SWOT analysis on snail control measures applied in the national schistosomiasis control programme in the People's Republic of China.

BACKGROUND: Snail control is an important component in the national schistosomiasis control programme in China, by application of chemical molluscicides, forestry projects, agriculture projects and water conservancy projects in recent decades. However, there are still wide areas of snail inhabited in China which remains a great challenge to achieve the goal of schistosomiasis elimination by 2025. Therefore, a SWOT (strengths, weaknesses, opportunities and threats) analysis on snail control measures is required for precision schistosomiasis control. METHODS: The SWOT approach, which is a well-known structured analysis tool, was used to identify and evaluate the specific characteristics of four types of snail control measures in China, including chemical mollusciciding, forestry, agriculture, and water conservancy projects. The analysis were carried out based on the information collection from literature review, of research papers, books, annual report database of national schistosomiasis control programme in China, reports from the academic forums, and so on. RESULTS: For chemical mollusciciding, application strategy needs to focus on specific local settings, such as stage of schistosomiasis control, environmental factors, and limitations from external policies and internal deficiencies. Regarding forestry projects, the optimal strategies are to cooperate with other national forestry programmes to share the investment costs and pay attention on wetland protection. In agriculture projects, it is necessary to develop related cash crop industries and combine with national farmland consolidation projects simultaneously to increase the total economic benefits. Concerning water conservancy projects, the main purpose is to control snail migration from snail area to snail-free areas nationwide. CONCLUSIONS: Integrated strategies for various measures application and a top-level designed cooperation mechanism will be the necessary to eliminate snail and schistosomiasis in China.

Schistosomiasis Transmission Model and its Control in Anhui Province.

National Bureau of Statistics of China reports that the incidence of schistosomiasis has been increasing in recent years. To study dynamic behaviors of schistosomiasis transmission, based on practical experience of staff in Anhui Institute of Schistosomiasis, a mathematical schistosomiasis model with reinfection of recovered people is established in this paper. Metzler matrix theory and center manifold theorem are used to analyze stability of equilibria. Parameter estimation has been performed by combining model and monitoring data. It is found that the basic reproduction number is different every year. The most concern of Institute of Schistosomiasis is whether or when to kill snails every year. To answer this question, threshold value of snail density can be obtained. Once the snail density exceeds the threshold, the staff will need to kill snails. To find the best control measures, sensitivity analysis is used to find out sensitive parameters, and then control measures can be obtained by optimization control measures. The results show that combination of spraying molluscicide, publicity and education, improving the health facilities, and large-scale treatment of patient groups have the best effect. In additional, it is found that the number of patients does not change much when the reinfection rate of recovered people is very small. However, when the reinfection rate is slightly larger, the number of patients will suddenly increase to a large value.

Barbatic Acid Offers a New Possibility for Control of Biomphalaria Glabrata and Schistosomiasis.

This study evaluated the biological activity of an ether extract and barbatic acid (BAR) from Cladia aggregata on embryos and adult mollusks of Biomphalaria glabrata, cercariae of Schistosoma mansoni and the microcrustacean Artemia salina. The ether extract and BAR were obtained by successive extractions with diethyl ether. The obtained extracts were analyzed using thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC), proton nuclear magnetic resonance (¹H-NMR) and infrared (IR) spectroscopy. The results demonstrated that the ether extract exerted embryotoxic effects at 50 and 100 µg/mL and molluscicidal effects at 20 and 25 µg/mL. BAR exhibited no embryotoxicity, and its molluscicidal concentration was equal to that of the ether extract. However, after 60 min of exposure, 1 µg/mL BAR presented cercaricidal activity against the parasite S. mansoni at the second larval stage. Neither substance induced toxicity against A. salina. These results indicate the potential molluscicidal activities of the ether extract and BAR against B. glabrata and S. mansoni cercariae. In addition to these effects, there was a lack of toxicity against the aquatic environment and no damage to the biota, indicating the potential of these products for large-scale control and/or eradication of schistosomiasis.

[Research progress on the molluscicidal effect of niclosamide compounded with other molluscicides against Oncomelania hupensis].

Niclosamide is the only molluscicide recommended by the World Health Organization. It is effective for snail control but have some disadvantages. Therefore, the research goal is to increase the molluscicidal activity of niclosamide and reducing its defects. This article reviews the research advances on the molluscicidal effect of niclosamide compounded with other molluscicides against Oncomelania hupensis.

Long term study on the effect of mollusciciding with niclosamide in stream habitats on the transmission of schistosomiasis mansoni after community-based chemotherapy in Makueni District, Kenya.

