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The activities of aspartate aminotransferase (AST) (EC.2.6.1.1.) I, alanine aminotransferase (ALT) (EC.2.6.1.2) II and lactate dehydrogenase (LD) (EC.1.1.1.27) III have been measured in tissue homogenate and in haemolymph of Biomphalaria alexandrina snails, the specific intermediate host for the human parasitic disease schistosomiasis due to Schistosoma mansoni.
803 schoolchildren in the subprovince of Amran were examined for S. haematobium. The prevalence was 28.9%. Stool samples of 92 children were negative for S. mansoni eggs. Bulinus snails were most frequent, whereas Biomphalaria were rare. Control measures included chemotherapy and mollusciciding. The prevalence in 8 selected villages could be reduced by this from 36.3% down to 5.1%. No gross haematuria and only one single case of heavy infection were detected. Eradication of this disease seems feasible.
Total lipids were isolated from native and irradiated Biomphalaria alexandrina snails, specific intermediate hosts for Schistosoma mansoni.
Schistosomiasis caused by Schistosoma mansoni has not been reported in Baringo District of Rift Valley Province. The intermediate host (Biomphalaria species) though has been reported to occur along the shores of the lakes in this region. Three children from Baringo District were diagnosed to have schistosomiasis caused by S. mansoni by finding ova in their stools. They gave no history of visiting an endemic area. There are many dams being built for land reclamation, creating favourable conditions for the spread of the disease, in presence of the intermediate and definitive host. Studies on the current status of the disease and malacology should be undertaken in order to control the spread of the disease at an early stage.
Junctions between Sertoli cells, which form a continuous layer at the periphery of the 'acinus' in the ovotestis of Biomphalaria glabrata (mollusc gastropod), have been studied with conventional sections, lanthanum impregnation, replicas and scanning analysis of unstained sections. Extensive undulating septate junctions link Sertoli cells, which surround the various stages of spermatid differentiation. The morphology of the pleated septate junctions here presented indicates a possible role as a permeability barrier, which might result from the peculiar organization of the septa. The junctional complex is formed of areas where septa are parallel and regularly spaced, alternating with areas where septa separate and assemble with others, thus creating a complex system of channels, completely compatible with the sealing properties expected for these junctions. The morphology of septa, their possible anchorage within the membranes, and the interconnections linking the closely parallel septa are presented.
To study the feasibility of re-establishing a life cycle of Schistosoma mansoni (NMRI strain) from cryopreserved larvae, schistosomules were suspended in the cryoprotectant 1,2-ethanediol and cryopreserved in liquid nitrogen. Mice were injected intramuscularly with samples thawed after 3 days, 3 wk, or 6 mo in liquid nitrogen storage. Two to 5% of the cryopreserved larvae and approximately 18% of corresponding unfrozen control larvae developed into adult worms. Infectivity did not decrease as a function of storage time. The adult worms showed no structural damage or changes in overall size and morphology when examined by light and transmission electron microscopy. Female worms derived from cryopreserved larvae had the same or slightly elevated egg production as controls, but tissue egg distributions were comparable. Subsequent passages through Biomphalaria glabrata snails and mice revealed no difference in snail prepatent death rate, percentage of snails infected, cercarial production per snail, or cercarial infectivity.
It has been demonstrated that the infectivity of Schistosoma mansoni miracidia for a highly susceptible strain of Biomphalaria glabrata was reduced markedly when the miracidia were pretreated with hemolymph from the snail Helisoma caribaeum. Although the Helisoma hemolymph factor(s) responsible for this phenomenon has not been identified with certainty, it appears to be a snail lectin associated with binding sites for n-acetyl-D-glucosamine on the surface of the miracidium. Hemolymph from uninfected and infected B. glabrata and from a resistant strain of B. glabrata did not reduce the infectivity of miracidia, nor did pretreatment with bovine plasma albumin. Likewise, we demonstrated that reduction of miracidial infectivity was not due to the presence of a miracidial immobilizing factor found in the hemolymph of many snail species. Differences in the infectivity between pretreated miracidia and controls were statistically significant (P = 0.001).
The molluscicidal activity of crushed seed pods of Swartzia madagascariensis was assessed by laboratory and field trials. Mature dry seed pods were ground and extracted in tap water for 24 h. Water extracts exerted a significant molluscicidal activity against Bulinus globosus up to dilutions of 100 mg of ground pods per litre. The chromatographically isolated saponin (1) responsible for the molluscicidal activity showed a toxicity of LC 100 at 3 mg/l after exposure of B. globosus and Biomphalaria glabrata for 24 h. Saponin (1) could be identified by FAB-MS and 13C-NMR-spectroscopy as oleanolic acid-3-O-beta-D-glucuronopyranosyl (1----3)-alpha-L-rhamnopyranoside. Two field trials with S. madagascariensis pod extracts in ponds (60 and 160 m3) harbouring dense populations of B. globosus compared well with the laboratory findings and showed the efficiency of the molluscicide in a natural habitat. A single application of the plant molluscicide significantly reduced the populations of B. globusus. The toxicity of S. madagascariensis pod extracts to non-target organisms remains an obstacle for its use in certain situations where schistosomiasis control is envisaged and where S. madagascariensis is found. However, S. madagascariensis is a valid candidate molluscicide which may be applied in selected epidemiological settings as part of integrated schistosomiasis control measures.
