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Memórias do Instituto Oswaldo Cruz
Fundação Oswaldo Cruz, Fiocruz
ISSN: 1678-8060 EISSN: 1678-8060
Vol. 90, Num. 2, 1995, pp. 285-288
Memorias Instituto Oswaldo Cruz, Vol. 90(2):285-288
mar./apr. 1995

Control of Schistosomiasis Transmission

Luiz C de S Dias, Oswaldo Marcal Jr*, Carmem M Glasser**

Departamento de Parasitologia, Instituto de Biologia, Universidade Estadual de Campinas, Caixa Postal 6109, 13083- 970 Campinas, SP, Brasil *Departamento de Biociencias, Universidade Federal de Uberlndia, Campus Umuarama, 38405-382 Uberlandia, MG, Brasil **Superintendencia de Controle de Endemias, Rua Paula Souza 166, 01027-000 S o Paulo, SP, Brasil

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Despite the sucess of control programmes, schistosomiasis is still a serious public health problem in the world. More than 70 countries where 200 million individuals are evaluated to be infected of a total 600 million at risk. Though there have been important local sucess in the control of transmission, globally the infection has increased. Economic constrains in developing countries, environmental changes associated with migration and water resources development have been blocking the progress. The main objective of schistosomiasis control is to achieve reduction of disease due to schistosomiasis. We discussed the control measures like: health education, diagnosis and chemotherapy, safe water supplies, sanitation and snail control. We emphasized the need to give priority to school-age children and the importance of integrating the measures of control into locally available systems of health care. The control of schistosomiasis is directly related to the capacity of the preventive health services of an endemic country. The strategy of control requires long-term commitment from the international to the local level.

Key words: schistosomiasis - control - transmission

Transmission of infection needs contact with water harbouring snail intermediate hosts in an area where sanitation is at a low level and there are infected individuals.

Basically, control of transmission involves measures like: reducing the risk of exposure to infected water and reducing the level of environmental contamination with schistosome eggs, and water contamination (Jordan & Webbe 1982).

The strategy for control of morbidity is effective (WHO 1993). The measures of control are health education, chemotherapy, water supply and sanitation, and snail control. The optimal balance between these measures will differ from one country to another.

Chemotherapy plays an important role in any control programme and will reduce morbitidy in the short term. Schistosomiasis transmission will depend on treatment can be applied and the epidemiological conditions.

The primary health care level is a prerequisite for achieving sustainable control.

According to WHO (1993) six factors should be observed when developing schistosomiasis control strategies: the felt needs of the population; the specie of Schistosoma present; the prevalence and intensity of infection, and the prevalence and severity of morbidity; epidemiological, ecological and environmental characteristics; the facilities of primary health care; technical support and the capacity for central and district management; the general coordination.

Control of schistosomiasis is not a static concept. The objective of control in the past has been considered as the interruption of transmission. Actually, the principal objective of schistosomiasis control is to achieve reduction of disease due to schistosomiasis.

The current trend is to integrate schistosomiasis control activities into the general health delivery system. There are many endemic areas where schistosomiasis is not yet recognized as an important public health problem and where it receives only a low priority for control.

The schistosomiasis control is feasible. The question is how it will be implemented within the available humam and economical resources of the endemic country. The control is related to the capacity of the preventive health services of an endemic area.

BASIS OF CONTROL

Epidemiology - Epidemiological characteristics must be considered in the assessment of a country's ability to undertake control. The characteristics have been defined by population based on epidemiological studies (Wilkins 1987); focal transmission is the role within an endemic area (Marcal Jr et al. 1991); only a small proportion of infected individuals have severe infections; the intensity of infection and prevalence are different from one locality to another; the prevalence and mean intensity of infection increase in parallel; the highest prevalence and intensity of infection are found in persons between 10 and 19 years old; water contact pattern; the presence of the disease in children or as sequelae in adults are directly proportional to the intensity of infection (Dias et al. 1992b).

Health education - Health education remains a high priority in control programmes (WHO 1985, Teesdale 1986). Community participation is vital in schistosomiasis programme (Ravaoalimalala 1986, Tanner et al. 1986). A health education approach can be developed in all endemic areas, emphasizing personal hygiene and the individual's role in controlling schistosomiasis. All control programmes require the knowledge, attitudes and practices of a community (Marcal Jr et al. 1993). Health education materials in local languages have been prepared for most programmes.

