Snail-Related Contributions from the Schistosomiasis Consortium for Operational Research and Evaluation Program Including Xenomonitoring, Focal Mollusciciding, Biological Control, and Modeling

The Schistosomiasis Consortium for Operational Research and Evaluation (SCORE) was created in 2008 to answer questions of importance to program managers working to reduce the burden of schistosomiasis in Africa. In the past, intermediate host snail monitoring and control was an important part of integrated schistosomiasis control. However, in Africa, efforts to control snails have declined dramatically over the last 30 years. A resurgence of interest in the control of snails has been prompted by the realization, backed by a World Health Assembly resolution (WHA65.21), that mass drug administration alone may be insufficient to achieve schistosomiasis elimination. SCORE has supported work on snail identification and mapping and investigated how xenomonitoring techniques can aid in the identification of infected snails and thereby identify potential transmission areas. Focal mollusciciding with niclosamide was undertaken in Zanzibar and Côte d'Ivoire as a part of elimination studies. Two studies involving biological control of snails were conducted: one explored the association of freshwater riverine prawns and snail hosts in Côte d'Ivoire and the other assessed the current distribution of Procambarus clarkii, the invasive Louisiana red swamp crayfish, in Kenya and its association with snail hosts and schistosomiasis transmission. SCORE also supported modeling studies on the importance of snail control in achieving elimination and a meta-analysis of the impact of molluscicide-based snail control programs on human schistosomiasis prevalence and incidence. SCORE's snail control studies contributed to increased investment in building capacity, and specimens collected during SCORE research deposited in the Schistosomiasis Collections at the Natural History Museum (SCAN) will provide a valuable resource for the years to come.

Sympatric versus allopatric evolutionary contexts shape differential immune response in Biomphalaria / Schistosoma interaction

Selective pressures between hosts and their parasites can result in reciprocal evolution or adaptation of specific life history traits. Local adaptation of resident hosts and parasites should lead to increase parasite infectivity/virulence (higher compatibility) when infecting hosts from the same location (in sympatry) than from a foreign location (in allopatry). Analysis of geographic variations in compatibility phenotypes is the most common proxy used to infer local adaptation. However, in some cases, allopatric host-parasite systems demonstrate similar or greater compatibility than in sympatry. In such cases, the potential for local adaptation remains unclear. Here, we study the interaction between Schistosoma and its vector snail Biomphalaria in which such discrepancy in local versus foreign compatibility phenotype has been reported. Herein, we aim at bridging this gap of knowledge by comparing life history traits (immune cellular response, host mortality, and parasite growth) and molecular responses in highly compatible sympatric and allopatric Schistosoma/Biomphalaria interactions originating from different geographic localities (Brazil, Venezuela and Burundi). We found that despite displaying similar prevalence phenotypes, sympatric schistosomes triggered a rapid immune suppression (dual-RNAseq analyses) in the snails within 24h post infection, whereas infection by allopatric schistosomes (regardless of the species) was associated with immune cell proliferation and triggered a non-specific generalized immune response after 96h. We observed that, sympatric schistosomes grow more rapidly. Finally, we identify miRNAs differentially expressed by Schistosoma mansoni that target host immune genes and could be responsible for hijacking the host immune response during the sympatric interaction. We show that despite having similar prevalence phenotypes, sympatric and allopatric snail-Schistosoma interactions displayed strong differences in their immunobiological molecular dialogue. Understanding the mechanisms allowing parasites to adapt rapidly and efficiently to new hosts is critical to control disease emergence and risks of Schistosomiasis outbreaks.

Schistosomiasis, the second most widespread human parasitic disease after malaria, is caused by helminth parasites of the genus Schistosoma. More than 200 million people in 74 countries suffer from the pathological, and societal consequences of this disease. To complete its life cycle, the parasite requires an intermediate host, a freshwater snail of the genus Biomphalaria for its transmission. Given the limited options for treating Schistosoma mansoni infections in humans, much research has focused on developing methods to control transmission by its intermediate snail host. Biomphalaria glabrata. Comparative studies have shown that infection of the snail triggers complex cellular and humoral immune responses resulting in significant variations in parasite infectivity and snail susceptibility, known as the so-called polymorphism of compatibility. However, studies have mostly focused on characterizing the immunobiological mechanisms in sympatric interactions. Herein we used a combination of molecular and phenotypic approaches to compare the effect of infection in various sympatric and allopatric evolutionary contexts, allowing us to better understand the mechanisms of host-parasite local adaptation. Learning more about the immunobiological interactions between B. glabrata and S. mansoni could have important socioeconomic and public health impacts by changing the way we attempt to eradicate parasitic diseases and prevent or control schistosomiasis in the field.

