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PubMedDate not supplied

[Schistosoma mansoni: the levels of infectivity for intermediate host mollusks in Brazil].

The levels of infectivity of Schistosoma mansoni for the three species of Biomphalaria, intermediate hosts of parasite in Brazil were studied after exposing of molluscs to miracidia in the laboratory and in the field. The LE and SJ strains of S. mansoni, maintained in laboratory were used in these experiments as well as the WVS and RFS strains obtained from faeces of schoolchildren from Belo Horizonte, MG. The results show the high level of infectivity of S. mansoni for B. glabrata with infection rates varying from 4.7 to 85.5%. The snail B. straminea was susceptible to LE, SJ and WVS strains, with infection rates of 11.0 to 24.6%, B. tenagophila was susceptible only to LE and SJ strains with infection rates of 2.5 to 6.5%. The mean number of cercariae of the WVS strain shed per day, by B. straminea and B. glabrata were 93 +/- 59 and 782 +/- 1,120, respectively.

Analysis of Variance↗
PubMed1996

Schistosoma mansoni along Lake Albert, Kibale District, Western Uganda.

Four hundred and fifty one human strata living in the three fishing villages of Ndiaga, Kabukanga and Rwabikongoro along Lake Albert shore in Kibale District were examined for S. mansoni infection using Kato/Katz method. Of the 451 people, 409 (90.7%) were found infected with S. mansoni with geometric mean egg count of 561.3 eggs per gram (epg) faeces. Males had significantly higher mean egg counts than females, 608.3 epg and 415.6 epg respectively. All S. mansoni infected individuals were treated with praziquantel at 40 mg/kg body weight. Other common parasites observed were Asaris lumbricoides, Trichuris trichiura and hookworms. These were treated with mebendazole. Snail infection rate among the 115 Biomphalaria sudanica and the 56 B. stanleyi were 5.2% and 3.6% respectively. All the 66 Bulinus (B) tropicus found, were negative for cercariae shedding. The main pulmonate snails were 250 Lymnae natalensis, 500 Pila ovata and 375 Bellamya spp were the commonest prosobranchs followed by Bivalves (101).

Animals↗
PubMed1997

Change in schistosome sex ratio under the influence of a biotic environmental-related factor.

Schistosoma mansoni is a dioecious trematode responsible for intestinal schistosomiasis in man. The sex ratio was determined for S. mansoni adults derived from cercariae obtained from infected Biomphalaria glabrata maintained in the presence of the nonvector molluse. Marisa cornuarietis. The presence of M. cornuarietis is responsible for enhanced growth of B. glabrata and for a change in the sex ratio of the schistosome, which becomes more male-biased as compared to control snails maintained in aquaria lacking M. cornuarietis. This is the first time the presence of another species in the environment has been shown to influence schistosome sex ratios. Two nonexclusive hypotheses are proposed to explain this variation in the sex ratio: sexual competition between male and female sporocysts; and sex reversal.

Animals↗
PubMed1997

In vivo and ectopic encystment of Echinostoma revolutum and chemical excystation of the metacercariae.

In vivo and ectopic encystment of the cercariae of Echinostoma revolutum from Lymnaea elodes snails in Indiana and chemical excystation of the metacercariae were studied. In vivo encystment occurred in adults of Biomphalaria glabrata and Helisoma trivolvis (Colorado strain) snails and in neonatal and juvenile L. elodes snails. These results were expected because 37-collar-spined Echinostoma species show broad specificity in their second intermediate gastropod hosts. Encysted metacercariae of E. revolutum and Echinostoma trivolvis removed from experimentally infected snails and treated in a trypsin-bile salts excystation medium at 39 C showed 30.3% excystation for the former and 55.7% for the latter at 4 hr. The ducts and openings of the paraesophageal glands of excysted metacercariae of E. revolutum from cysts formed in snails did not stain with neutral red. Abnormal ectopic cysts with distorted outer walls and granular inner walls were obtained within 48 hr of placing E. revolutum cercariae in Locke's 1:1 plus 1% dextrose. These metacercariae excysted rapidly in the excystation medium and their paraesophageal gland ducts and openings stained with neutral red. Differences in ectopic encystment and chemical excystation in vitro can be used to distinguish these closely related species in the E. revolutum complex.

Animals↗
PubMed1997

Migration and development of mother sporocysts of Echinostoma caproni (Digenea: Echinostomatidae).

