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PubMed2002

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.

Animals↗
PubMed2003

First report of a natural hybrid between Schistosoma mansoni and S. rodhaini.

Experimental crosses between Schistosoma mansoni and S. rodhaini have shown that hybrid offspring are viable, yet, until now, no naturally occurring hybrid has been identified. A collection of freshwater snails from Nyamlebi-Ngoma, Ukerewe Island, Lake Victoria, Tanzania, yielded a mixed infection within a single Biomphalaria sudanica of S. mansoni females and S. mansoni-S. rodhaini hybrid males. The hybrids were identified using deoxyribonucleic acid (DNA) sequences. Mitochondrial DNA 16S and 12S sequences of the hybrids match those of S. mansoni, whereas their nuclear ribosomal DNA ITS1 and ITS2 sequences match those of S. rodhaini. The identification of hybrids in Tanzania highlights the possibility that the genetic identity of either parasite species might be modified by introgression.

Animals↗
PubMed2005

Age of adult worms of Echinostoma caproni does not affect development of miracidia.

The effect of the age of adult Echinostoma caproni on egg development was studied. The percentage of fully developed miracidia was determined in eggs derived from adult worms obtained from laboratory mice at 2, 4, 6, and 8 wk postinfection (PI). Regardless of the age of worms from which the eggs were obtained, the percentage of fully developed miracidia was always >90%, and 60-80% of the eggs hatched. Several previous studies have shown that eggs derived from 2- to 4-wk-old E. caproni yielded miracidia that infected Biomphalaria glabrata snails. Results of the present study on E. caproni were in marked contrast to previous results with Echinostoma friedi, for which viable eggs were not obtained at 2 and 3 wk PI and maximal infectivity of miracidia in snails was obtained from eggs derived from worms collected at 8 and 9 wk PI. Further studies are needed to determine if the egg viability of other species in the "revolutum" group follow that of E. caproni or E. friedi.

Animals↗
PubMed2004

Susceptibility of 7 freshwater gastropod species in Zimbabwe to infection with Gastrodiscus aegyptiacus (Cobbold, 1876) Looss, 1896.

Gastrodiscosis outbreaks due to Gastrodiscus aegyptiacus were recorded in horses in the vicinity of Harare, Zimbabwe, in the absence of Bulinus forskalii, B. senegalensis and Cleopatra sp. which are considered to be the only intermediate host snails. This suggested the possibility of other snail species acting as intermediate hosts in the life cycle of the trematode. A study was carried out to determine the susceptibility of 7 freshwater snail species to infection with G. aegyptiacus. First generation (F-1) of 5 freshwater pulmonate snail species, Bulinus tropicus, Bulinus globosus, Biomphalaria pfeifferi, Helisoma dyuri and Physa acuta that were bred in the laboratory, and 2 prosobranch snail species, Melanoides tuberculata and Cleopatra sp. that were collected from the field were used in this study. Data pertaining to mortalities and cercariae shedding were recorded throughout the experimental period. The prosobranch snails, M. tuberculata and Cleopatra sp. were susceptible to G. aegyptiacus with a minimum prepatent period of 45 days and 54 days, respectively. Bulinus tropicus, P. acuta and H. duryi were susceptible as evidenced by the presence of different generations of rediae and mature cercariae on dissection at 59 days post-infection although attempts to induce the snails to shed from 28 days post-infection did not produce cercariae. Bulinus globosus and Bio. pfeifferi were refractory to infection. The results revealed the ability of G. aegyptiacus to infect M. tuberculata, Cleopatara sp., B. tropicus, P. acuta and H. duryi under experimental conditions and this may explain the recorded outbreaks of gastrodiscosis in equine populations in Zimbabwe in the absence of the known intermediate hosts. Bulinus tropicus is considered as the most likely major intermediate host of G. aegyptiacus because of its wide distribution in Zimbabwe and is well adapted to a wide variety of environments.

Animals↗
PubMed1976

Studies on schistosomiasis in Saudi Arabia.

During studies on schistosomiasis in Saudi Arabia, urine and stool samples from inhabitants of various areas (mostly rural) were examined, and 97 aquatic habitats in 46 localities were searched for snails. The results indicate the occurrence of both urinary and intestinal schistosomiasis in most parts of the country, with a patchy distribution and varying infection rates. The snail intermediate host of Schistosoma mansoni was found to be Biomphalaria arabica. For S. haematobium three species of snails, namely, Bulinus truncatus and B. beccarii in the west and B. reticulatus wrighti in the northeast, may transmit the infection; the susceptibility of the two former species has been confirmed in the laboratory. The limitation in the size of snail habitats--which consist of wells, small canals, cisterns, small swamps, interrupted streams, and ponds--creates a special type of transmission which can be defined as "oasis transmission," making control of the disease both simple and practical.

