Field studies on the transmission of Schistosoma mansoni and on the bionomics of its intermediate host, Biomphalaria glabrata, on St. Lucia, West Indies

Schistosoma mansoni is transmitted by the snail Biomphalaria glabrata on the West Indian island of St. Lucia. A 2$\text{1}\text{2}$-year study of natural snail populations is reported together with simultaneous observations on the transmission of the parasite. Populations in static habitats (pools, marshes and lateral banana drains) were maximal during the rainy part of the year (June–December) but declined during dry spells between January and May. Low infection rates (< 1 %) were observed sporadically in these populations. Higher, more persistent infection rates (5–15%) were obtained in flowing habitat populations (streams and main banana drains) which, however, only became established in periods of low rainfall. The importance of seasonal transmission through flowing habitat colonies was borne out by mouse exposures, supplementary snail studies and human incidence data which between them also gave an insight into the dynamics of transmission. These findings have been used to design a mollusciciding programme as one of several methods of controlling transmission currently being evaluated on St. Lucia.     

Snail findings from an experimental mollusciciding programme to control Schistosoma mansoni transmission on St. Lucia

An experimental molluscicide programme to minimize Schistosoma mansoni transmission has been in operation in a valley on the West Indian island of St. Lucia since September, 1970. Areas infested with the snail Biomphalaria glabrata received an initial intensive treatment. A fortnightly surveillance-treatment programme, with focal mollusciciding of any living snail colonies detected, was then developed. Snails were eliminated from some static habitats but the majority required repeated focal treatments to keep their snail colonies small and localized with low infection rates. No stream colonies were detected in the 1972 and 1973 dry seasons, although such colonies became established in other valleys. The belief that eliminating the stream colonies should have reduced S. mansoni transmission is supported by the apparent absence of cercariae in certain streams and by preliminary medical findings. A detailed cost analysis is included. Based on this experimental programme, a cheaper programme is outlined which should be suitable for use by public health authorities.     

Biological characteristics and control of intermediate snail host of Schistosoma japonicum

Except for imported cases, we have had no new Schistosoma japonicum infection in Japan since 1977. But there are still two habitats of the intermediate snail host: Oncomelania nosophora in the previous endemic areas of Kofu Basin and Obitsu. O. nosophora from Kofu Basin and Obitsu are susceptible to Chinese and Philippine strains of S. japonicum. The number of immigrants from current endemic areas in China or the Philippines is increasing. In order to prevent re-emerging of S. japonicum infections in Japan, we should continue monitoring on those existing snail hosts and investigate an adequate quarantine system. In Japan, elimination of schistosomiasis has been mainly accomplished by control of the snail host. As measures of snail control, cement-lining of ditches and chemical mollusciciding were most effective in Japan. But the cost of this joint program is too expensive compared with health budget in almost developing countries. In endemic areas of Japan, land reformation from paddy field to fruit farm was also effective. The intermediate snail host in the Philippines, Oncomelania quadrasi is much more aquatic than O. nosophora. For control of O. quadrasi, small drainage of the water and land reclamation from swampy field to rice-field were effective. Based on biological characteristics of Oncomelania spp., we can modify the past successful snail control program in Japan to be adapted ecologically and economically to each endemic area of developing countries.     

Capacity of irradiated echinostome sporocysts to protect Schistosoma mansoni in resistant Biomphalaria glabrata

Three closely related species of Echinostoma flukes each has a distinctive pattern of protection of Schistosoma mansoni in schistosome-resistant Biomphalaria glabrata host snails. Protection of developing S. mansoni by irradiated E. paraensei sporocysts in the schistosome-resistant snail host was strong; protection induced by irradiated E. lindoense and E. liei sporocysts was weak or not measurable. The capacity of irradiated E. paraensei sporocysts to interfere with the host's innate anti-schistosome response also differed between strains of B. glabrata. Protection of S. mansoni strain Lc-1 was greater in B. glabrata strain 10-R2 than it was in strain M-RLc snails. Irradiated E. paraensei sporocysts also induced a different response to the two schistosome strains in a single host strain. Irradiated E. paraensei sporocysts induced in B. glabrata 10-R2 snails a stronger protection of S. mansoni strain PR-1 than of strain Lc-1. Exposure of each snail to the irradiated E. paraensei miracidia usually protected the following challenge schistosome infection better when 30 rather than 10 irradiated echinostome miracidia were used.     