BACKGROUND: Schistosoma mansoni infection is a persistent public health problem in many Kenyan communities. Although praziquantel is available, re-infection after chemotherapy treatment is inevitable, especially among children. Chemotherapy followed by intermittent mollusciciding of habitats of Biomphalaria pfeifferi, the intermediate host snail, may have longer term benefits, especially if timed to coincide with natural fluctuations in snail populations. METHODS: In this cohort study, the Kambu River (Intervention area) was molluscicided intermittently for 4 years, after mass chemotherapy with praziquantel in the adjacent community of Darajani in January 1997. The nearby Thange River was selected as a control (Non-intervention area), and its adjacent community of Ulilinzi was treated with praziquantel in December 1996. Snail numbers were recorded monthly at 9-10 sites along each river, while rainfall data were collected monthly, and annual parasitological surveys were undertaken in each village. The mollusciciding protocol was adapted to local conditions, and simplified to improve prospects for widespread application. RESULTS: After the initial reduction in prevalence attributable to chemotherapy, there was a gradual increase in the prevalence and intensity of infection in the non-intervention area, and significantly lower levels of re-infection amongst inhabitants of the intervention area. Incidence ratio between areas adjusted for age and gender at the first follow-up survey, 5 weeks after treatment in the non-intervention area and 4 months after treatment in the intervention area was not significant (few people turned positive), while during the following 4 annual surveys these ratios were 0.58 (0.39-0.85), 0.33 (0.18-0.60), 0.14 (0.09-0.21) and 0.45 (0.26-0.75), respectively. Snail numbers were consistently low in the intervention area as a result of the mollusciciding. Following termination of the mollusciciding at the end of 2000, snail populations and infections in snails increased again in the intervention area. CONCLUSION: The results of this study demonstrate that in the Kenyan setting a combination of chemotherapy followed by intermittent mollusciciding can have longer term benefits than chemotherapy alone.

Molluscicidal and antiparasitic activity of Solanum nigrum villosum against Galba truncatula infected or uninfected with Fasciola hepatica.

The present study was based on assessments of the molluscicidal and antiparasitic activities of Solanum nigrum villosum. This plant has been collected in Tozeur's traditional oases (south-western Tunisia). Molluscicidal activities of leaves, ripe fruit and unripe fruit extracts of S. n. villosum have been assessed in experimental and semi-field conditions on uninfected Galba truncatula. Antiparasitic activities have also been assessed on larval stages (rediae, intraredial germinal masses and cercariae) of the parasite Fasciola hepatica infecting G. truncatula naturally. The unripe fruit extract (LC50 = 41.2 mg l- 1) was more toxic than the leaf (LC50 = 132.5 mg l- 1) and the ripe fruit (LC50 = 172.8 mg l- 1) extracts on the snail after 48 h of treatment. One mg l- 1 of cupric chloride produced the death of 97% of G. truncatula after 25 days of treatment. Solanum n. villosum extracts used at the lethal laboratory concentration in semi-field conditions were also toxic to G. truncatula. The unripe fruit extract was more toxic than the leaf and the ripe fruit extracts on larval stages of F. hepatica. Maximum deterioration rates were obtained with the unripe fruit extract: 65.6% for rediae, 77.8% for cercariae and 27.6% for intraredial germinal masses after 48 h of treating the snails. The possibility of the unripe fruit extract application for the control of G. truncatula and F. hepatica larval stages should be considered.

Commiphora molmol extracts as plant molluscicide against Lymnaea natalensis.

Two extracts from the herbal plant, Commiphora molmol showed a high molluscicidal effect against Lymnaea natalensis. The oil extract was more potent than the oleo-resin. A concentration of 10 ppm of the oil extract killed 100% of L. natalensis after 5th day, but the oleo-resin extract killed 100% of them at a concentration 20 ppm after 5th day.

Commiphora molmol in human welfare (review article).

The origins of myrrh and frankincense are traced to the Arabian Peninsula. According to Herodotus (5th century BC): "Arabia is the only country which produces frankincense, myrrh, cassia and cinnamon ... the trees bearing the frankincense are guarded by winged serpents of small size and various colors." Diodorus Siculus writes, in the second half of the first century BC, that "all of Arabia exudes a most delicate fragrance; even the seamen passing by Arabia can smell the strong fragrance that gives health and vigor." He also mentioned gold mines so pure that no smelting was necessary. The Magi, carrying myrrh, frankincense, and gold, came from the East: Arabia. The frankincense trade route, with transport by donkeys and later by camel caravans, reached Jerusalem and Egypt from the Dhofar region of what is today Oman, through Yemen, turning north to follow the Red Sea coast. It is likely that the same or similar species of the resin-bearing plants grew across the Red Sea in the area that is now Somalia and Ethiopia, while the collection of the gum resins was initiated in Arabia. Myrrh contributed much in the human welfare. This review selected some but not all of the value application of myrrh (Commiphora molmol).

Molluscicidal activity of Solanum species of the Northeast of Brazil on Biomphalaria glabrata.