Adolescent↗
PubMed1977

Control of Schistosoma mansoni transmission by chemotherapy in St. Lucia. II. Biological results.

Chemotherapy of all persons infected with Schistosoma mansoni was begun in Marquis Valley, St. Lucia, in March 1974. From January 1972 to the start of chemotherapy, the infection rate in field Biomphalaria glabrata collected in the valley was 1.09% (117/10,736) and the rate in sentinel B. glabrata was 1.48% (56/3,790). From March 1974 through December 1975, no infections were detected in either field snails (11,742 collected) or sentinel snails (3,230 exposed). The accumulated date suggest that, because of differences in topography and average annual rainfall, S. mansoni transmission occurs in this valley during the rainy season, whereas in other St. Lucian valleys under study it occurs during the dry season.

Animals↗
PubMed1978

Laboratory and field trials of a slow-release copper molluscicide in St. Lucia.

Tests of a slow-release molluscicide containing 50% copper sulfate were under-taken in laboratory and field situations in St. Lucia. In laboratory trials, a granule form of the molluscicide produced 100% mortality of Biomphalaria glabrata down to 4 mg/liter active ingredient (a.i), while the pellet form produced 100% mortality down to 8 mg/liter a.i. In field trials, a dose of 100 mg/liter a.i. in granule form caused mortality of B. glabrata in banana drains but had no effect on B. glabrata populations in a marsh habitat. In both habitats, the dose of 100 mg/liter produced mortality of other molluscan fauna which caused changes in the molluscan diversity indices. This failure in field trials may have been due to dilution of copper levels caused by flooding and also by uptake of copper by mud and algae.

Animals↗
PubMed1979

Schistosomiasis in Omo National Park of southwest Ethiopia.

Schistosomiasis mansoni infection was found in more than 50 tourists who had visited Omo National Park, Ethiopia, and bathed and swum in the Mui River. A survey revealed Schistosoma mansoni infection in 41% of Park residents and in 33% of the neighboring Suri people. Eggs were found in stools and adult worms at autopsy of wild Papio anubis and Cercopithecus aethiops. Trematode larvae were found in 27% of Biomphalaria pfeifferi snails found in the Mui River. The source of the disease and the implications of its spread with the future development of the Omo Valley are discussed.

Adolescent↗
PubMed1979

A longitudinal study of schistosome vector snail populations in Liberia.

Seasonal changes in populations of Biomphalaria pfeifferi and Bulinus globosus were observed at 62 locations in Liberia, West Africa. All varieties of water in both urban and rural locations were sampled. A wet season decrease and dry season increase of B. globosus populations in both urban and rural locations, similar to that reported elsewhere in West Africa, was observed. Similar fluctuations of B. pfeifferi populations were noted. The prevalence of schistosome infected vector snails varied markedly between rural and urban locations. At rural sites parasite prevalence followed the appropriate vector snail prevalence. At urban sites a portion of the vector snail population appeared relatively unaffected by seasonal changes. This stable population harbors a reservoir of infected snails that sustain year round transmission. Human infection was sampled in school children in the study area and prevalence of approximately 50% was found for both Schistosoma mansoni and S. haematobium. Added to the malacologic information this suggests less than hyperendemic transmission. The data suggest that urban environments should receive priorities for control programs.

Animals↗
PubMed1980

The Boqueron Project after 5 years: a prospective community-based study of infection with Schistosoma mansoni in Puerto Rico.