Experimental infections of the mollusc Biomphalaria pfeifferi by Echinostoma caproni miracidia (Mi) were carried out in order to analyze the migration and development of mother sporocysts (MS) at 26 C. Miracidia penetrated different parts of the host's body, such as the mantle collar, the foot and head covering (including velum and tentacles), the mantle cavity, and the oral cavity. The ventricle and common aorta were the final sites of infection for the mother sporocysts after migration. The path of migration of the sporocyst was influenced by the point of MS penetration, but in all cases the MS reached the ventricle through the venous system. Developmental studies showed that newly hatched Mi contained 5-7 germinal cells (the primary germinal cells) and some undifferentiated cells. During sporocyst development, every primary germinal cell apparently gave rise to a redial embryo, whereas undifferentiated cells gave rise to both somatic and secondary generative cells. The eventual degeneration of the sporocyst seemed to cause the end of the development of this germinal material. The MS produced about 15 mother rediae (MR). Intramolluscan development of E. caproni MS consisted of 5 main periods: (1) resting, (2) migration, (3) growth, (4) reproduction, and (5) degeneration. A lower temperature of 21 C affected the duration of each stage. However, the path of sporocyst migration, the pattern of their growth, and the developmental steps of the germinal material were similar.

Animals↗
PubMed1997

Partially degraded DNA of parasitological interest serves as an adequate template for the production of random amplified polymorphic DNAs (RAPDs).

Genomic DNA was extracted from Schistosoma mansoni adult worms and deliberately degraded by sonication. Samples with varying average molecular weight were subjected to RAPD (randomly amplified polymorphic DNA) analysis using the primer 3307 (5'-AGTGCTACGT-3') and other primers. Reproducible and complex DNA banding patterns were obtained, irrespective of the extent of DNA degradation. The same amplification protocol was employed with naturally degraded Biomphalaria glabrata genomic DNA and the primer 3302 (5'-CTGATGCTAC-3'). Again, reproducible RAPD patterns resulted. The experiment shows that the partially degraded DNA samples can be safely compared in RAPD analysis without artifactual bands compromising the accuracy of genetic analysis. Thus RAPD analysis permits complex and reproducible DNA fingerprinting from degraded samples of parasitological interest.

Animals↗
PubMedDate not supplied

[Factors responsible for cercarial concentration of schistosoma mansoni in Guadeloupe].

Research carried out in Guadeloupe on the sites of transmission of Schistosoma mansoni shows that the circadian evolution of the cercarial concentration (rhythm of presence) differs slightly according to the biotope:--in a running water habitat (greater than 0,10 m/s) the rhythm of presence is superimposed on the rhythm of emergence, which leads to a risk of contamination reaching a maximum between 11 a.m. and noon; --in a slow running water habitat (around 0,01 m/s), the acrophase of the rhythm of presence is clearly retarded in comparison with that of the rhythm of emergence. In this case, the risk of contamination is greatest between 2 p.m. and 5 p.m. because of the accumulation of cercariae. The absolute value of the cercarial concentration in running water results from two antagonistic processes: production of cercariae depending on the amount of Biomphalaria glabrata infected and dilution of cercariae depending on the flow rate of water. Thus along one channel the cercarial concentration shows great variation depending upon which of the above processes predominates. These results demonstrate that the risk of human contamination can never be directly deduced from the demography of vectors.

Animals↗
PubMed1998

Seasonal variation in molluscicidal activity of Solanum nigrum L.

Solanum nigrum L. leaves and fruits were shown to have molluscicidal activities against snails transmitting schistosomiasis and fascioliasis. In the present study, their molluscicidal activity against adult Biomphalaria alexandrina snails was assessed to determine whether plants collected at various seasons would have different degrees of toxicity. Leaves and fruits of three S. nigrum varieties were collected from Faiyoum and/or Giza during the four seasons. Leaves collected in autumn had the highest effect (LC50-35.4) followed by spring (LC50 = 44.36), summer (LC50 = 46.7) and winter (LC50 = 100.4). Toxicity of plant extracts was also affected by other seasonal dependent factors. These are the duration of plant exposure to direct sunlight and the size of the fruits. S. nigrum (black fruits) was more toxic (LC50 = 18.1) than the other two types, S. nigrum v. vellosum (yellow fruits) (LC50 = 38.9) and S. nigrum v. juidaicum (red fruits) (LC50 = 34.7).