Cloning and partial nucleotide sequence of Schistosoma japonicum paramyosin: a potential vaccine candidate against schistosomiasis.

, , , and 1992. Cloning and partial nucleotide sequence of Schistosoma japonicum paramyosin: a potential vaccine candidate against schistosomiasis. International Journal for Parasitology 22: 1187–1191. Paramyosin from the blood fluke, Schistosoma mansoni, has shown promise as a vaccine candidate for schistosomiasis mansoni. Here we report the cloning and partial nucleotide sequence of a cDNA encoding paramyosin from the related human parasite, Schistosoma japonicum. Affinity purified antibodies to this clone recognized a S. japonicum antigen of molecular weight 97 kDa, equivalent to the reported size of S. mansoni paramyosin. Alignment of the cDNA sequence with that of S. mansoni paramyosin revealed 90% identity. Comparison of the predicted amino acid sequences revealed 95% identity. Although these two parasites differ in many characteristics, the substantial homology demonstrated here between S. mansoni and S. japonicum paramyosin could have important implications for the development of a S. japonicum vaccine.     

Host reactions in Biomphalaria glabrata to Schistosoma mansoni miracidia, involving variations in parasite strains, numbers and sequence of exposures

M-line Biomphalaria glabrata snails are susceptible to Puerto Rican (PR-1) strain of Schistosoma mansoni, but are resistant to a St. Lucian (LC-1) strain. 10-R2 B. glabrata snails are resistant to both strains of S. mansoni. When 10-R2 snails were exposed repeatedly to PR-1 S. mansoni miracidia for 5 consecutive days, all of the sporocysts were encapsulated and destroyed by the snails. Thirty-four per cent of sporocysts examined in M-line snails with similar exposures were also degraded. In double concurrent infections of M-line B. glabrata with [³H]leucine-labeled and unlabeled PR-1 and Lc-1 S. mansoni, the incompatible Lc-1 miracidia were selectively attacked and destroyed. This destruction occurred irrespective of the sequence of exposure of the 2 strains of miracidia, and whether or not the miracidia were labeled. Successful superinfection of M-line B. glabrata with homologous S. mansoni miracidia was obtained at least 4 days after the primary exposure to the miracidia.     

Schistosoma mansoni and Schistosoma japonicum: Utilization of amino acids

, , and 1972. Schistosoma mansoni and Schistosoma japonicum: utilization of amino acids. International Journal for Parasitology 2: 425–430. The production of ¹⁴CO₂ from 12 labeled amino acids by S. mansoni and S. japonicum was studied. No ¹⁴CO₂ was detected from incubations with glycine, isoleucine, leucine, lysine or phenylalanine. Differences were found between sexes and/or species for the other amino acids studied. Species related differences included a greater rate of metabolism of glutamic and aspartic acid by S. mansoni than by S. japonicum. Proline and histidine were utilized by S. mansoni males and females, respectively. S. japonicum male worms did not utilize proline, while histidine was not utilized by the female of this species. Major sex related differences included greater ¹⁴CO₂ production from glutamic acid, aspartic acid and arginine by S. mansoni males than by females, and the utilization of histidine by male S. japonicum but not by females. Incubation in tyrosine resulted in the release of only small amounts of ¹⁴CO₂ by female worms of both species but no ¹⁴CO₂ production by male worms.     