Human schistosomiasis in the post mass drug administration era

Profound changes are occurring in the epidemiology of schistosomiasis, a neglected tropical disease caused by a chronic infection with parasitic helminths of the genus Schistosoma. Schistosomiasis currently affects 240 million people worldwide, mostly in sub-Saharan Africa. The advent and proliferation of mass drug administration (MDA) programmes using the drug praziquantel is resulting in substantial increases in the number of people, mainly children aged 6-14 years, being effectively treated, approaching the point where most people in endemic areas will receive one or more treatments during their lifetimes. Praziquantel treatment not only cures infection but also frees the host from the powerful immunomodulatory action of the parasites. The treatment simultaneously enhances exposure to key parasite antigens, accelerating the development of protective acquired immunity, which would take many years to develop naturally. At a population level, these changes constitute a substantial alteration to schistosome ecology in that the parasites are more likely to be exposed not only to praziquantel directly but also to hosts with altered immune phenotypes. Here, we consider the consequences of this for schistosome biology, immunoepidemiology, and public health. We anticipate that there could be substantial effects on chronic pathology, natural immunity, vaccine development strategies, immune disorders, and drug efficacy. This makes for a complex picture that will only become apparent over decades. We recommend careful monitoring and assessment to accompany the roll-out of MDA programmes to ensure that the considerable health benefits to populations are achieved and sustained.

[Effects of Schistosoma 22.6 kDa/26 GST molecule mixed with Sepharose 4B beads on induction of CD4+CD25+ regulatory T cells]

OBJECTIVE

To study the responses of regulatory T cells induced by Sepharose 4B beads mixed antigen.

METHODS

Mice were immunized with different dosages of antigens, and the proportions of regulatory T cells were examined by flow cytometry. The 3H-thymidin incorporation method was used to detect the inhibitory function of Tregs. In vitro, dendritic cells were pulsed with different antigens. The expressions of MHC II, CD40, CD80/86 molecules on dendritic cells and the proportions of regulatory T cells were examined by flow cytometry. The 3H-thymidin incorporation method was used for the determination of Tregs function.

RESULTS

Compared with control groups, the proportion of regulatory T cells in mice immunized with Sepharose 4B beads mixed antigen was(11.48 +/- 4.12)%, and the difference was significant (P < 0.05). The inhibition of regulatory T cells in mice immunized with Sepharose 4B beads mixed antigen showed a stronger potential (cpm was 720 +/- 180.4). Meanwhile, the proportions of regulatory T cells were (17.0 +/- 80.57)% and (30.14 +/- 3.62)% when the CD4+ T cells were co-cultured with dendritic cells pulsed with Sepharose 4B beads mixed rSj22.6/26GST and OVA, respectively.

CONCLUSION

Sepharose 4B beads mixed antigen could induce the regulatory T cells in vivo and in vitro.

Community acceptability of the use of low-dose niclosamide (Bayluscide), as a molluscicide in the control of human schistosomiasis in Sahelian Cameroon

Although field trials of the application of molluscicides for the control of human schistosomiasis have been conducted in several settings, the acceptability of molluscide use at the community level has been poorly documented. The death and putrefaction of aquatic organisms in water treated with niclosamide (Bayluscide), for example, and the yellowish colouration of such water, may decrease the molluscide's acceptability. It may be possible, however, to use doses of a molluscicide that are only just high enough to kill the target snails but not high enough to kill non-target fish and frogs, thereby reducing the application's impact on water quality and colour and improving its acceptability to local communities. In a study in northern Cameroon, Bayluscide WP70 was applied to ponds at concentrations of 0, 0.25, 0.5 or 1 g/m(3). Changes in human contact with the water in the ponds were explored both by direct observation and by in-depth interviews with key informants from the local community. Although all applications of niclosamide greatly decreased human use of the treated ponds for a few days, most informants (99%) were in favour of niclosamide application and only 6% of the interviewees gave change in water colour or bad smell as a reason for not using a particular water body. Over the few days post-application, use of ponds treated with 0.25 or 0.5 g Bayluscide WP70/m(3) was higher than that of the ponds treated with 1 g/m(3), indicating that relatively low-dose applications, if effective in controlling snails, may be more acceptable to local communities than applications at higher doses.

Parasitic central nervous system infections: echinococcus and schistosoma

Central nervous system (CNS) manifestations of Echinococcus and Schistosoma infections occur throughout the world, with incidence increasing in developed regions. A detailed literature review generated a current summary on epidemiology, parasitology, pathology, clinical manifestations, imaging studies, diagnosis, and treatment of neuroechinococcosis and neuroschistosomiasis. Recent advancements have been made in diagnosis, treatment, and prevention of these parasitic CNS infections. Ongoing advancements in neuroimaging and diagnostic studies, as well as efforts to better understand the parasite genome and host-parasite relationships, will likely continue to improve patient management.

Worms take the 'phyto' out of 'phytochelatins'

Phytochelatin synthase is the enzyme responsible for the synthesis of heavy-metal-binding peptides (phytochelatins) from glutathione and related thiols. It has recently been determined that it is not only restricted to plants and some fungi, as was once thought, but also has an essential role in heavy-metal detoxification in the model nematode Caenorhabditis elegans. These findings and others that demonstrate phytochelatin synthase-coding sequences in the genomes of several other invertebrates, including pathogenic nematodes, schistosomes and roundworms, herald a new era in phytochelatin research, in which these novel post-translationally synthesized peptides will not only be investigated in the context of phytoremediation but also from a clinical parasitological standpoint.