Animals↗
PubMed2002

Molluscicidal and anti-feedant activities of diterpenes from Euphorbia paralias L.

Nine known diterpene polyesters of segetanes, jatrophenes and paralianes have been isolated from the aerial parts of Euphorbia paralias L. The molluscicidal activity of isolated compounds was evaluated on Biomphalaria alexandrina (Ehrenberg). Paraliane diterpene, (2S,3S,4R,5R,6R,8R,12S,13S,14R,15R)-5,8,14-triacetoxy-3-benzoyloxy-15- hydroxy-9-oxo-paraliane, was the most potent compound against the snail. Anti-feedant activity was tested by a conventional leaf disc method against third-instar larvae of Spodoptera littoralis (Boisd). Jatrophene diterpene, (2R,3R,4S,5R,7S,8R,13R,15R)-2,3,5,7,15-pentaacetoxy-8-angeloyloxy-14,15- dioxojatropha-6(17)-11E-diene, had the highest anti-feedant activity among the compounds tested.

Algorithms↗
PubMed1993

Phytochemical screening and molluscicidal potency of some Zairean medicinal plants.

A total number of 48 plants used in the Zairean pharmacopoeia were tested against molluscan intermediate hosts of schistosomiasis and fascioliasis. Aqueous and ethanolic extracts from five plants: Maesa lanceolata, Chenopodium ugandae, Asparagus racemosus, Phyllanthus nummulariifolius and Crinum zeylanicum, exhibited high mortality rate (100%) against Biomphalaria pfeifferi and Lymnaea natalensis. Their LC50 was respectively 0.1, 5, 5, 10 and 50 mg ml-1 for B. pfeifferi and 0.5, 5, 1, 10 and 10 mg ml-1 for L. natalensis. The activities are attributed to the presence of terpenoids, steroids and saponins in the plant extracts. Except for the extracts from Ch. ugandae however, the plants have shown toxic effect on fishes and aquatic insects.

Animals↗
PubMed2000

Biodegradability of the molluscicidal saponins of Phytolacca dodecandra.

The biodegradability of water-extracted saponins of berries from the Endod plant, Phytolacca dodecandra L'Herit, was evaluated under OECD standardized conditions. Persistence of the saponins was evaluated by determination of saponin concentrations in water over a 30-day period, using a quantitative HPLC method and a semiquantitative hemolytic assay, which is considered a potential field method. The two methods were compared. Bioassays were simultaneously conducted using Biomphalaria glabrata fresh water snails to assess the molluscicidal potency over time. All experiments were carried out in water, which was chemically balanced to sustain snails, and to one set river water was added to the medium to mimic natural conditions. (1) Saponin concentrations in water treated with an aqueous extract of P. dodecandra cultivar E44 were stable for 2 days then rapidly decreased during the third and fourth day. Lethal concentrations to snails were LC50 = 9.6 mg/l (95% CI: 6.3 to 19.4) in one set and LC50 = 6.8 mg/l (95% CI: 5.4 to 12.2) in the other. Adding river water to one set of the experiments had no effect on the mean saponin concentration over time (F = 0.02, P = >0.05). (2) Comparison of the hemolytic assay with the HPLC method showed no significant difference in mean saponin concentrations (t = 0.32, P > 0.05, 95% CI: -2.67 to 3.64), and a correlation of r2 = 0.88 between the two methods. (3) The saponin fraction of an aqueous extract of P. dodecandra was readily biodegraded (t1/2 = 15.8 h), and the complete consumption within a 10-day window indicates ready degradability in aquatic environments under aerobic conditions. (4) These results show that the use of Endod berries for snail control in schistosomiasis-infested water bodies is environmentally acceptable.

Animals↗
PubMed1982

Isoenzyme studies on cercariae from monoinfections and adult worms of Schistosoma mansoni (10 isolates) and S. rodhaini (one isolate) by horizontal polyacrylamide gel electrophoresis and staining of eight enzymes.