Studies on resistance in snails: Specific resistance induced by irradiated miracidia of Echinostoma lindoense in Biomphalaria glabrata snails

In juvenile Biomphalaria glabrata snails exposed to irradiated Echinostoma lindoense miracidia, the sporocysts migrated to the heart at the same speed as did nonirradiated sporocysts in control snails. However, in each snail so exposed to irradiated miracidia, amebocyte clumps in the snail's heart destroyed the sporocysts within 2–9 days post-exposure. This process induced a strong, highly specific resistance to homologous reinfection in these previously susceptible snails. The snails remained susceptible to Schistosoma mansoni and Paryphostomum segregatum (Echinostomatidae), but were partially resistant to Echinostoma paraensei and E. liei, two echinostome species closely related to E. lindoense.     

Studies on resistance in snails: A specific tissue reaction to Echinostoma lindoense in Biomphalaria glabrata snails

In juvenile albino Biomphalaria glabrata snails exposed for the first time to Echinostoma lindoense miracidia, and observed to be resistant, the sporocysts migrated to the heart at the same speed as they did in susceptible snails. However, in resistant snails the sporocysts were soon destroyed in the heart by amebocyte clumps. When these snails were then re-exposed to miracidia of the same species of trematode, the sporocysts were quickly destroyed soon after miracidial penetration, chiefly in the head-foot region. This strongly accelerated tissue reaction appears to have been induced by the previous contact with the same parasite. The sensitization of the snail tissues was highly specific: the hosts remained susceptible to Schistosoma mansoni and Paryphostomum segregation (Echinostomatidae), although partial resistance was observed against Echinostoma paraensei and E. liei, which are closely related to E. lindoense.     

Implication of Papio anubis in the transmission of intestinal schistosomiasis in three new foci in Kime area, Ethiopia.

Epidemiological studies were conducted in the Lake Langano area in the Rift Valley of Ethiopia to determine the occurrence of schistosomiasis and assess factors involved in its transmission. Microscopic examination of faecal specimens from free ranging Papio anubis (anubis baboon) troops from Bishan Gari and Burka Dita forest reserves revealed Schistosoma mansoni eggs with a prevalence of 12.1% (11/91) and 26.2%(34/130), respectively. The eggs were viable as confirmed by miracidial hatching and infectivity tests. Out of the total 12 communities (three schools, five villages and one herdsmen community) surveyed for schistosomiasis around Lake Langano, individuals excreting S. mansoni eggs were found in nine communities with prevalence of infection ranging from 1.4 to 43%. The intensity of infection ranged from 24 EPG (eggs per gram of faeces) to 243 EPG. Excretion of viable eggs by the baboons indicate that they play a role in maintenance of S. mansoni infection in the locality. The detection of S. mansoni eggs in young children, collection of cercarial-infected Biomphalaria pfeifferi in water bodies, and establishment of S. mansoni infection in lab-bred mice have confirmed establishment of transmission foci in Kime area, south-east of Lake Langano. However, the lake itself does not seem to support transmission of schistosomiasis since no snails were found along the shore of the Lake. Further investigations are indicated to fully elucidate the role baboons play in the epidemiology of schistosomiasis in the Rift Valley of Ethiopia. The risk of introduction of water-based development projects in these new endemic foci in relation to S. mansoni infection in the baboons is discussed.     

An Example of Circular Statistics in Chronobiological Studies: Analysis of Polymorphism in the Emergence Rhythms of Schistosoma Mansoni Cercariae

Chronobiological data concerning the emergence rhythms of Schistosoma mansoni cercariae were transformed into circular variables and analysed using circular statistics. The method proposed allowed three chronobiological patterns to be distinguished for the parasite populations studied, and statistical tests for the homogeneity of samples in each group and the significant differences between groups were also carried out.     

Cross-reactivity between Necator americanus and Schistosoma mansoni in mice.

, , and 1992. Cross-reactivity between Necator americanns and Schistosoma mansoni in mice. International Journal for Parasitology 22: 1143–1149. Poly-parasitism is common in endemic communities and reactivity of sera from hookworm-infected patients against schistosomular antigens has been reported. Protective cross-immunity between N. americanus and S. mansoni was investigated in NIH and BALB/c mice. Protective resistance to homologous challenge with both parasites was confirmed in this model, however, functional immunity to heterologous challenge was not demonstrated. Sera from animals which had received homologous challenge with N americanus and from hookworm-infected mice, which had previously been exposed to radiation-attenuated S. mansoni, exhibited an enhanced IgGAM response to infective stage N. americanus somatic antigens. The implications of these results with respect to serodiagnosis are discussed.     