The Boqueron Schistosomiasis Project is a prospective community-based study of Schistosoma mansoni infection after the interruption of transmission by nonchemotherapeutic control measures. The study methods and the parasitologic results of the first five annual stool surveys are described in this report. In the first year, 1972, among 904 inhabitants (88% of the total population) the prevalence of infection was 40%, and the geometric mean intensity of infection among positives was 16.1 eggs per gram (epg). Snail control was begun in early 1973 with molluscicides and habitat modification. Intensive monitoring every 2 weeks revealed only 63 noninfected Biomphalaria glabrata in the community during the subsequent 4 years. The incidence of new infectins among people negative in all previous surveys dropped from 17% in 1972 to 1% in 1974 and has remained negligible since then. Among young children and newborn, only four new infections (all less than 5 epg) were found after the first control year. Despite this low rate of transmission, prevalence only decreased from 37% to 34%, and the population geometric mean fecal egg output has not substantially changed in a cohort of 528 individuals examined in each of the six annual surveys. Possible reasons for the minimal change in parasitologic status are discussed and include water contact behavior outside the community and changes in laboratory techniques. Data from the first 5 years of the study suggest that in a population where mean intensity of infection with S. mansoni is low, further decreases in prevalence and intensity of infection occur slowly. The implications for control programs based on nonchemotherapeutic measures are discussed.

Adolescent↗
PubMed1982

Evaluation of chemotherapy in the control of Schistosoma mansoni in Marquis Valley, Saint Lucia. II. Biological results.

Following the final chemotherapy campaign of a 4-year program, the biological assessment of transmission of Schistosoma mansoni was evaluated for 5 years. No infected Biomphalaria glabrata were found amongst 28,791 and 13,550 snails examined from flowing and static index sites, respectively. However, 89 infected snails of 16,602 examined (0.54%) were found from additional sites. Sentinel snails examined between March 1974 and October 1977 revealed no infections and their use was discontinued. Following an increase in transmission, routine focal mollusciciding at 4-weekly intervals was introduced in March 1980. The cost for eight applications was US $641, representing a cost per caput of $0.21. These figures, extrapolated to a full year's control, become $1,042 and $0.35, respectively. The maximum cost was for the molluscicide, which absorbed 71.5% of the total. The data suggest that the main transmission of S. mansoni occurs in the dry season, in flowing habitats, as it does elsewhere in St. Lucia.

Animals↗
PubMed1983

Studies on schistosomiasis in Taiz Province, Yemen Arab Republic.

Infection with both urinary and intestinal schistosomiasis is prevalent with patchy distribution in Taiz Province, southwest Yemen Arab Republic. Schistosoma haematobium with a prevalence as high as 90% was found in the western, southern, and northern parts of the province. Among school children the overall prevalence was 37%. Infection rates did not differ significantly among various age and sex groups. Three species of Bulinus--B. beccarii, B. truncatus, and B. wrighti--have been found in the province, B. beccarii having the widest distribution and highest density. S. mansoni was found in most parts of the province. A 100% prevalence was found in some schools. The overall prevalence was 64% among school children and 68% among inhabitants of villages surveyed. Highest prevalence was found in the age group 10-20 years. Hepatosplenomegaly was prevalent among children in highly endemic areas. Biomphalaria pfeifferi, the intermediate host of S. mansoni, was found in most valleys.

Adolescent↗
PubMed1990

Human schistosomiasis in Cameroon. II. Distribution of the snail hosts.

A nationwide survey for snail hosts of human schistosomes was carried out in Cameroon between 1985 and 1988. In total, 668 sites at 432 locations were sampled. In the arid, northern half of the country (tropical climatic zone), where both intestinal and urinary schistosomiasis are hyperendemic, Biomphalaria pfeifferi was the only Schistosoma mansoni host and Bulinus globusus and B. senegalensis the most common S. haematobium hosts. In that region, these snails occurred almost exclusively in temporary bodies of water. Taking into account results from a companion study on the distribution of schistosomiasis in humans, our results clearly show that temporary water bodies in the tropical zone are the principal foci of transmission. These findings disagree with commonly held views about schistosome transmission in Cameroon. B. truncatus, a S. haematobium host, was also present in the tropical zone but was found principally in perennial habitats. Although some perennial habitats were important transmission sites, they represent only a small portion of the overall problem. B. truncatus is the principal S. haematobium host in the wetter southern half of the country where schistosomiasis haematobium is highly focal. Biom. camerunensis was far more common than Biom. pfeifferi in the South but did not occur where S. mansoni prevalence rates were high; thus it appears to be a poor host. B. forskalii, the sole host of S. intercalatum in Cameroon, occurs widely throughout the country; however, the schistosome is restricted to a small region in the South.

Animals↗
PubMed1991

Control of schistosome-transmitting snails in Kenya by the North American crayfish Procambarus clarkii.