Snail control - Control of snail intermediate host is an effective means of reducing transmission of schistosomiasis, and may entail the use of molluscicides, plant molluscicides, biological agents and environmental management. The efficacy of snail control can be enhanced if combined with other methods of control. Chemical control remains the best method for the destruction of snail hosts. The focal use of molluscicides at epidemiologically important water contact sites has reduced the costs of snail control.

Diagnostic techniques - Parasitological, immunological (Dias et al. 1992a) and indirect techniques are available for diagnosis of schistosomiasis. The selection of any particular diagnostic technique in a large-scale programme is based on a series of choices. Quantitative diagnostic techniques have a unique role in the evaluation of schistosomiais control. Diagnosis for public health purposes requires that the technique is robust and simple using supplies and equipment that are readily available (WHO 1993). Development of diagnostic capacity is a goal of many health services and will contribute to overall efforts to control schistosomiasis.

Chemotherapy - According to Davis (1986) chemotherapy plays a leading role in the control of schistosomiasis, as in all other helminthic diseases. The primary objective of chemotherapy in schistosomiasis control should be the reduction and prevention of morbidity. Reduction of morbidity after treatment has now been validated with metrofonate, oxamniquine and praziquantel. Periodic treatment is now established as a central component of control. The appropriate drug treatment lowers worm burdens and prevents or reverses disease caused by all schistosome species. Several useful approaches are used for community-based treatment have been developed as: mass treatment, selective population chemotherapy and selected group treatment. Actually resistance and/or tolerance to antischistosomal drugs in current use are emergent problems that need special attention (Dias & Gon‡alves 1992, Drescher et al. 1993). In Brazil and Kenya were reported drug resistance and tolerance to oxamniquine and praziquantel.

Environmental management - Modifications through drainage, water management practices may be an effective means of eliminating the snail hosts of schistosomiasis. In irrigation development selection of the technique (i. e. surface or overhead drip) is the first decision with important health consequences. The siting of human settlements in and irrigation regions should be controlled (Brinkmann & Steingruber 1986, Mott 1987, WHO 1993).

Water supply and sanitation - The schistosomiasis in many parts of the world is directly related to human contact with water. The most transmission of schistomiais occurs during water contact for domestic and recreational purposes, and some water contact is occupational (Mar‡al Jr et al. 1991).

Water supply is central to the control. However a safe water supply by itself may not be sufficient to reduce schistosomiasis transmission and epidemiological data are also necessary (Mar‡al Jr et al. 1993).

It was conclude that a 10-20% reduction in the number of people with schistosomiasis (18-36 million cases) might be achieved as a result of providing safe public water supplies (De Wolfe Miller 1990).

However improvement of the water supply continues to be neglected as a measure for the control.

The construction and use of latrines should be encouraged to improve the standard of hygiene and to reduce the incidence of other faecal-borne disease as well (McJunkin 1983, Werler 1986).

Data management - The management of data aims to identify operational priorities and to target control activities on an epidemiological basis. In most control programmes some indices are needed, especially those related to the reduction of morbidity due to schistosomiasis in treated populations (Dixon 1986). The most indices are based on egg counts: prevalence of infection, prevalence of heavy infection, intensity of infection and incidence (Mott 1987). Microcomputers are taking their place in database management at central level and peripheral levels.

Training, organization and management - The training activities must be repeated periodically to update staff on new advances in technology and to rationalize the operational measures.

The organization and management of schistosomiasis control must be improved according to assure the efficacy of operations. It is an important sign of progress in national control programmes.

Cost of control - The cost of control remains high. Behind the costs there are a number of complex administrative and logistical issues which sole to every endemic country. The diminishing per capita expenditure on health in developing countries should be of concern to the international community.

Assessment of control - As human and economical resources in endemic countries become more restricted, assessment will become important. Changes from the initial prevalence and intensity of infection can evaluate the control operations. Evaluation technique based on limited sampling procedures may not represent the true situations. The university-based research groups and governmental agencies can be mutually evaluate the operational methodology as well as the impact of control.

Quality control, especially in the laboratory, is an important aspect of control.

Advances in general and biomedical technology have been proved to contribute effectively to schistosomiasis control. For example, microcomputers, ultrasound technology and health education through use of videotapes and television can reach endemic areas.