A study of the death of Schistosoma mansoni cercariae during penetration of mammalian host skin: The influence of the ages of the cercariae and of the host

A study of the death of Schistosoma mansoni cercariae during penetration of mammalian host skin: the influence of the ages of the cercariae and of the host. International Journal for Parasitology 3: 789–794. The number of cercariae of S. mansoni which die during penetration of mouse abdominal skin steadily increases with age following emergence from the snail. An initial mortality level of about 30 per cent is observed for 2-h-old cercariae which rises to 50 per cent at 8 h and 85 per cent at 24 h. These increased losses in the skin are shown to account substantially for the known decrease in infectivity which accompanies ageing of cercariae. The number of cercariae which die in the skin of very young mice (2 days old) is less than one-third of the level in adult mice. Losses in the skin increase with age of the host up to about 28–35 days. This increased mortality in the skin is shown to account for the observed age resistance of mice, where fewer cercariae mature into adult worms in mice of 1 month or more, than in very young mice.     

A comparison of the glycolipid compositions of cercarial and adult Schistosoma mansoni and their associated hosts

Glycolipid patterns of cercarial and adult Schistosoma mansoni were determined and compared with those of Biomphalaria glabrata snails and mouse (BALB/c strain) red blood cells by high-performance thin-layer chromatography. Differences in glycolipid content were found between cercariae and adult worms and between these stages and their respective host tissues.     

Specificity of natural resistance to trematode infections in Biomphalaria glabrata

The 10-R2 strain of Biomphalaria glabrata was strongly resistant to various strains of Schistosoma mansoni in its laboratory of origin (NIH) and to three strains of S. mansoni we tested against it. However, subsequent development of three inbred lines of B. glabrata 10-R2 snails, separately maintained in our San Francisco laboratory, showed slight loss of resistance in one colony, very much less resistance (or partial susceptibility) in another, and retention of the original resistance in a third to the Puerto Rico (PR-1) strain of S. mansoni. No selection for resistance to infection was involved in the breeding protocol for these 10-R2 lines, so the changes were apparently random ones that became established in the separate inbred substrains. In spite of their changed response to the PR-1 strain of S. mansoni, all three 10-R2 substrains retained only slightly diminished resistance to S. mansoni Lc-1 strain and an essentially undiminished resistance to irradiated Echinostoma lindoense, E. paraensei and E. liei sporocysts. This suggests that natural resistance to S. mansoni PR-1 in B. glabrata is specific, a response that differs from the host response to either S. mansoni Lc-1 or to the echinostomes.     

Schistosoma Mansoni Miracidium Under Phase Difference Microscopy

The living, immobilized miracidium form of the Schistosoma mansoni has been photographed at the same plane under ordinary bright field and under phase contrast illumination. Under the latter method more of the internal structures are visible.     

Circadian Pattern of Cercarial Emergence in Schistosoma Mansoni(Platyhelminthes: Digenea) from Isolated Biomphalaria Glabrata