Snail-transmitted trematode parasites such as schistosomes and liver flukes assume considerable medical and veterinary significance in tropical Africa. We have observed a strong negative association between the presence of medically important pulmonate snails and the crayfish Procambarus clarkii in freshwater habitats in Kenya. This crayfish, introduced into Kenya around 1970, readily consumes these snails in the laboratory. Field enclosure experiments indicate that crayfish exert a significant negative impact on the abundance of Biomphalaria pfeifferi, the intermediate host of the human blood fluke Schistosoma mansoni. It is likely that P. clarkii will continue to spread naturally in Kenya and that schistosome-transmitting snails will be excluded or reduced in numbers where crayfish are present. Procambarus clarkii may represent an alternative, biological means of snail control in East Africa.

Animals↗
PubMed2000

A preliminary assessment of the potential of the Muschovy duck (Cairina maschata) as a biocontrol agent of schistosomiasis intermediate host snails.

OBJECTIVE: To assess the impact of Muschovy ducks on snail populations. DESIGN: Populations of four different snail species were monitored in nine ponds for a period of 32 weeks. Zero, one and two ducks were randomly introduced to a set of three ponds in the 16th, 20th and 24th week. SETTING: Nine fenced ponds at De Beers Research Laboratory, Chiredzi. MAIN OUTCOME MEASURES: Reduction in snail population following introduction of ducks. RESULTS: Mean counts for the intervention period showed that more intermediate host snails (Bulinus globosus and Biomphalaria pfeifferi) were present in ponds where ducks were not introduced (control) than in ponds where either one or two ducks were introduced. In control ponds the mean counts for intermediate host snails were 1.37, 1.03 and 1.02 for control, treatment with one duck and treatment with two ducks respectively. Similar observations were made for Physa acuta, with mean counts of 1.10, 0.64 and 0.67 for control, treatment with one duck and treatment with two ducks, respectively. No differences were observed in snail counts of Melanoides turbeculata where 2.40 snails were collected from the control pond and 2.37 snails in both treatment ponds. There was no significant difference in number of snails in ponds with one or two ducks. CONCLUSION: The study demonstrated that Muschovy ducks significantly reduce snail populations in a pond environment. Further studies are required in large natural ponds before conclusive recommendations are made on the use of Muschovy ducks as biological control agents of schistosomiasis intermediate host snails can be drawn.

Animals↗
PubMedDate not supplied

[French Guiana and bilharziasis].

The authors discuss about the lack of bilharziasis in French Guyana and report the experimental infestation of Biomphalaria glabrata coming from Cayenne with a porto-rican strain of Schistosoma mansoni.

Biomphalaria↗
PubMed1999

[Intestinal schistosomiasis from Schistosoma mansoni in Madagascar: extent and center of the endemic].

Schistosoma mansoni and S. haematobium affect respectively 2 million and 500,000 persons in Madagascar. Over the past decade, S. mansoni has spread in the central Highlands of Madagascar, essentially throughout the mid-west and Antananarivo plain. To understand this recent change in the epidemiology of S. mansoni, we examined the relationship between its spatial distribution and several host factors, including labour migration, urbanization and water development projects. In the Highlands, the disease in distribution could be superimposed on the potential expansion areas of snail distribution defined in 1958. However, the distribution is not homogeneous, as for example the road between Betafo and Mandoto (South West of Antananarivo). This focal pattern described in other African countries is unique to the central Highlands of Madagascar. Rice cultivation is the main economic activity and is associated with intense water contact. The focal distribution may be related to an environmental adaptation of host-parasite interaction depending on behavioural patterns, water and soil chemistry and incompatibility between Biomphalaria pfeifferi and S. mansoni. It is also possible that these focal patterns precede homogeneous endemicity, as along the road Itasy-Tsiroanomandidy (west Antananarivo). Major water development carried out in this migration area led to a rapid endemization of the disease. In Befato-Mandoto, where soil management is more restricted, schistosomiasis due to S. mansoni seems to have been established in some foci where epidemiologic conditions are favourable (for example, traditional irrigation canals). In contrast, the spread of S. mansoni in the Antananarivo plain closely follows the settlement of an infected rural population. Epidemiologic surveys conducted on school children in the Antananarivo suburbs, where sanitary conditions are poor, showed a prevalence of 25%. Human migration linked to development projects and urbanization seems to be the principal factor associated with the spread of schistosomiasis in the mid-west area and Antananarivo plain. In the Highlands, the preferential exposure of adult labour migrants has contributed to the widening of the endemic area.

Adult↗