The pattern of fluctuation in the population size of Bulinus globosus and Biomphalaria pfeifferi, in their infection rates with Schistosoma haematobium/S. mattheei and S. mansoni, respectively, and in the cercarial population size as monitored using hamster immersions, was elucidated in streams in the temperate highveld region of Zimbabwe over a 27-month period during 1982-1984. The results revealed that transmission of S. mansoni was erratic and unpredictable without a clearcut seasonal transmission pattern. In contrast, transmission of S. haematobium and S. mattheei exhibited a marked seasonal pattern, being most intensive during the hot, dry season (September-November) and markedly reduced during the cold, dry season (June-August). During the rainy (December-February) and warm, post-rainy (March-May) seasons transmission was moderate and variable, but occasionally intensive. The results also showed that rodent immersion is to be preferred to measurements of snail population size and snail infection rate in elucidating seasonality of transmission of schistosomiasis.
The size and number of colonies of Biomphalaria glabrata were reduced after four years of a surveillance/treatment snail control programme using an emulsifiable concentrate of niclosamide (25% active ingredient). Surveys among the human population showed that the incidence of new Schistosoma mansoni infections in 0-10 year-old children fell from 22% to 4.3%, while in a comparison area the incidence remained at 20%. With reduced transmission over four years, the prevalence of infection in a cohort of children examined in 1971 and 1975 fell from 34% to 23%. The fall in prevalence and intensity of infection led to a reduction of 66% in the index of potential contamination, which was reflected in a reduced rate of infection among sentinel snails and representative samples of B. glabrata collected during surveillance searches.The overall annual cost of the programme was US $3.24 per capita.
The discovery of Biomphalaria pfeifferi, the intermediate host of Schistosoma mansoni, in the RSA in the recreational area of Lichtenburg prompted an investigation to assess the bilharzia risk posed by their presence. Localized populations of B. pfeifferi were found in the recreational area and in the adjoining game breeding farm. The population of downstream areas by the snails appears to be prevented by the water quality. It is proposed that the large populations of aquatic birds in the game breeding farm be lured to the snail-infested areas as a possible means of eradication. The susceptibility of these snails to S. mansoni was experimentally confirmed.
At the moment, it seems unlikely that there is a possibility for schistosomiasis implantation in French Guiana. The reasons to this are both the number of the immigrants infested by Schistosoma mansoni which is quite low and the disappearance of the intermediate host Biomphalaria glabrata. The disappearance of the species may be a temporary one.
The prevalence and intensity of infection with Schistosoma mansoni were determined in a sample of the population of the city of Higuey, Dominican Republic. The quantitative formol-ether stool sedimentation technique of Ritchie, as modified by Knight et al., was performed on stools from 1,025 (65.5%) of 1,563 individuals greater than 1 year old. The highest prevalence rates (21.4%) were observed in women 25-29 years old and in men 15-19 years old (20%). The maximum fecal egg count was in the 15- to 19-year age group, with a geometric mean of 30 eggs/g feces among men and 15.8 eggs/g feces in men and women. The overall prevalence of S. mansoni-infection was 11.8% with a geometric mean excretion of 8.8 eggs/g feces. In addition, the circumoval precipitin test was carried out on 639 sera and 110 (17.2%) were positive, increasing the prevalence in all age groups. Examination of Biomphalaria glabrata snails collected in early 1986 showed 7.8% to be positive for S. mansoni cercariae. Despite the moderate prevalence rates and the low intensity of infection among the human population, we consider Higuey to be an important focus of schistosomiasis in the Dominican Republic. The sensitive coprological and serodiagnostic techniques we employed have helped to identify the age- and sex-specific groups most deserving of treatment in order to reduce transmission of infection and disease prevalence.
Five male and 5 female clones of Schistosoma mansoni were established and maintained for 3 yr by the serial microsurgical transplantation of sporocysts from infected to uninfected Biomphalaria glabrata snails. The clones were initially derived from 10 randomly selected snails with monomiracidial infections. Clones were characterized by several criteria, including their infectivities for mice and snails, their cercarial outputs, and their ability to produce immunity in mice. The mean infectivities of individual clones in mice ranged from 26 to 44%, and were highly consistent within each clone. The infectivities of cloned sporocysts in snails ranged from 44 to 100% and were also highly consistent within clones. Mean cercarial outputs from individual clones ranged from 450 to 4,300 per snail. In mice, clones differed significantly from each other in their ability to immunize and in their susceptibility to immunity. Each clone was unique and did not appear to differ with time or subpassaging through snails, suggesting that the differences had a genetic basis.
