Schistosoma mansoni and Schistosoma haematobium: identification and characterization of glycoconjugate antigens in the hemolymph of infected vector snails

Two carbohydrate epitopes were identified by monoclonal antibodies (KCS and E2) and characterized with respect to their immunoreactivity, monosaccharide structure, and location. Immunofluorescence demonstrated the presence of both epitopes on the surfaces of sporocysts, cercariae, and miracidia of Schistosoma mansoni, Schistosoma haematobium, and Schistosoma japonicum. However, spatial distribution and density of expression varied among species and developmental stages, and neither epitope was detectable on adult worm surfaces. Both glycans were found in the hemolymph of infected, but not uninfected, intermediate snail hosts. The presence of epitopes in hemolymph, as well as in schistosome eggs, is species-specific for KCS, recognizing only S. mansoni, and partly specific for E2, which reacted predominantly with S. haematobium. Immunoaffinity purification of target antigens for KCS and E2 from hemolymph of infected Biomphalaria and Bulinus, respectively, followed by carbohydrate composition analysis revealed a high content of fucose in both glycans. Methylation analysis demonstrated exclusively terminal fucose for the target antigen of KCS and terminal as well as internal fucose for the one of E2. Removal of terminal fucose abolished reactivity with both monoclonal antibodies. Both glycans are different from previously characterized schistosome carbohydrates. Their biological function(s) remain to be defined.     

Evidence for the presence of active cytochrome P450 systems in Schistosoma mansoni and Schistosoma haematobium adult worms

Extracts of the adult worms of both Schistosoma mansoni and Schistosoma haematobium can metabolise some typical P450 substrates but to differing degrees. S. mansoni worm extracts displayed a approximately 12-fold higher specific activity for an aminopyrine substrate than rat liver microsomes. At 4 mM substrate concentration the demethylation reaction with N-nitrosodimethylamine (NDMA) (5 nmol HCHO/mg protein/min) was only half that of rat liver microsomes, whereas in extracts of S. haematobium, no detectable activity was found towards NDMA. Using ethylmorphine as substrate the demethylation activity of S. mansoni extracts (1.82 nmol HCHO/mg protein/min) was 5.5-fold lower than that of rat liver microsomes. Benzphetamine demethylase activity was also readily detectable in S. mansoni worm extracts at 6.79 nmol HCHO/mg protein/min compared with 10.20 nmol HCHO/mg protein/min in the case of rat liver microsomes. When aniline was used as substrate, surprisingly, no activity was found in worm extracts of either S. mansoni or S. haematobium, whereas rat liver microsomes showed high activity towards this amine. The anti-P450 2E1 and 2B1/2 cross-reacted with both worm homogenates and gave a specific band corresponding to a protein of molecular weight of approximately 50.0 kDa. A study with anti-P450 IVA antibody revealed that while this protein was strongly expressed in S. haematobium worm extracts, no immunoreactivity was observed with extracts of S. mansoni. Immunoblotting analyses with anti-P450 IIIA and P450 1A1 did not detect immunoreactive protein in either S. mansoni or S. haematobium.     

Susceptibility of Iraqi fresh water snails to infection with Schistosoma haematobium and Schistosoma mansoni Egyptian strains

A great number of Egyptian workers and farmers are seeking settlement in Iraq and some of them proved to have either Schistosoma Haematobium (S.h.) or Schistosoma mansoni (S.m) or even mixed infection. Besides, there is the possibility that some of the Iraqi fresh water snails may prove to be susceptible to infection by one or both of the Schistosoma Egyptian strains. The present study deals with investigations on the susceptibility of Iraqi B. truncatus, Gyranaulus ehrenbergi, Physa c.f. fontinalis, Lymnea lagetis, Melanoides tuberculata and Melanopsis nodes by these parasites. Egyptian S. haematobium but not Egyptian S. mansoni infect Iraqi B. truncatus and both proved to be unable to infect any of the other snails included in the study. Yet, the number of cercariae shedded by B. truncatus snails infected with the Egyptian S. haematobium strain, was much less that the number of cercariae shedded by these snails when infected with the Iraqi S. Haematobium strain.     

Reappraisal of experimental infections with cercariae and schistosomula of a Brazilian strain of Schistosoma mansoni in mice.