The enzyme phosphoglucose isomerase (PGI), phosphoglucomutase (PGM), hexokinase (HK), adenylate kinase (AK), fructokinase (FK), mannose-6-phosphate isomerase (MPI), glucose-6-phosphate dehydrogenase (G-6-PDH) and malate dehydrogenase (MDH) were chosen to study the variation between isolates, cercariae and adults, individuals, and sexes of Schistosoma mansoni and S. rodhaini, using horizontal polyacrylamide gel electrophoresis. The method described allows combinations of six of the eight enzymes to be scored in the homogenate from one adult worm. In adult S. mansoni one phenotype of the eight enzymes was observed in all isolates. In addition, the enzyme PGI showed polymorphism in the isolates from Tala, Kenya and Uganda. PGM in the isolates from Tala, Kenya and South Africa showed polymorphism. The cercarial phenotype differs from the adult phenotype in G-6-PDH, where the cercarial enzyme mobility is slower than that in the adult worm. The low amount of intrastrain variation observed in this species is explained by the limited amount of material used to establish the laboratory stocks, whereas the genetic similarity between geographically widely separated stocks does suggest that only limited geographical variation is likely to occur in S. mansoni. It is suggested that the gene controlling the PGI polymorphism is located on the sex chromosomes of S. mansoni. Mobility differences were observed between S. mansoni and S. rodhaini in the enzyme PGI and PGM, and these characteristics might be useful for a quick identification of schistosome cercariae emerging from Biomphalaria sp. in Africa.U

Adenylate Kinase↗
PubMed1991

Hemocyte production in trematode-infected Lymnaea truncatula.

In trematode-infected Lymnaea truncatula, as in other lymnaeids, hemocytes are formed in the connective tissue. Mitoses are found singly in blood vessels or connective tissue or occur in hemocyte nodules, developing along the mantle epithelium or associated with blood sinuses. The so-called hemocyte-producing organ in L. truncatula is not equivalent to that in Biomphalaria glabrata, but rather involves the proximal part of the kidney sac. It has a dual structure: the main part, containing podocytes and broad hemal spaces, is adapted for hemolymph filtration; the apical portion, adhering to the mantle and pericardial epithelia, has a thicker connective-tissue frame in which hemocyte nodules may develop. The role of this region of the kidney in hemocyte formation is discussed.

Animals↗
PubMed1994

Parthenogenesis in the genus Schistosoma: electrophoretic evidence for this reproduction system in S. japonicum and S. mansoni.

Mixed infections with Schistosoma japonicum and S. mansoni were carried out in mice. S. japonicum females paired with S. mansoni males developed normally and produced numerous viable eggs; very little sperm was found in the female genital tract. The eggs yielded many miracidia infective to Oncomelania hupensis, the host of S. japonicum. Cercariae arising from miracidia developed into male worms with an electrophoretic pattern of malate dehydrogenase (MDH) corresponding only to the maternal species S. japonicum. S. mansoni females paired with S. japonicum produced few viable eggs; sperm was found in the female genital tract. Miracidia hatched from some of these eggs were infective to Biomphalaria glabrata, the host of S. mansoni. Cercariae arising from miracidia developed into female worms with an electrophoretic pattern of MDH typical of the maternal species S. mansoni. It was concluded that S. japonicum females paired with S. japonicum males reproduce parthenogenetically. Parthenogenesis in schistosomes is discussed.

Animals↗
PubMed2003

Pharmacological and autoradiographical characterization of serotonin transporter-like activity in sporocysts of the human blood fluke, Schistosoma mansoni.

The present study focuses on the role of the biogenic monoamine serotonin (5-hydroxytryptamine) in the biology of sporocyst stages of the human blood fluke, Schistosoma mansoni, and its importance during obligate development within its snail host Biomphalaria glabrata. Based on previous work demonstrating that snails infected with S. mansoni have reduced levels of 5-hydroxytryptamine, we hypothesized that sporocysts actively transport this molecule from the host milieu. Intact sporocysts isolated in vitro take up exogenous 5-hydroxytryptamine via a high-affinity mechanism (K(m)=1.4 micromol l(-1)), and this serotonin transporter-like activity is dependent upon extracellular Na(+) and Cl(-) and is highly sensitive to previously characterized serotonin transporter inhibitors. Autoradiography suggests that transported [(3)H]5-hydroxytryptamine localizes within the body of the sporocyst, and in many cases is found in apical gland cells. Moreover, serotonin transporter-like activity is absent in free-swimming miracidia, the infective stage for the snail host, and the increase in larval serotonin transporter-like activity after miracidium-to-sporocyst transformation is accompanied by a corresponding decrease in steady-state levels of transcripts for tryptophan hydroxylase, the rate-limiting enzyme in serotonin biosynthesis. Overall our data suggest that S. mansoni larvae express surface-exposed serotonin transporter-like molecules, and that the transition from free-living miracidium to parasitic mother sporocyst is characterized by an increased dependence upon exogenous 5-hydroxytryptamine.

