistosoma mansoni cercariae of human and murine origin.

Experimental infections of white laboratory mice and wild rats (Rattus rattus) with cercariae of Schistosoma mansoni of different descent, whether murine or human, demonstrate that there is no significant difference in the probability of maturation of these cercariae into adult schistosomes. These results enable us to hypothesize that the reverse would be true, i.e. that cercariae of murine or human descent would be capable of infecting man with the same success rate. Circulation of the parasite from man to the rat and from the rat to man may therefore occur in natural habitats, which does not mean that rodents can maintain indefinitely and independently Schistosoma mansoni, nor does it mean that murine strains may not evolve locally.

Animals↗
PubMed1977

Investigations of the unimiracidial infection of Schistosoma intercalatum in snails and the infection of the final host using cercariae of one sex.

Infection with single miracidial doses of Schistosoma intercalatum from Cameroun in Bulinus forskalii and from Zaire in B.globosus resulted in an equal number of male and female infections. The cercarial production of both sexes started at the same time. The male infected snails produced a greater number of cercariae, because of the longer duration of infection. The recovery of schistosomes from infection with male and female cercariae was for S. intercalatum, Zaire, 38.8 +/- 10.6 and 18.7 +/- 14.0 respectively. For S. intercalatum from Cameroun, with single sex cercariae from two different populations of intermediate hosts from Zaire and Cameroun were 38.3 +/- 7.3 (male); 20.3 +/- 9.3 (female) and 35.0 +/- 8.7 (male); 12.2 +/- 4.5 (female), respectively.

Animals↗
PubMed1987

The effect of light and darkness on the production of cercariae of Schistosoma haematobium from Bulinus globosus.

The cercariae of Schistosoma haematobium showed a diurnal periodicity of emergence from Bulinus globosus in a twelve hour light/dark cycle. Peak emission occurred at 11.00 hrs with a smaller peak at 20.00 hrs, following the start of the period of darkness. In continuous illumination this second peak was not seen, indicating that only the morning peak is circadian in origin. The evening peak occurs in response to dark treatment and can be produced by periods of darkness ranging from eight seconds to one hour. The longer the period of dark treatment the longer the rise in output is maintained on return to light conditions. Subjection of snails to periods of dark treatment during the normal light period caused a reduction in the evening peak with the largest effect seen following the longest period of darkness. An increased output of cercariae was seen following fifteen minutes exposure to a range of light intensities, the largest increase occurring at 10,000 and 7000 lux and complete darkness. The rapidity of this reaction to variations in light intensity suggests that the cercariae of S. haematobium are showing emergence in response to shadows.

Animals↗
PubMed1985

Comparison of the protective resistance induced by 60Co-irradiated cercariae and schistosomula of the WFFS and NMRI strains of Schistosoma mansoni.

Mice, CBA/HT6T6 and C57BL/10, were vaccinated with 1 X 350 or 1 X 500 Schistosoma mansoni cercariae or schistosomula attenuated with 20 or 56 krad 60Co irradiation and challenged with 200 cercariae. Protective resistance against homologous strain challenge was compared using the Winches Farm Field Station (WFFS) and Naval Medical Research Institute (NMRI) strains of S. mansoni. Maximal resistance to challenge was obtained in both strains of mice with cercariae or schistosomula of either WFFS or NMRI strain attenuated with 20 krad. Protection using organisms attenuated with 56 krad was significantly lower. Since previous studies with the two parasite strains have shown that the biological effects of irradiation are similar, the difference in the immunogenicity of the 56 krad-irradiated NMRI strain in this study from earlier studies must be due either to different local conditions for irradiation or to adaptation of the NMRI strain to a new laboratory environment. This finding may have important implications for vaccination studies and investigations of the mechanisms of immunity where radiation-attenuated parasites are used.

Animals↗
PubMed1975

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.

Animals↗
PubMed1976

Transformation of cercariae to schistosomula: a quantitative comparison of transformation techniques and of infectivity by different injection routes of the organisms produced.

