Studies on the molluscicidal activity of Agave angustifolia and Pittosporum tobira on schistosomiasis transmitting snails.

In the search for new molluscicidal plants for controlling the snail vectors of schistosomiasis, laboratory evaluation was made to assess the molluscicidal activity of Agave angustifolia and Pittosporum tobira plants against Biomphalaria alexandrina snails. Results indicated that both plants have promising molluscicidal activity as the LC90 of the dry powder of both plants was 120 ppm. Both plants showed marked cercaricidal and miracidicidal potencies against S. mansoni larvae. The LC90 of both plants (120 ppm) killed most B. alexandrina eggs within 24 h of exposure. The sub-lethal concentrations of both plants markedly suppressed the survival rate of B. alexandrina snails and the mortality increased with increasing the concentrations and the exposure period up to 10 successive weeks. The accumulative toxic effect of these concentrations was continuous during the recovery period. Also, the reproductive rates of exposed snails were greatly affected even through the recovery period. This depression in reproductive ability of snails was accompanied by histological damage in the hermaphrodite glands of exposed snails. Meanwhile, the growth of snails was estimated weekly and it showed great inhibition in exposed snails comparing with the control ones.

The roles of water, sanitation and hygiene in reducing schistosomiasis: a review.

Schistosomiasis is a disease caused by infection with blood flukes of the genus Schistosoma. Transmission of, and exposure to, the parasite result from faecal or urinary contamination of freshwater containing intermediate host snails, and dermal contact with the same water. The World Health Assembly resolution 65.21 from May 2012 urges member states to eliminate schistosomiasis through preventive chemotherapy (i.e. periodic large-scale administration of the antischistosomal drug praziquantel to school-aged children and other high-risk groups), provision of water, sanitation and hygiene (WASH) and snail control. However, control measures focus almost exclusively on preventive chemotherapy, while only few studies made an attempt to determine the impact of upgraded access to safe water, adequate sanitation and good hygiene on schistosome transmission. We recently completed a systematic review and meta-analysis pertaining to WASH and schistosomiasis and found that people with safe water and adequate sanitation have significantly lower odds of a Schistosoma infection. Importantly though, the transmission of schistosomiasis is deeply entrenched in social-ecological systems, and hence is governed by setting-specific cultural and environmental factors that determine human behaviour and snail populations. Here, we provide a comprehensive review of the literature, which explores the transmission routes of schistosomes, particularly focussing on how these might be disrupted with WASH-related technologies and human behaviour. Additionally, future research directions in this area are highlighted.

[Preventive effect of plant cercaricide Fangyouling for schistosome infection].

OBJECTIVE: To evaluate the preventive effect of Fangyouling (a plant cercaricide) for schistosome infection in the field. METHODS: Villagers contacting schistosome infested water in 3 administrative villages in Hubei Province were randomly selected, and the villagers rubbing Fangyouling before they contacted with the infested water were divided into Group I (159 cases) and those not rubbing Fangyouling before they contacted with the infested water were divided into Group II (172 persons). All the villagers were investigated by questionnaire, and their infections of schistosome were tested by sera and fecal examinations. RESULTS: There were no differences of constituent ratios of gender, age, occupation, time and type of infested water contact between the two groups (all P values > 0.05). The positive rates of sera and fecal examinations were 3.14% and 1.87%, respectively in Group I , and the positive rates of sera and fecal examinations were 9.30% and 6.40%, respectively in Group II, and there were significant differences between both the results of sera and fecal examinations of Group I and Group II (both P values < 0.05). In Group I , there were 110 people who completely embrocated Fangyouling, and their positive rates of sera and fecal examinations were 0.91% and 0, respectively. There are 42 people who incompletely embrocated Fangyouling, and their positive rates of sera and fecal examinations were 8.16% and 6.12%, respectively, and there were significant differences (both P values < 0.05). CONCLUSIONS: The preventive effect of schistosome infection of Fangyouling is significant. Incomplete embrocating may be one of the possible reasons for people still being infected with schistosome after rubbing the protective agent.

Development and validation of a quantitative, high-throughput, fluorescent-based bioassay to detect schistosoma viability.