Animals↗
PubMed1996

Egg laying in vitro of Echinostoma caproni (Trematoda) in nutritive and nonnutritive media.

Egg laying in vitro was studied in Echinostoma caproni adults placed in 10 ml of nutritive or nonnutritive media for 48 h in petri-dish cultures maintained at 37 degrees C in an atmosphere containing 7.6% CO2. Maximal egg laying occurred within 24 h in the defined medium RPMI 1640. Egg laying was significantly greater in this medium than in McCoy's or Locke's solution. Eggs released into the RPMI medium were capable of producing miracidia that were infective to Biomphalaria glabrata snails. Fried and Huffman (1996) referred to a technique used to obtain eggs of Echinostoma caproni in the defined medium RPMI 1640, but details of the study were not given. No information is available on egg laying of echinostomes in vitro. Such information could contribute to a better understanding of egg release in digeneans and would also be helpful in the acquisition of eggs for biology and chemistry studies. Current techniques used to obtain echinostome eggs involve worm homogenization, teasing of eggs from the worms' uteri, or recovery of eggs from feces (see Idris and Fried 1996 for details). The purpose of this communication is to report on an efficient procedure for the acquisition of eggs of E. caproni after the placement of adult worms in the defined medium RPMI 1640. E. caproni adults were grown in ICR mice for either 17 (young worms) or 112 days (old worms) as described previously (Ursone and Fried 1995a). Worms were removed from the small intestines and rinsed rapidly in three changes of sterile Locke's solution containing penicillin (200 IU/ml) and streptomycin (200 micrograms/ml; Fried and Contos 1973). Worms were placed in culture media within 30 min of their removal from hosts. Nutritive media consisted of RPMI 1640 and McCoy's medium (Sigma, St. Louis, Mo.). Non-nutritive media consisted of Locke's or Locke's 1:1 (Ursone and Fried 1995b). All media contained antibiotics as described above.

Animals↗
PubMed2001

Differential display analysis of hemocytes from schistosome-resistant and schistosome-susceptible intermediate hosts.

Hemocytes from schistosome-resistant and schistosome-susceptible Biomphalaria glabrata differ fundamentally in their behavior towards an invading parasite. When the schistosome infects a resistant snail host it is quickly surrounded by hemocytes, encapsulated and destroyed. Hemocytes from susceptible hosts fail to kill the parasite. To detect the differences between these two host phenotypes, we used differential-display reverse-transcription PCR (DDRT-PCR), based on RNA extracted from isolated hemocytes. A number of differentially expressed fragments from resistant and susceptible snails were detected by DDRT-PCR and confirmed using single-strand conformation polymorphism. These methods proved to be sensitive enough to allow comparison and verification of differential gene expression in our system, where only small numbers of cells are available. The most interesting phenotype-specific fragments detected so far show sequence homologies to an adhesion molecule, defensin, serine/ threonine kinases, peroxidases and glycosidases.

Animals↗
PubMed2001

Biological aspects of a new isolate of Echinostoma paraensei (Trematoda: Echinostomatidae): susceptibility of sympatric snails and the natural vertebrate host.

A new isolate of Echinostoma paraensei (Lie & Basch, 1967) was obtained from a natural vertebrate host, the water rat Nectomys squamipes. Relationships with sympatric snails, Biomphalaria glabrata; Physa marmorata and Lymnaea columella, as well as allopatric snails and the definitive hosts N. squamipes, Mus musculus, Rattus norvegicus, Mesocricetus auratus and birds were investigated. E. paraensei developed in all sympatric snail species following exposure to one or five miracidia. P. marmorata showed the highest infection rate (34% and 36%) followed by L. columella (18% and 24%) and B. glabrata (8% and 28%), respectively. Mortality was elevated in the patent period, with L. columella having the highest values. B. glabrata, P. marmorata, and L. columella did not differ in relation to cercarial encystment, and metacercariae from each species were able to infect N. squamipes with similar worm burdens. Recovered adult worms were found in clusters from the first to third sections of the small intestine. Miracidia of E. paraensei hatched after 10 days incubation in darkness in dechlorinated water at 28+/-1 micro C. Miracidia began to hatch 1 h after exposure to incandescent light.

Animals↗