Six transformation techniques ((1) incubation of cercariae in isotonic medium; (ii) penetration of isolated skin; (iii) stimulation with crude egg lecithin; (iv) mechanical disruption by passage through a syringe and 21 gauge needle; (v) by whorling of cercariae with a vortex mixer; (vi) syringe transformation followed by incubation) were evaluated. The organism produced were assessed for infectivity for mice by 6 different routes of infection (percutaneous, intradermal, subcutaneous, intra-peritoneal, intravenous and intra-muscular). At perfusion the largest numbers of adult worms were recovered from mice injected intramuscularly with organisms produced by the syringe technique and control mice given cercariae percutaneously. The peak for migration of schistosomula (following syringe transformation and intramuscular injection) through the lungs and the appearance of adult worms in the mesenteries was shown to be similar to cercarie administered percutaneously.

Animals↗
PubMed1975

Schistosoma mansoni: in vitro conversion of cercariae to schistosomula.

Schistosoma mansoni cercariae were incubated for 3-5h at 37 degrees C in various test solutions, and the rate and extent of conversion of the cercariae to schistosomula were determined. Criteria used to identify schistosomula included: (1) loss of cercarial tail, (2) viability of organisms in saline but not in water, (3) pre-acetabular gland evacuation and (4) ability to survive in culture. Incubation of cercariae in rat chamber fluid resulted in organisms which were water sensitive, but retained their tails and pre-acetabular gland contents. Conversion to water sensitivity was not blocked by 0-01 M EDTA.

Animals↗
PubMed1977

Experimental investigations on the behaviour of the cercariae of an ectoparasitic digenean Transversotrema patialense: general activity patterns.

The activity patterns of the cercariae of Transversotrema patialense have been examined by monitoring the behaviour of individual larvae. Records of three different behavioural modes, namely active, tail-first swimming, passive dropping and resting periods were made separately. The age- and temperature-dependence of the activity patterns during the spontaneously active life of the cercariae were examined and estimates made of the absolute speeds of swimming and dropping. Through the temperature range 25--32 degrees C, the spontaneously active life of cercariae declined from about 18 h to about 6 h. Within this interval, after an initial period of high activity rates, a gradual decline in activity followed. The decline was a result of a decreasing frequency of swimming events rather than any change in the durations of such events. The neural control and energetic significance of the cercarial activity patterns are discussed.

Animals↗
PubMed1983

Schistosoma mansoni: the structure and elemental composition of pre-acetabular penetration gland cell secretion in pre-emergent cercariae.

The structure and elemental composition of the secretory products of the pre-acetabular penetration gland cells of pre-emergent cercariae of Schistosoma mansoni have been investigated at an ultrastructural level using X-ray probe microanalysis. The secretion contains 2 types of bodies, one homogeneous and one heterogeneous with electron-lucent areas. Using a variety of fixation and sectioning techniques it has been shown that the apparent electron density of the homogeneous bodies (Type B) is the result of interaction with osmium tetroxide and stain. The small electron-lucent areas of the other type of secretory body (Type A) represent regions where granules have been leached out by processing media. X-ray analysis of cercariae still within sporocysts has indicated that these granules are very rich in calcium, and it is suggested that the calcium is absorbed by the developing cercariae through the sporocyst wall from the molluscan haemolymph.

Animals↗
PubMed1987

The induction of species-specific immunity against Schistosoma japonicum by exposure of rats to ultra-violet attenuated cercariae.

Single percutaneous immunizations of Fischer rats with 1000 ultra-violet attenuated Schistosoma japonicum cercariae induced 52-88% resistance to challenge 4 weeks later. Increasing this to 3 immunizations induced 90% resistance to challenge, and this level of protection remained undiminished for up to 40 weeks after vaccination. Rats vaccinated with gamma-irradiated S. mansoni cercariae were resistant to challenge with S. mansoni but not S. japonicum. Similarly rats vaccinated with u.v.-attenuated S. japonicum cercariae were not resistant to heterologous challenge. Thus irradiated vaccines are species-specific in both permissive and non-permissive hosts.