With the starting point in a comprehensive and integrated longitudinal study conducted by the Blair Research Laboratory from March 1982 to May 1984 in Bushu and Chiweshe communal areas, a review is presented of the dynamics of transmission of urinary (Schistosoma haematobium) and intestinal (S. mansoni) human schistosomiasis in the highveld region of Zimbabwe. The study comprised observations on snail-related aspects of transmission, on human water contact patterns, and on prevalence, intensity and incidence of infection in the human definitive host population. S. haematobium was found to be of high endemicity whereas the endemicity of S. mansoni was moderate. This reflects that Bulinus globosus, the snail host for S. haematobium, is better adapted to the biologically unstable freshwater environments than Biomphalaria pfeifferi, the snail host for S. mansoni. The most essential findings comprise a marked seasonality and focality of transmission, an overdispersed distribution of infection, individual predisposition to infection, peak of prevalence and intensity of infection among children and young adults, a positive correlation between infection status in population subgroup and the relative transmission potential of water contact sites used, a pronounced specificity and marked conservatism in the human water contact pattern. The epidemiological background for schistosomiasis control strategies is outlined, and a community-based strategy within the primary health care system for schistosomiasis morbidity control is described. The community-based primary health care approach to schistosomiasis morbidity control is the strategy adopted in Zimbabwe.
After-effects of hybridization of S. mansoni strains, having Biomphalaria pfeifferi as an intermediate host, have been revealed for the first time. The crossing of two african strains (malarial-M and guinea-G), which have different compatibility rates with their specific intermediate hosts, has shown that hybrids display a higher virulence in respect to molluscs-hosts than maternal strains. The compatibility rate of the first generation hybrids with B. pfeifferi decreased, the breachs in the compatibility being the more significant the higher the degree of adaptation between the maternal strain and specific intermediate host. The infectiousness of the second generation hybrids in respect to molluscs of two populations of B. pfeifferi (M and G) virtually did not differ and varied in the ranges of mean values between the initial infectiousness of two maternal strains.
Circulating hemocytes of the snail, Biomphalaria glabrata, synthesize and secrete a variety of polypeptides when maintained in vitro in serum-free medium containing [35S] methionine. SDS-PAGE/fluorographic analysis of supernatants from resistant snail (10-R2-OK strain) hemocyte cultures revealed the presence of numerous labeled polypeptides ranging in Mr from 220 to 14 kDa. Most of these same proteins were also produced by hemocytes of a susceptible B. glabrata strain (M-line), but the overall rate of secretory protein synthesis was reduced from that of resistant snail cells. In addition, excretory-secretory (ES) products contained in supernatants from Schistosoma mansoni miracidial transformation and 1-day primary sporocyst cultures stimulated increases in the synthesis of various polypeptides. Particularly striking was a 3-fold increase in the synthesis of a 66-kDa secretory polypeptide by hemocytes of both snail strains, and a concomitant increase in M-line hemocytes and decrease in 10-R2-OK cells of a 63-kDa polypeptide. Overall, however, the level of ES product-induced secretory protein synthesis was greater in 10-R2-OK snail hemocytes than in those of the M-line strain. Exposure of a nonhemocytic B. glabrata cell line to parasite culture supernatants had no stimulatory/inhibitory effect on labeled protein ouput, suggesting that the observed hemocyte response may be snail cell-type specific. Finally, the larval ES components responsible for modulating hemocyte protein metabolism are mainly concentrated in a heat-stable fraction composed of molecules of greater than 30 kDa. However, the loss of the ability of heated parasite products to stimulate synthesis of certain hemocyte proteins and the presence of minor stimulating activity in a low molecular weight fraction (less than 10 kDa) implies the possible existence of multiple larval components affecting formation of specific hemocyte secretory polypeptides. It is concluded that snail hemocytes are capable of in vitro synthesis and secretion of a variety of methionine-containing polypeptides, and that ES products of early larval schistosomes can modulate (i.e., stimulate or inhibit) this metabolic process. A differential response of susceptible vs. resistant hemocytes to larval products suggests that the degree to which these cells can be metabolically activated may determine their cytotoxic effectiveness.
Fifty local medicinal, agricultural and wild growing deciduous plants, representing 49 species, 46 genera and 22 families, were screened as water extracts at 1:1000 concentration for molluscicidal activity against Biomphalaria pfeifferi in Machakos District, Kenya. Forty-seven of the 50 (94%) plants and 106 of the 134 (79%) plant materials (roots, stems, leaves, fruits, flowers and seeds) were molluscicidal. The leaves of Pappea capensis (Sapindaceae), Steganotaenia araliacea (Umbelliferae), Zornia setosa subsp. obvata (Papilionaceae) and Terminalia kilimandscharica (Combretaceae), the flower pods of Hyptis pectinata (Labiatae), the seeds of Acacia nilotica (Mimosaceae) and the fruits and roots of Solanum nigrum (Solanaceae) gave 100% kill. Another 15 species produced mortality rates between 53% and 87%. Plants were evaluated for possible use in local snail control programmes by considering their growing characteristics, habitat requirements, toxicity in non-target organisms, abundance in the study area and competing uses.