The present work aimed to compare the acrophases (peak hours) of emergence of Schistosoma mansoni cercariae among isolated individuals of the snail Biomphalaria glabrata. Laboratory stocks of melanic B. glabrata from the same biotope as the S. mansoni strain (Belo Horizonte, Minas Ger-ais) were used. Twenty-two snails individually exposed to five miracidia were tested. Chronobiological trials were performed outdoors after an acclimation period of at least a week. Three groups of snails were tested between November 1989 and April 1991. Cercarial emergence from individual isolated snails was quantified every 3 h for 3 consecutive days. In all trials, most cercariae were found to emerge during daytime (94.9%). Time series and chronograms showed recurrent peaks during the daytime. The periodogram suggested that 24 h was the period that best fitted cercarial emergence data in 90.9% of the snails. The single cosinor analysis confirmed 24-h rhythms in 95.5% of the snails. Acrophases of cercarial emergence among individual snails occurred between 14:15 and 17:02. They did not differ significantly. The population cosinor analysis indicated greater homogeneity in the 24-h rhythms of cercarial emergence than in the snail groups of each chronobiological trial. Acrophases of cercarial emergence occurred between 14:53 and 15:27 and did not differ significantly among all trials. Data from the three trials were pooled and analyzed using the population cosinor. This statistical method indicated a homogeneity in the 24-h rhythms of cercarial emergence from all snails, with acrophase occurring around 15:00. Results showed that the acrophases of cercarial emergence of S. mansoni are similar among isolated B. glubrura specimens. Data support the hypothesis of a “gate” rhythm in the dynamics of cercarial production and emergence. It is suggested that the adaptive importance of the “gate” mechanism is associated with the concentration of cercariae in the water at times when the vertebrate is present, optimizing the contact between the parasite and the host. The emergence of some cercariae at night (5.1% of the total number of emerged cercariae) suggests a flexible “gate” that could be associated with a residual light effect or with experimental procedures in the laboratory.     

Production of monoclonal antibodies against target schistosomal antigen secreted in the urine of Schistosoma mansoni-infected patients

This study was undertaken to develop an immunodiagnostic test of active human schistosomiasis mansoni using a monoclonal antibody which targets urinary schistosomal antigen. Polyclonal antisera raised in rabbits against the processed urine of Schistosoma mansoni-infected patients showed very high and significant reactivity with ES product of ova compared with other different S. mansoni antigens. The monoclonal antibody (4.23) was reactive with repetitive epitopes of S. mansoni soluble egg antigen and ES product of ova with molecular mass range of 65–23 kDa and 80–23 kDa, respectively. It recognised different stages of the parasite life-cycle, with no cross reaction with Fasciola or hydatid antigen. MAbs were characterised by isotyping, immunoelectrophoresis, SDS–PAGE and the enzyme-linked immunoelectrotransfer blot technique, ELISA, and their recognition of carbohydrate or protein antigenic epitopes by periodate oxidation and trichloroacetic acid treatment of the antigen. It was used for detection of circulating schistosomal antigen in an antigen capture antibody sandwich ELISA on sera and urines of 58 S. mansoni-infected patients, 17 S. haematobium-infected patients, 15 parasite-free negative healthy controls and sera from 13 schistosomiasis-free patients harbouring Fasciola or hydatid infections. The percentage sensitivity of the assay in the serum of S. mansoni-infected patients was 98.4% and in urine 94.8%. A positive correlation was found between the number of faecal S. mansoni eggs and the circulating antigen, both in serum and in urine. Antigen circulating in urine correlated with that in the sera of S. mansoni patients. These data provide a sensitive and non-invasive method almost comparable with the use of sera for immunodiagnosis of schistosomiasis and an indirect way to reflect the intensity of infection. Australian Society for Parasitology.     

Surface proteins on schistosomula and cercariae of Schistosoma mansoni

The surface proteins of schistosomula and cercariae of Schistosoma mansoni were examined by lactoperoxidase catalysed iodination followed by polyacrylamide gel electrophoresis. Two polypeptide chains were clearly labelled and they were present on both cercarial and schistosomular surfaces. A number of minor labelled components were also observed. The results suggest that membranes of the teguments of cercariae and schistosomula are similar.     

Mechanisms of resistance to S. mansoni infection: the rat model

Human schistosomiasis is associated with IgE and eosinophilia, feature of a type 2 response. In experimental investigations, murine model has been widely used in order to dissect the immune responses involved in the expression of protective immunity or disease in Schistosoma mansoni infection. Collectively, observations made in this model and in humans demonstrated a strong contrast since a Th2 response in infected mice is involved in the expression of pathology, however, in infected humans the same type of response is rather beneficial for the host. This review will consider the relevance of extrapolating studies of immune responses from experimentally infected rats a semi-permissive host, to studies on S. mansoni infected humans.