The present investigation involves a reevaluation of previous results obtained after experimental infection of Swiss Webster mice with cercariae and schistosomula of the Schistosoma mansoni LE strain maintained under laboratory conditions. Three experimental groups of mice were considered: the animals of the first group were percutaneously (ring method) infected with cercariae, those of the second were subcutaneously inoculated with cercariae and the mice of the third were inoculated by the same route with schistosomula transformed in vitro. The data obtained so far indicated that the most effective method of infection is the subcutaneous injection with schistosomula, with a mean adult worm burden recovery of 54.1% when compared to the abdominal percutaneous and subcutaneous routes of infection with cercariae, in which the values were 36.7% and 32.4%, respectively. This suggests that, in experimental infections of SW mice with a LE S. mansoni strain, the skin is to be considered an effective attrition site in the percutaneous route, whereas in the case of inoculation with cercariae, a small amount of larvae fails to be transformed into viable schistosomula, possibly due to skin phase avoidance. A brief discussion about attrition sites and elimination of larval S. mansoni worms in mice is presented.     

Effect of artemether against Schistosoma haematobium in experimentally infected hamsters

The drug, artemether, has been shown to be active against the juvenile stages of Schistosoma japonicum and Schistosoma mansoni in experimentally infected animals, while it is less effective on adult worms. These findings have been confirmed in randomised controlled trials in humans. Consequently, it could be expected that artemether is also active against Schistosoma haematobium. We present here the first results from experiments assessing the effect of artemether on S. haematobium. Hamsters with a single infection received intra-gastrically an initial dose of 300 mg/kg artemether on day 14, 21 or 28, followed by further doses at varying treatment regimens. In all the treatment groups, the total and female worm reduction rates were highly significant, and ranged from 78 to 100% in hamsters harbouring juvenile schistosomes. Hamsters infected three times with S. haematobium, on days 0, 4 and 9, and repeatedly treated with artemether at the same dose as above, showed highly significant total and female worm reduction rates of between 94 and 99%. Artemether was also active against 77-day-old adult S. haematobium, since its administration on two consecutive days resulted in highly significant total and female worm reduction rates of 76-89%. Our findings confirm that artemether is also active against S. haematobium, especially the schistosomules. These results provide a basis for clinical trials in humans, for further assessment of the potential of artemether for schistosomiasis control.     

Influence of intramolluscan larval stages of Echinostoma liei on the infectivity of Schistosoma mansoni cercariae

During co-infection of Biomphalaria glabrata with Schistosoma mansoni and Echinostoma liei, S. mansoni cercariae released before the complete resorption of S. mansoni sporocysts show a very strong decrease of their infectivity in mice. Under conditions of high interspecific competition (i.e. when the snails are infected by E. liei 8 days after infection by S. mansoni), the mean overall worm return is five times lower than that of the control experiment. A marked decrease of the infectivity of cercariae is also noted when snails, infected exclusively with either sporocysts of S. mansoni or rediae of E. liei, are associated in the same tank.     

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.     

Parasitological and histopathological effects of immunosuppression in guinea-pigs (Cavia porcellus) experimentally infected with Schistosoma haematobium

The parasitological and histopathological effects of immunosuppression in guinea-pigs (Cavia porcellus) experimentally infected with Schistosoma haematobium were studied. A total of 16 guinea-pigs were divided into four groups (four per group): non-immunosuppressed, non-infected group (NN); immunosuppressed, non-infected group (IN); immunosuppressed, infected group (II); non-immunosuppressed, infected group (NI). The IN and II groups were immunosuppressed with 5?mg/kg prednisolone while the II and NI animals were infected with 200-300 S. haematobium cercariae. Excretion of eggs in urine/faeces, worm burden and histopathology of some vital organs of the guinea-pigs were studied. Eggs of S. haematobium were observed in the urine of the NI and II groups from 9 weeks post-infection and in faeces from 10 and 13 weeks post-infection for the NI and II groups, respectively. However, II animals excreted more viable eggs in urine and faeces than those of the NI group. Worm recovery at 14 weeks post-infection showed that NI and II guinea-pigs had more female worms than male worms and a greater proportion of worm recovery for NI animals was of immature worms. Significant differences (P?0.05). Histological changes, which were notably reactions to adult S. haematobium worms, were observed in the organs of the NI and II groups but these changes were seen more in the organs of the immunosuppressed, infected (II) than in the non-immunosuppressed, infected (NI) guinea-pigs. The results suggest that immunosuppression before infection increased worm survival and had a moderate effect on liver and bladder histology of S. haematobium infected guinea-pigs.     