DNA therapy for asthma

Asthma therapy, like other therapies, has been moving towards a molecular basis for several years. This year, there have been several preclinical studies published which utilize attributes or facets of DNA to address asthma therapeutics. These include antisense oligonucleotides (against the nuclear transcription factor GATA-3 and the mast cell chemotactic agent, stem cell factor), gene transfer (of interleukin-18, both by plasmid and viral vectors), and CpG oligodeoxynucleotides (which suppress Th2 and stimulate Th1 responses). No clinical experience has yet been reported for any of these areas of research in asthma, but clinical trials are ongoing utilizing CpG oligonucleotides.

Transient expression of DNA and RNA in parasitic helminths by using particle bombardment

Parasitic helminths (worms belonging to several metazoan phyla) cause considerable morbidity and mortality in humans. They are an important veterinary problem, and they result in significant economic losses in animal grazing and agriculture. Experimental studies on parasitic helminths have been limited by a lack of parasite cell lines and methods for molecular genetic analyses. We evaluated particle bombardment (biolistics) as a strategy to introduce and express nucleic acids in these multicellular parasites. By using embryos of the parasitic nematode Ascaris as a model, we developed methods to introduce and express both DNA and RNA during several stages of Ascaris embryogenesis. Biolistic transfection will facilitate experimental strategies in Ascaris embryos complementing other biochemical tools available (e.g., in vitro whole-cell embryo extracts for transcription, RNA processing, and translation). Transfection experiments with adult schistosomes further suggest that the biolistic strategy should be applicable to a variety of other parasitic helminths. The development of these methods provides molecular genetic tools to study gene expression and the biology of a variety of types and developmental stages of important helminth parasites.

The effects of miracidal aging and dilution of snail-conditioned water on responses of miracidia of Megalodiscus temperatus

Miracidia of Megalodiscus temperatus from newly hatched until 10 hr old were tested for their ability to react to Helisoma trivolvis snail-conditioned water (SCW) by contact with return (CR) to agar blocks and by percentage of miracidia reacting to a point inoculation of SCW as determined by a photographic time exposure method. CR to agar blocks containing 1:50 SCW was greatest during the first 6 hr after hatching but declined thereafter. The reaction during the first hour to a point inoculation was lower than during the 2nd and 3rd hr. Results were variable from 4 to 10 hr after hatching with the lowest response recorded from 9 to 10 hr. Miracidial responses to dilutions of SCW were assessed by the same two methods. CR to agar blocks containing decreasing concentrations of SCW declined until at a dilution of 1:500 CR was only slightly above the controls. On the other hand, miracidial reactions to point inoculations of SCW as determined by the photographic method were still apparent at a dilution of 1:25,000, when 12% of the miracidia tested reacted. Thus, the photographic time exposure method gives a sensitive means for detecting altered miracidial behavior to various intrinsic and extrinsic factors.

Further studies on the compatibility between s. intercalatum from cameroun and zaïre and species of bulinus

The results from the infection experiments with Schistosoma intercalatum from Cameroun and from Zaïre and the intermediate hosts, belonging to B. forskalii and B. globosus, could be divided into groups according to the degree of compatibility with the schistosomes. This was indicated by the total cercariae production per 100 exposed snails (TCP/100 exp. snails). B. forskalii from Kinshasa, Zaïre were the snails which were most compatible with S. intercalatum from Cameroun, and B. globosus populations tested were refractory. The TCP/100 exposed snails was about 300,000 for the populations of B. forskalii from Kinshasa compared with the low production for B. forskalii from Cameroun of 125,000. B. wrighti from South Arabia produced 155,000 cercariae per 100 exposed snails. B. cernicus from Mauritius could be separated into two types according to the compatibility with S. intercalatum from Cameroun, the TCP/100 exposed snails was 31,000 and 267,000, respectively. B. globosus from Kinshasa, Zaïre, was very compatible with S. intercalatum from Zaïre and the TCP/100 exposed snails was very high, and 300,000. An albino strain of B. globosus from Rhodesia was the most compatible snail having a TCP/100 exposed snails of 2.4 million cercariae. Other strains of B. globosus from Cameroun and Togo were refractory and less susceptible. It was also possible to infect B. africanus and the two tested populations from Kenya and Tanzania, producing 15,000 and 179,000 cercariae per 100 exposed snails, respectively.

[Numerical variation of ciliated papillae in the miracidia of different strains of Schistosoma mansoni, the organism producing intestinal bilharzia]

In the miracìdia of 13 strains of Schistosoma mansoni, silver impregnation points out variations in the number of ciliated papillae situated between tiers 2 and 3 of epidermal cells, correlative with the size of the miracidia. These variations are related to the intermediate and definitive hosts. The number of ciliated papillae gives objective information on the degree of adaptation between the parasite and its successive hosts.