Animals↗
PubMed1982

Localized skin changes at the site of immunization with highly irradiated cercariae of Schistosoma mansoni are associated with enhanced resistance to a challenge infection.

The level of immunity to a percutaneous cercarial challenge with Schistosoma mansoni was assayed 4-6 weeks after immunization of mice with highly irradiated (20 krad.) cercariae or schistosomula. When immunization and challenge occurred through the same skin site, resistance, particularly that which occurred in the skin, was greater than that observed when immunization and challenge occurred in different sites. The enhanced resistance is believed to be due to localized changes in the skin; 4 weeks after exposure to irradiated cercariae, abdominal skin is characterized by a thickened epidermis, changes in the ground substance and a cellular infiltration of the dermis. A convenient mouse model is described in which one or both ear pinnae are exposed to irradiated cercariae and a percutaneous challenge is given via the abdomen, thus eliminating the effects of local skin changes. In this model, the majority of the challenge infection which succumbs to the immune response appears to be killed in the skin.

Animals↗
PubMed1980

The survival of the cercariae of Schistosoma mansoni in relation to water temperature and glycogen utilization.

Survival curves for cercariae of Schistosoma mansoni maintained at different temperatures were determined. Between 15 and 35 degrees C the curves were of reverse sigmoid form and the probit transformation gave a statistically good fit. The slope of the regression lines fitted to the probit transformation increased exponentially as the temperature rose. Above 35 degrees C heat intolerance became important and increased exponentially as the temperature rose. Below 15 degrees C, cold intolerance caused an initial high level of mortality followed by an extended period with insignificant mortality. The glycogen content of whole cercariae and separated cercarial bodies and tails was measured during ageing. The glycogen content of whole cercariae declined exponentially during ageing. This was a product of exponential decreases in the glycogen content of both the body and the tail of the organism. The cercarial tail was shown to contain slightly over half of the total glycogen content. The rate of glycogen use was higher in the tail than in the body. A computer simulation model was used to demonstrate that the observed exponential use of glycogen could generate survival curves similar to those observed experimentally.

Aging↗
PubMed1984

Passive transfer of resistance and the site of immune-dependent elimination of the challenge infection in rats vaccinated with highly irradiated cercariae of Schistosoma mansoni.

The immune-dependent elimination of a challenge infection in rats vaccinated with highly-irradiated cercariae of Schistosoma mansoni was analysed by passive transfer of serum, recovery of the challenge from the lungs and liver and by transferring lung-stage schistosomula. Recipients of serum from rats immunized with either unirradiated, 20 or 40 krad.-irradiated cercariae, most of which die in the liver, lungs and skin, respectively, were equally resistant if the serum was injected on the day of infection or 5-7 days after infection. In addition, vaccinated rat serum transferred to mice and vaccinated rabbit serum transferred to rats conferred comparable protection when injected on day 0 or 5 days after infection of the recipients. This apparent susceptibility of the lung schistosomula to immune attack was confirmed by challenging 20 or 40 krad.-irradiated cercariae vaccinated rats with lung-stage schistosomula derived either from mice or rats. All the detectable attrition of a cercarial challenge in vaccinated rats occurred between 7 and 10 days post-challenge, before the parasites reached the liver. Since there was no evidence of damage or attrition in the skin or lungs before day 7 it was concluded that immune-dependent elimination occurred rapidly following a 'window of sensitivity' coinciding with the migration of the parasites from the lungs to the liver.

Animals↗
PubMed1991

Penetration of stimuli of fish skin for Acanthostomum brauni cercariae.

The cercaria of Acanthostomum brauni penetrates the skin of its fish host in response to a combination of two chemical signals from the fish skin surface: free fatty acids and a macro-molecular mucus component. The latter seems to be a protein, as the penetration-stimulating activity of fish skin surface mucus is eliminated by digestion with proteinase, but not by digestion with glycosidases, nor by a removal of glycosaminoglycans. These penetration-stimulating host signals differ from the glycoproteins that stimulate the attachment of A. brauni cercariae to the host and also from the macromolecular fish host signals which have been found to stimulate the attachment and penetration by Opisthorchis viverrini cercariae.