Epidemiology of mixed Schistosoma mansoni and Schistosoma haematobium infections in northern Senegal

Due to the large overlap of Schistosoma mansoni- and Schistosoma haematobium-endemic regions in Africa, many people are at risk of co-infection, with potential adverse effects on schistosomiasis morbidity and control. Nonetheless, studies on the distribution and determinants of mixed Schistosoma infections have to date been rare. We conducted a cross-sectional survey in two communities in northern Senegal (n=857) to obtain further insight into the epidemiology of mixed infections and ectopic egg elimination. Overall prevalences of S. mansoni and S. haematobium infection were 61% and 50%, respectively, in these communities. Among infected subjects, 53% had mixed infections and 8% demonstrated ectopic egg elimination. Risk factors for mixed infection - i.e. gender, community of residence and age - were not different from what is generally seen in Schistosoma-endemic areas. Similar to overall S. mansoni and S. haematobium infections, age-related patterns of mixed infections showed the characteristic convex-shaped curve for schistosomiasis, with a rapid increase in children, a peak in adolescents and a decline in adults. Looking at the data in more detail however, the decline in overall S. haematobium infection prevalences and intensities appeared to be steeper than for S. mansoni, resulting in a decrease in mixed infections and a relative increase in single S. mansoni infections with age. Moreover, individuals with mixed infections had higher infection intensities of both S. mansoni and S. haematobium than those with single infections, especially those with ectopic egg elimination (P<0.05). High infection intensities in mixed infections, as well as age-related differences in infection patterns between S. mansoni and S. haematobium, may influence disease epidemiology and control considerably, and merit further studies into the underlying mechanisms of Schistosoma infections in co-endemic areas.     

Studies on experimental mixed infections of Schistosoma mansoni and S. haematobium in hamsters

Golden hamsters were superinfected simultaneously with 100 Schistosoma haematobium cercariae, 1 and 3 weeks after initial infection with 100 S. mansoni cercariae. Results indicate that there was a higher degree of resistance to superinfection with S. haematobium at 1 week following initial infection with S. mansoni than that produced in the other two superinfections. This resistance was evidenced by a reduction in the number and size of worms of both species, decrease in S. haematobium egg extrusion per female and by a striking deviation in the egg distribution pattern of both species. Such an early host resistance was not recorded in previous works. Cross-mating was observed but no hybridization took place and the eggs produced were hatchable and typical of their species.     

Tegumental alterations in juvenile Schistosoma haematobium harboured in hamsters following artemether treatment

We report the findings of a detailed temporal study on tegumental alterations in juvenile Schistosoma haematobium, induced by artemether, using scanning electron microscopy. Hamsters infected with S. haematobium cercariae for 28 days were treated intragastrically with a single dose of 300 mg/kg artemether. Groups of two hamsters were killed 24 h, 72 h and 7 days after treatment, and schistosomula were recovered from livers by perfusion and subsequent systematic examination of the tissue, before routinely processing for scanning electron microscopic examination. Most schistosomula collected 24 h after artemether administration showed severe tegumental damage, usually including swelling, fusion, vesiculation, peeling and collapse of enlarged sensory structures. After 72 h, tegumental damage had increased and schistosomula generally showed contraction with extensive swelling, erosion and peeling of the tegument. Seven days post-treatment, severe tegumental damage was only seen in a single male specimen with swelling of the worm body and destruction of the oral sucker. The other schistosomula showed only light to moderate damage, suggesting that schistosomula surviving the treatment began to recover. Our findings of tegumental damage following artemether treatment correlate with the efficacy of this novel antischistosomal drug in killing the juvenile stages of S. haematobium and complement recent findings with S. japonicum and S. mansoni.     