Seven species of Solanum were screened for their molluscicidal properties against Biomphalaria glabrata, the intermediated host of Schistosoma mansoni, Solanum agrarium, S. jabrense, S. melissarum, S. megalonyx, S. paludosum, S. paraibanum and S. stipulaceum. Four extracts showed molluscicidal activity with LC(50) from 22 to 56 microg/ml.

Screening of Echinops ellenbeckii and Echinops longisetus for biological activities and chemical constituents.

Members of the genus Echinops in the family of Asteraceae are widely used in Ethiopian herbal medicine for the treatment of various diseases and illness such as migraine, diarrhea, heart pain, different forms of infections, intestinal worm infestation and hemorrhoid. Hydroalcoholic extracts of the root, flower head, leaf and stem of Echinops ellenbeckii O. Hoffm. and Echinops longisetus A. Rich were investigated for their chemical constituents and biological activities. The presence of alkaloids, saponins, phytosterols, polyphenols and carotenoids in the different parts of the plants was observed whilst anthraquinones were not detected. The leaf extracts of both plants and stem extract of E. longisetus showed strong inhibitory activity against cultures of Staphylococcus aureus. None of the extracts were found to be active against Gram-positive organisms. The flower extract of E. ellenbeckii showed strong inhibitory activity against Candida albicans. Root and flower extracts of the plants investigated showed lethal activity against earthworms. Moreover, the extracts of the roots of both plants showed molluscicidal activity against schistosome-transmitting snail hosts. The biological activities observed were dose dependent.

Control of Biomphalaria pfeifferi population and schistosomiasis transmission in Ethiopia using the soap berry endod (Phytolacca dodecandra), with special emphasis on application methods.

The endod (Phytolacca dodecandra)-based schistosomiasis mansoni control project was implemented in Ethiopia between 1994 and 1999. The aim was to develop an effective, cheap and sustainable method of controlling schistosomiasis. First, different formulations of the Ethiopian endod strain 44 (E-44) were compared for potency in the laboratory. Secondly, spray and drip-feeding methods were compared for simplicity and effectiveness in the field. Lastly, the efficacy of endod powder soap was compared with the endod spray method. In Bati stream, endod powder soap was distributed to the residents every weekend at laundry sites. In Worke stream, endod was sprayed along a 1-km stretch of the stream at 3-month intervals. No endod was applied in Harbu stream. The immediate and long-term effects of endod application on the snail population and schistosomal infection were determined. Using the spray method, 100% snail mortality could be obtained, and it was simpler and more effective than the drip-feeding method. Snail mortality ranged from 20 to 100% using endod soap. There was a progressive decline in the snail population and infection in Bati stream compared with Worke stream, mainly due to sustained use of endod soap. The advantages and disadvantages of the different endod delivery systems are discussed.

Schistosomiasis control in China: the impact of a 10-year World Bank Loan Project (1992-2001).

China has been carrying out large-scale schistosomiasis control since the mid-1950s, but in the early 1990s, schistosomiasis was still endemic in eight provinces. A World Bank Loan Project enabled further significant progress to be made during the period 1992-2001. The control strategy was focused on the large-scale use of chemotherapy -- primarily to reinforce morbidity control -- while at the same time acting on transmission with the ultimate goal of interrupting it. Chemotherapy was complemented by health education, chemical control of snails and environmental modification where appropriate. A final evaluation in 2002 showed that infection rates in humans and livestock had decreased by 55% and 50%, respectively. The number of acute infections and of individuals with advanced disease had also significantly decreased. Although snail infection rates continued to fluctuate at a low level, the densities of infected snails had decreased by more than 75% in all endemic areas. The original objectives of the China World Bank Loan Project for schistosomiasis control had all been met. One province, Zhejiang, had already fulfilled the criteria for elimination of schistosomiasis by 1995. The project was therefore a success and has provided China with a sound basis for further control.

Biological screening of Nigella damascena for antimicrobial and molluscicidal activities.

The essential oil, various extracts at different polarity, fractions, and pure compounds obtained from Nigella damascena plants and seeds were screened for biological activity. Antimicrobial tests showed the essential oil to be active only against Gram positive bacteria; among the extracts, the BuOH was active against Pseudomonas aeruginosa and Staphylococcus aureus. Molluscicidal activity was absent.

Molluscicidal and antimicrobial activity of Solanum aculeastrum.

The methanolic extract of the fresh root bark and berries of Solanum aculeastrum showed significant activity against host snails of schistosomiasis. The berries extract was more potent with 100% snail kill at 50 ppm. Fractionation increased activity with 100% mortality at 20 ppm. The aqueous and methanolic extracts of the berries showed moderate antimicrobial activity, increasing by fractionation.

Achievement of the World Bank loan project on schistosomiasis control (1992-2000) in Hubei province and the challenge in the future.

