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.

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.

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.

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.

Control of schistosomiasis: report of a workshop.

Nineteen scientists, field workers, and representatives of funding agencies active in schistosomiasis research and control met in Bellagio, Italy in October 1977 to attempt to evaluate the effectiveness of current control methods and what might be accomplished with available technology. The deliberations included summaries of knowledge on the biology, transmission, and control of schistosomiasis and assessment of major control programs and methodologies. The groups concluded that in the major endemic areas considerable gains in control of schistosomiasis could be made with current technology. However, maintenance of control in most countries, and establishment of serious control programs in countries in which schistosomiasis is a less severe public health problem, would require development of less expensive modalities which would need little monitoring and possibly have benefits extending beyond schistosomiasis control.

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.

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.

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.

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.

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.

[The campaign against schistosomiasis]. / La lutte contre les schistosomiases.

Like other diseases linked to environment from where men look for supplies of goods, schistosomiases are difficult to control. Means of control are existing (mass treatment, selective treatment, with well tolerated drugs) but to insure the decrease of the prevalence over a long period of time, the strategies are sophisticated and often expensive. Therefore, today the objectives of schistosomiasis control are focused on the prevention and decrease of morbidity rather than on the decrease of transmission. Especially so when the economic, social and cultural levels do not permit to avoid the "pathogenic" behaviours.

[Field experinence of the molluscicide "Frescon" in the control of fascioliasis (author's transl)]. / Praktijkervaringen met het molluscicide "Frescon" voor de bestrijding van leverbotinfecties

The effectiveness of the molluscicide N-tritylmorpholine (Frescon, Shell) in the control of fascioliasis was tested in various field conditions. The effect was not only measured by the study of populations of L. truncatula but its use in prevention was also determined by turning tracer lambs out to grass in treated and control field. The studies showed that Frescon applied at the recommended dose rate is a reliable agent, even in the prevention of acute outbreaks of fascioliasis. The preventive effect was found to be most marked on treatment in the spring (preferable to single treatment during the summer), which is of particular importance in view of the fact that infections may occur in the southern Netherlands during the early grazing season.

[Biological aspects of the problem of opisthorchiasis]. / Biologicheskie aspekty problemy opistorkhoza.

The paper reports the latest data concerning genesis and structure of opisthorchiasis area; biology, ecology, position in the system and distribution of the first intermediate hosts of Opisthorchis felineus; peculiarities of infections with Opisthorchis of the first and second intermediate hosts. The methods of chemical control of mollusks, the first intermediate host of Opisthorchis, are discussed.

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.