Schistosoma mansoni: salicylanilides as topical prophylactic against cercarial penetration of mice

Salicylanilide and 37 of its analogs were applied topically to mice as candidate chemoprophylactic agents against Schistosoma mansoni cercarial penetration. The compounds were solubilized in absolute methanol, dimethyl sulfoxide, or isopropanol at concentrations not exceeding 1.25% W/V. The tails of the mice of each experimental group were treated by immersion for 5 min in the test compound solution or in the vehicle. The treated tails of 5 mice from each group were washed for 30 min in flowing tap water 3-4 hr after compound application. Tails of all mice were then exposed to approximately 100 cercariae by tail immersion for 1 hr, 24 hr after treatment. The portal veins were perfused 49 days after exposure and worm burdens were determined. The protective capacity of each compound was calculated by comparing the reduction of the mean worm burdens of the compound treated mice to the worm burdens of those treated with only the vehicle and expressing the resulting value as percentage protection. Of the 38 compounds tested, 20 provided 98% or better protection if the treated tails were not washed before exposure to cercariae. Of these 20 active compounds, 16 provided 98% or better protection from infection by S. mansoni cercariae even after the mouse tails were subjected to the 30 min wash.     

Schistosoma japonicum: the pathology of experimental infection

The pathology of experimental schistosomiasis japonica is reviewed and compared with the pathology of schistosomiasis japonica in man and to some aspects of schistosomiasis mansoni and schistosomiasis haematobia in experimental animals. The induction of granulomas around Schistosoma japonicum eggs depends upon cell mediated immunity, as do the reactions to Schistosoma mansoni and Schistosoma haematobium eggs. However, the modulation of the reaction to S. japonicum eggs can be greatly influenced by antibody, while antibody has no effect on the granulomas around S. mansoni eggs. Adult worm pairs of S. japonicum tend to cluster in the mesenteric venules, and most eggs are laid in a few sites. This leads to large, focal intestinal lesions similar to the discrete lesions produced by S. haematobium in the intestine and urinary tract but in contrast to the widespread, diffuse lesions produced by S. mansoni. Comparison with S. japonicum infection in humans is limited chiefly by our scant knowledge of the pathology produced by S. japonicum in infected persons. Most such comparisons are, in any case, limited by the marked differences in the reactions of various experimental host species to the infection and by differences in the reaction of a given host species to different strains of the parasite.     

Vaccination of mice with a 30 kDa Schistosoma antigen with and without human adjuvant induces high protection against S. mansoni infection

A 30 kDa antigen was characterized as a hydrophobic polypeptide containing 16 amino acids and evaluated as a potential candidate vaccine against infection by Schistosoma mansoni. CD1 albino mice immunized at 0, 14, and 21 days with 25 or 50 microg of the 30 kDa antigen per mouse with and without alum developed high levels of IgG antibodies (predominantly IgG2a and IgG2b isotypes). When immunized mice were infected with 200 S. mansoni cercariae, the highest protection levels (61% and 65% reduction in worm burden in two separate experiments) were obtained using the 50-microg antigen without alum adjuvant. The granuloma size decreased to 10%, a non-significant level in mice immunized using alum adjuvant. The results demonstrate the ability of the 30 kDa antigen with and without alum adjuvant to protect mice against S. mansoni infection.     

Schistosoma mansoni, S. japonicum, S. haematobium: glycogen content and glucose uptake in parasites from fasted and control hosts

The glycogen content of male and female Schistosoma mansoni has been measured in flukes from normally fed hosts and those from fasted hosts. In infections from both the mouse and the hamster, a significant reduction in schistosomal glycogen of males is seen hours after food is withdrawn from the host. Reductions in protein content of the schistosomes were only observed in hamster infections fasted at least 72 hr. The livers of infected mice not only decrease in size during fasting, but there is a concomitant reduction in glycogen per unit wet weight. Comparisons of glycogen:protein ratios of mansonian males, females, and host livers indicate that the fasting-induced loss of liver glycogen is also observed in the male schistosome, but not the female. Studies of both S. mansoni and S. haematobium pairs from fed hosts suggest that the ratio of glycogen:protein contents in the male schistosome correlates with the glycogen:protein ratio of the female partner. Measurements of glucose uptake in vitro suggest that greater uptake rates may be observed in flukes perfused from fasted hosts. In S. japonicum from infected mice, a reduction in male glycogen was also detected as early as after a 6-hr fasting period, but changes in the females were not significant. Unmated male S. japonicum also exhibit a reduction in glycogen levels after fasting, but the quantity of worm glycogen present in these males remains higher than comparable mated males. In mice entrained to a regulated pattern of available food, fluctuations in glycogen content of the male schistosomes were observed, but in the female partners fluctuations were of a smaller magnitude.(ABSTRACT TRUNCATED AT 250 WORDS)     

In vitro and in vivo effects of unsaturated fatty acids on Schistosoma mansoni and S. haematobium lung-stage larvae