Animals↗
PubMed1991

The transition from an aerobic to an anaerobic energy metabolism in transforming Schistosoma mansoni cercariae occurs exclusively in the head.

It has been shown that in intact cercariae of Schistosoma mansoni in water, both head and tail had an identical, aerobic energy metabolism. As long as the environment was water, glucose was mainly degraded to carbon dioxide by both head and tail whether or not these two were still connected to each other. Transfer of intact cercariae into a simple salt medium supplemented with glucose resulted in a very rapid transition towards a more anaerobic energy metabolism: the production of lactate and pyruvate increased, whereas the production of carbon dioxide remained more or less constant. A concomitant rise in temperature to 37 degrees C was not essential for this biochemical transition, but made it more pronounced. Experiments on isolated cercarial bodies and tails in a transforming medium demonstrated that the tail oxidized glucose to carbon dioxide, whereas bodies produced mainly pyruvate and lactate. The results showed that the metabolic transition towards a more anaerobic energy metabolism occurred only in the head and not in the tail of the cercariae. Loss of the tail was shown not to be a pre-requisite for this transition, nor did it by itself trigger a metabolic switch in the resulting cercarial body.

Aerobiosis↗
PubMed1993

Immunization of pigs against infection with Schistosoma japonicum using ultraviolet-attenuated cercariae.

Since pigs are important in the zoonotic transmission of schistosomiasis japonica in China, a veterinary vaccine might contribute to the control of the disease in humans. Pigs were immunized with three doses each of 10,000 cercariae of Schistosoma japonicum attenuated with ultraviolet light (400 microWatt.min/cm2). The experiment was performed with portable irradiation equipment in a rural area of the Hubei Province (P.R. China). A challenge infection of 1,000 untreated cercariae was given 2.5 or 6 months after the last immunization, and age-matched naive pigs were challenged as a control. Immunized pigs developed about 90% resistance against the challenge. The liver egg load of these animals was reduced by over 90%. Less than 0.01% of the immunizing cercariae developed to adult parasites and the vaccination had no apparent adverse influence on the pigs' health.

Animals↗
PubMed1988

Host-finding in Trichobilharzia ocellata cercariae: swimming and attachment to the host.

The cercaria of Trichobilharzia ocellata finds and identifies its duck host with a series of different behavioural phases. Dispersal and selection of the water surface as microhabitat is achieved by an intermittent swimming behaviour, which is governed by the interplay of passive dropping with forward and backward swimming movements and includes a positive phototactic and a geonegative orientation. Then the cercariae tend to cling to the water surface in an energy-saving resting position. A movement towards the duck feet as the site of entry occurs when shadows evoke forward swimming movements, which are directed away from the source of light, i.e. normally downwards. Forward swimming movements are also stimulated by touch, but only in free-swimming cercariae and not when these are in the resting position. Attachments occur only when a substrate is touched during forward swimming movements. Attachments are stimulated by warm substrates (1 degrees C temperature difference triggers a nearly maximal response) and by chemical components of duck-foot skin, and the readiness to attach is increased when the forward swimming movement is started by shadow stimuli.

Animals↗
PubMed1988

Changes in the organization of the surface membrane upon transformation of cercariae to schistosomula of the helminth parasite Schistosoma mansoni.

Merocyanin 540 (Mc540) is a fluorescent compound which is thought to bind to membranes in which there are substantial amounts of lipid in the lipid-crystalline phase. It is shown here to be of value in detecting the transformation by both mechanical and skin-penetration methods of the cercaria to the schistosomulum. The cercaria does not appear to bind Mc540, but the schistosomulum, binds Mc540 initially, in its anterior region, and at later times over the entire surface. The suggestion that transformation involves changes in the surface membrane lipid phase from gel to liquid-crystalline phase is supported by fluorescence recovery after photobleaching results with 5-N-(octadecanoyl)-amino fluorescein, a lipophilic dye which appears to be immobile in the cercaria, but fully mobile in the 40 min schistosomulum.

Animals↗