BACKGROUND: Schistosomiasis, caused by infection with the blood fluke Schistosoma, is responsible for greater than 200,000 human deaths per annum. Objective high-throughput screens for detecting novel anti-schistosomal targets will drive 'genome to drug' lead translational science at an unprecedented rate. Current methods for detecting schistosome viability rely on qualitative microscopic criteria, which require an understanding of parasite morphology, and most importantly, must be subjectively interpreted. These limitations, in the current state of the art, have significantly impeded progress into whole schistosome screening for next generation chemotherapies. METHODOLOGY/PRINCIPAL FINDINGS: We present here a microtiter plate-based method for reproducibly detecting schistosomula viability that takes advantage of the differential uptake of fluorophores (propidium iodide and fluorescein diacetate) by living organisms. We validate this high-throughput system in detecting schistosomula viability using auranofin (a known inhibitor of thioredoxin glutathione reductase), praziquantel and a range of small compounds with previously-described (gambogic acid, sodium salinomycin, ethinyl estradiol, fluoxetidine hydrochloride, miconazole nitrate, chlorpromazine hydrochloride, amphotericin b, niclosamide) or suggested (bepridil, ciclopirox, rescinnamine, flucytosine, vinblastine and carbidopa) anti-schistosomal activities. This developed method is sensitive (200 schistosomula/well can be assayed), relevant to industrial (384-well microtiter plate compatibility) and academic (96-well microtiter plate compatibility) settings, translatable to functional genomics screens and drug assays, does not require a priori knowledge of schistosome biology and is quantitative. CONCLUSIONS/SIGNIFICANCE: The wide-scale application of this fluorescence-based bioassay will greatly accelerate the objective identification of novel therapeutic lead targets/compounds to combat schistosomiasis. Adapting this bioassay for use with other parasitic worm species further offers an opportunity for great strides to be made against additional neglected tropical diseases of biomedical and veterinary importance.

The impact of chemotherapy on morbidity due to schistosomiasis.

Current knowledge on the impact of chemotherapy on schistosomiasis-related morbidity is still fragmentary. In urinary schistosomiasis, reversal of organ pathology follows cure after 6 months and resurgence takes place after at least another 6 months. Retreatment after less than 1 year is, therefore, unnecessary. Also, intestinal schistosomiasis appears to regress promptly after chemotherapy. For the reversal of hepatic morbidity, more than one chemotherapy round appears necessary at least in foci of intense transmission of schistosomiasis. The earlier chemotherapy is given, the higher the chances of reversal of schistosomal pathology, but pathology may regress to some extent also in adults. The regression and resurgence of periportal fibrosis, as detected by ultrasonography, occurs with a delay of 7 months to more than 2 years after therapy. Retreatment after less than 1 year may not permit full assessment of the impact of the first round on hepatic morbidity. Children and adolescents should be the major target population, taking into account that in many foci, children out-of-school must be covered because they are at the highest risk. Repeated treatment during childhood may prevent the development of urinary tract disease in adulthood. However, no data are available on the prevention of genital pathology. Repeated chemotherapy may have a long term effect on re-infection intensities and the development of severe morbidity, even in foci where control has been interrupted for many years. Severe hepatic fibrosis may be prevented even in foci of intense transmission provided more than two rounds of chemotherapy have been given in childhood and that chemotherapy is available on demand. Chemotherapy has an important impact on child development, physical fitness and working capacity. Its effect on growth and anemia is improved by simultaneous treatment of intestinal parasites and the provision of adequate iron supplementation. The impact of chemotherapy on many of the multifaceted manifestations of schistosomiasis has not been assessed systematically. More data are needed on gallbladder pathology, neuroschistosomiasis, endocrinologic disorders, bladder cancer and co-infections with other pathogens. In areas where control has been achieved, the overall morbidity and mortality has decreased with a delay of many years or even decades.

The influence of colostrum on early Schistosoma mattheei infections in calves.

The study investigated whether the susceptibility of calves to an early Schistosoma mattheei infection may be modified by intake of colostrum from infected cows. Twelve calves born to non-infected mothers were randomly divided into 2 groups of 6. The animals from group 1 were fed colostrum originating from a pool collected from non-infected cows, the calves from group 2 received colostrum from a pool collected from cows infected with S. mattheei. One month after birth all calves were infected by exposure to 1000 cercariae of a local strain of S. mattheei, and perfused 12 weeks later to determine the worm- and tissue egg counts. IgG(H+L), IgG1, IgG2 and IgA levels against soluble adult worm antigen preparation of S. bovis (SWAP bovis) were analysed in both colostrum pools and in the serum from the calves collected during the study before and after receiving colostrum, then on days 7, 30, 73 and 122. Faecal egg counts were determined from day 73 onwards. The IgG(H+L), IgG1 and IgA levels of the positive colostrum pool were higher than those of the negative pool. Calves of group 2 showed significantly higher levels of IgG(H+L) and IgG1 until day 73, to reach equal levels at necropsy. Calves of group 2 showed significant reductions of 42, 28 and 42% in total worm counts, female worm counts, and tissue egg counts, respectively, and a reduction of 25% in cumulative faecal egg counts. These findings indicate that there was a significant impact of colostrum on the parasitological and serological course of early S. mattheei infections.