Incubation of Schistosoma mansoni lung-stage larvae in 90% corn oil for 6 hr was shown to elicit exposure of their, otherwise masked, apical membrane antigens to binding of anti-schistosome antibodies in the indirect membrane immunofluorescence test (IF). The possibility that unsaturated fatty acids (FA) are responsible for this effect was herein supported by IF data on ex vivo lung-stage larvae of S. mansoni and S. haematobium incubated for 1/2-2 hr with 80% corn oil, 50% olive oil, or 10-20 microM arachidonic acid. Treatment with unsaturated FA followed by filipin staining for cholesterol visualization indicated that unsaturated FA do not induce exposure of schistosomular surface membrane antigens via extraction of surface membrane cholesterol. Evidence using inhibitors and stimulators of neutral sphingomyelinase suggested that unsaturated FA perhaps activate worm tegument-bound neutral sphingomyelinase, leading to sphingomyelin hydrolysis and changes in surface membrane fluidity. Larval apical membrane antigens are, thus, allowed to diffuse freely in the plane of the membrane and bind specific antibodies in IE Excessive sphingomyelin hydrolysis might explain why high FA concentrations or long incubation periods eventually lead to larval death. The significant decrease (P < 0.01) in S. mansoni and increase (P < 0.02) in S. haematobium worm recovery in BALB/c mice given unsaturated FA-high and -poor diets, respectively, indicated these findings have in vivo relevance and led to the proposal that unsaturated FA likely plays a role in natural attrition of S. mansoni and S. haematobium lung-stage larvae.     

Effects of exogenous glucose on survival and infectivity of Schistosoma mansoni cercariae

The effects of exogenous glucose in artificial spring water (ASW) were studied on the survival and infectivity of Schistosoma mansoni cercariae. The mean percent survival of cercariae maintained in 1% glucose in ASW for 36 and 48 hr was significantly greater than that of cercariae maintained identically in ASW. Cercariae maintained in ASW with or without glucose for 24 hr, fixed in neutral buffered formalin, and stained in Oil Red O, showed an accumulation of neutral lipid in the tail. Cercariae maintained as described above and stained in periodic acid-Schiff exhibited depleted glycogen, mainly from the tail. Cercariae maintained in ASW with glucose for 24 hr did not resynthesize glycogen. Cercariae maintained in ASW with glucose for 24 hr were as capable of infecting male FVBN202 mice as were freshly emerged cercariae, and increased the percent of worm recovery. Exogeneous glucose added to ASW prolonged the survival of S. mansoni cercariae and increased infectivity in terms of worm recovery.     

Comparison of two Egyptian strains of Schistosoma mansoni in hamsters

In human infection with Schistosoma mansoni from Beni-Suef, the eggs were encountered more frequently in the urine of patients than in infection with S. mansoni from Giza, where eggs were passed into the stool. A comparative study of the two strains of S. mansoni from Beni-Suef and Giza has been carried out in golden hamster. Consistent strain differences were observed. The Beni-Suef strain proved to have lower worm recovery and different egg distribution patterns in tissues of infected hamsters. Worms of both sexes of this strain were larger in size and required a longer period to reach maturity. Hence, the prepatent period was prolonged. Significant differences between the two strains were also noted in the number of eggs per worm. A lower mortality rate and a longer survival time were encountered in hamsters infected with the Beni-Suef strain.     

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。     

Transplantation of Schistosoma japonicum daughter sporocysts in Oncomelania hupensis

Schistosoma japonicum daughter sporocysts obtained from infected Oncomelania hupensis hupensis were successfully transplanted to parasite-free O. hupensis hupensis. Survival and infection rates of recipient snails were 80% and 75% respectively. Intramolluscan development of transplanted daughter sporocysts in recipient snails appears to proceed in a similar manner as those reported for transplanted S. mansoni and S. haematobium in their respective snail intermediate hosts. Complete colonization of the digestive gland of recipient snails by sporocysts was observed 80 days after transplantation. Cercarial production during a 10-day observation from recipient snails was characterized by periods of high and low and irregular daily emissions. The average daily cercarial production was 150 per snail. Cercariae produced by recipient snails were infective to mice. Of those cercariae exposed to mice, approximately 30% developed to adult schistosomes. These results have definitive utility in the maintenance of S. japonicum in the laboratory.