Since the World Bank provided a loan for control of schistosomiasis in China, started from 1992, with the objective of a reduction of prevalence and intensity of the infection both in humans and animals by 40%, through mass chemotherapy in areas of high prevalence, and selective chemotherapy in areas with medium and low endemicity together with focal mollusciciding, the objective of morbidity control of the project has been reached in Hubei Province.

Mathematical modelling of schistosomiasis japonica: comparison of control strategies in the People's Republic of China.

We present the first mathematical model on the transmission dynamics of Schistosoma japonicum. The work extends Barbour's classic model of schistosome transmission. It allows for the mammalian host heterogeneity characteristic of the S. japonicum life cycle, and solves the problem of under-specification of Barbour's model by the use of Chinese data we are collecting on human-bovine transmission in the Poyang Lake area of Jiangxi Province in China. The model predicts that in the lake/marshland areas of the Yangtze River basin: (1) once-yearly mass chemotherapy of humans is little better than twice-yearly mass chemotherapy in reducing human prevalence. Depending on the heterogeneity of prevalence within the population, targeted treatment of high prevalence groups, with lower overall coverage, can be more effective than mass treatment with higher overall coverage. Treatment confers a short term benefit only, with prevalence rising to endemic levels once chemotherapy programs are stopped; (2) depending on the relative contributions of bovines and humans, bovine treatment can benefit humans almost as much as human treatment. Like human treatment, bovine treatment confers a short-term benefit. A combination of human and bovine treatment will dramatically reduce human prevalence and maintains the reduction for a longer period of time than treatment of a single host, although human prevalence rises once treatment ceases; (3) assuming 75% coverage of bovines, a bovine vaccine which acts on worm fecundity must have about 75% efficacy to reduce the reproduction rate below one and ensure mid-term reduction and long-term elimination of the parasite. Such a vaccination program should be accompanied by an initial period of human treatment to instigate a short-term reduction in prevalence, following which the reduction is enhanced by vaccine effects; (4) if the bovine vaccine is only 45% efficacious (the level of current prototype vaccines) it will lower the endemic prevalence, but will not result in elimination. If it is accompanied by an initial period of human treatment and by a 45% improvement in human sanitation or a 30% reduction in contaminated water contact by humans, elimination is then possible.

New possible molluscicides from Calendula micrantha officinalis and Ammi majus. II. Molluscicidal, physiological, and egg-laying effects against Biomphalaria alexandrina and Bulinus truncatus.

In the present study, the effects of CuSo4 and crude extracts of the different parts of Calendula micrantha officinalis and Ammi majus, i. e., leaves, stems, roots, and flowers, on adult Biomphalaria alexandrina and Bulinus truncatus were investigated. Generally, leaves and flowers of both plants exhibited marked potency in killing the snail vectors of schistosomiasis. The recorded LC50 and LC90 values showed that C. officinalis was more toxic to both snails than A. majus, and B. truncatus are more sensitive to the extracts of both plants than B. alexandrina. Snails that are produced from snails previously exposed to low doses were more sensitive to the tested extracts, which may give primary indication of no possibility of inherited resistance. Moreover, prolonged exposure to the sublethal concentrations of A. majus have a definite lethal effect on the egg laying and longevity of both snails. Also, treatment with sublethal doses of both plants clearly inhibited the transaminase activity (ALAT, ASAT), diminished the total protein content, and increased markedly total lipid contents in the hemolymph of both snails.

The plant molluscicide Millettia thonningii (Leguminosae) as a topical antischistosomal agent.

The West African legume Millettia thonningii is used in Ghana as an anthelmintic and as a purgative agent. A chloroform extract of the seeds of Millettia thonningii which is known to be molluscicidal and cercaricidal was topically applied to mouse skin 2 and 24 h prior to exposure to Schistosoma mansoni cercariae. The presence of Millettia thonningii extract components on the surface of the skin appeared to be effective in preventing subsequent establishment of infection. The compound responsible for the activity is thought to be the isoflavonoid alpinumisoflavone.

Paddy field dermatitis in Assam: a cercarial dermatitis.

Rice field dermatitis is an occupational health problem in Assam. The afflicted paddy field workers develop exanthema on the exposed parts of their skin mainly legs and arms when they come in contact with water in rice fields. Itching sensations start after 30 minutes to 1 1/2 hours after initial exposure. After 6-12 hours there is intensely pruritic macular eruption and in a few cases secondary skin infection may also develop. The clinical course of the disease is suggestive of cercarial dermatitis. Numerous gastropod snails belonging to families Lymnaeidae, Bulinidae and Planorbidae were collected from paddy fields and were investigated for cercarial infection. It was found that planorbid snails were infected with animal schistosome cercariae. These cercariae were able to invade human skin and caused dermatitis in human volunteers after repeated exposure.