Schistosome calcium channel beta subunits. Unusual modulatory effects and potential role in the action of the antischistosomal drug praziquantel.

Schistosomes are parasitic flatworms that cause schistosomiasis, a major tropical disease. The current drug of choice against schistosomiasis is praziquantel (PZQ), which has minimal side effects and is potent against all schistosome species. The mode of action of PZQ is unknown, though the drug clearly affects Ca(2+) homeostasis in worms, and there is indirect evidence for interaction of PZQ with schistosome voltage-gated Ca(2+) channels. We have cloned and expressed two Ca(2+) channel beta subunits, one from Schistosoma mansoni and one from Schistosoma japonicum. These two subunits (SmCa(v)beta A and SjCa(v)beta) have structural motifs that differ from those found in other known beta subunits. Surprisingly, coexpression of either SmCa(v)beta A or SjCa(v)beta with a cnidarian (CyCa(v)1) or mammalian (Ca(v)2.3) Ca(2+) channel alpha(1) subunit results in a striking reduction in current amplitude. In the case of Ca(v)2.3, this current reduction can be partially reversed by addition of 100 nm PZQ, which results in a significant increase in current amplitude. Thus, these unusual schistosome beta subunits can confer PZQ sensitivity to an otherwise PZQ-insensitive mammalian Ca(2+) channel, indicating that a possible target for PZQ action is the interaction between beta subunits and pore-forming alpha(1) subunits in schistosomes.

In vivo, attenuation of schistosome cercarial development and disturbance of egg laying capacity in Biomphalaria alexandrina using sublethal concentrations of plant molluscicides.

The dry powdered of Sinapis arvensis, Thymelaea hirsuta, Callistemon lanceolatus and Peganum harmala showed molluscicidal activity against Biomphalaria alexandrina, specific intermediate hosts to Schistosoma mansoni. Effect of LC25 of dry powdered plant molluscicides on hexokinase (HK), glucose phosphate isomerase (GPI), AMP deaminase, adenosine deaminase and phenol oxidase (PO) of B. alexandrina was traced. C. lanceolatus showed the highest molluscicidal activity as it has the lowest LC50 compared to S. arvensis, T. hirsuta, and P. harmala. LC25 of the latter three plants resulted in more significant inhibition of HK, GPI, AMP-deaminase and PO than C. lanceolatus. Treatment of snails with LC10 of these plants markedly affected compatibility of B. alexandrina to S. mansoni infection. Significant decrease in cercarial production recorded in snails treated with sublethal concentrations of S. arvensis, T. hirsuta, and P. harmala. Remarkable impairment of the egg laying capacity of molluscicide-treated snails was also recorded. Correlation between activity levels of HK, GPI and AMP deaminase and compatibility to parasitic infection and role of PO in the egglaying capacity of these snail species were discussed.

Development of bait formulations for control of intermediate hosts of African schistosome species.

Exploration of methods of snail control indicated a need for a new method because many failures in control programmes are due to lack of contact between molluscicides and the target snail population. The incorporation of molluscicides inside food pellets that are attractive to and ingestible by the target snails is suggested. Different concentrations of alcoholic extracts of Ambrosia maritima, Cucumis prophetarum and Rhynchosia minima-molluscicides of plant origin-were compared with niclosamide (Bayluscide) which is a strong synthetic molluscicide. They were incorporated into attractive food pellets and the lethal doses were determined. The results showed that Biomphalaria alexandrina snails are sensitive to only bait formulations with low concentrations of molluscicides. Laboratory and semi-field trials were conducted to study the efficacy of the prepared bait formulations on Biomphalaria alexandrina snails. The stability of these bait formulations was studied and it was observed that their effectiveness was reduced after long storage periods (> 3 weeks). The results revealed that Ambrosia maritima was the most effective molluscicide.

Plant molluscicides: potential of Aridan, Tetrapleura tetraptera, for schistosomiasis control in Nigeria.

Molluscicides are crucial for the control of schistosomiasis. The need to use plant molluscicides has received increased interest as an inexpensive technology because of the high cost of synthetic compounds for snail control in the endemic areas of poor nations of the world. Laboratory screening of Nigerian medicinal plants has shown that some of these contain chemicals which are among the most potent natural molluscicides available today. Field trials have been carried out on Tetrapleura tetraptera, locally known as Aridan, which is widely distributed in West Africa and can be collected and processed locally for the control of schistosomiasis. Research efforts in identifying botanical molluscicides, such as Aridan, should be encouraged by strong support, both from the Government and the private sector, in a current period of economic depression.