Though there have been important local sucess in the control of schistosomiasis (for example, in China, Brazil and Pemba Island, Tanzania), globally the infection has increased during the last decade (WHO 1993). This has been due partly to irrigation projects and partly to migration. Recent years have been a shift away from transmission control to the control of severe morbitidy. This shift was facilitated by the praziquantel, a safe and highly effective drug against all human schistosomiasis species.

The distribution of schistosomiasis is constantly changing. The migration of rural populations into urban areas continues unrelentingly. Today the schistosomiasis is as an important public health problem in large cities of endemic countries (WHO 1985).

There is a evident need for greater commitment to schistosomiasis control. However this may only be achieved by long-term efforts when the public health and socio-economic importance of the disease is better understood.

REFERENCES

Brinkmann A, Steingruber R 1986. Possible modifications in the construction of small dams to prevent the spread of schistosomiasis. Trop Med Parasitol 7: 199-201.

Davis A 1986. Recent advances in schistosomiasis. Quaterly J Med 58: 95-110.

De Wolfe Miller F 1990. Steering Committee for Cooperative Action for the International Drinking Water Supply and Sanitation Decade. Report on ID WSSD impact on schistosomiasis. Geneva. World Health Organization (unpublished document; available on request from Community Water Supply and Sanitation, World Health Organization, 1211, Geneva 27, Switzerland).

Dias LCS, Goncalves ER 1992 O Schistosoma mansoni diz n o as drogas. Ciencia Hoje 14: 22-25.

Dias LCS, Kanamura HY, Hoshino-Shimizu S, Glasser CM, Carvalho JF, Silva LC da 1992a. Fields trials for immunodiagnosis with reference to Schistosoma mansoni, p. 39-47. In NR Berquist Immunodiagnosis approaches in schistosomiasis. Proceedings of ICGEB/TDR Symposium, Shanghai, 1990. John Wiley & Sons, Chichester, England.

Dias LCS, Marcal Junior O, Glasser CM, Kanamura HY, Hotta LK 1992b. Control of schistosomiasis mansoni in a low transmission area (Controle da esquistossomose mans“nica em  rea de baixa transmiss o). Mem Inst Oswaldo Cruz 87 (Suppl.IV): 233-239.

Dixon HE 1986. Data management in schistosomiasis control programmes. Trop Med Parasitol 37: 209-215.

Drescher KM, Rogers E J, Bruce JI, Katz N, Dias LCS, Coles GC 1993. Response of drug resistant isolates of Schistosoma mansoni to antischistosomal agents. Mem Inst Oswaldo Cruz 88: 81-85.

Jordan P, Webbe G 1982. Control, p. 293-349. In P Jordan & G Webbe (eds) Schistosomiasis epidemiology, treatment and control, Willian Heinemann Books Ltd, London.

Marcal Junior O, Hotta LK, Patucci RMJ Glasser CM, Dias LCS 1993. Schistosomiasis mansoni in an area of low transmission. II. Risk factors for infection. Rev Inst Med trop S o Paulo 35: 331-335.

Marcal Junior O, Patucci RMJ, Dias LCS, Hotta LK Etzel A 1991. Schistosomiasis mansoni in an area of low transmission. I. Impact of control measures. Rev Inst Med trop S o Paulo 33: 83-90.

McJunkin FE 1993. Water and Human Health. Development Information Center, Agency for International Development, Washington, DC, 134pp.

Mott KE 1987. Schistosomiasis control, p. 431-450. In D Rollinson & AJG Simpson (eds) The biology of schistosomes from genes to latrines. Academic Press London.

Ravaoalomalala VA 1986. Community participation with PHC experience in Madagascar. Trop Med Parasitol 37: 170- 171.

Tanner M, Lwihula G K, Burnier E, DeSavigny D, Degr‚mont A 1986. Community participation within a primary health care programme. Trop Med Parasitol 37: 164-167.

Teesdale CH 1986. The role of health education to reduce transmission of schistosomiasis. Trop Med Parasitol 37: 184-185.

Werler C 1986. Costs of implementaion of water supply on in a schistosomiasis control programme in Mali. Trop Med Parasitol 37: 189-190.

Wilkings HA 1987. The epidemiology of schistosome infections in man, p. 379-397. In D Rollinson & AJG Simpson (eds), The biology of schistosomes from genes to latrines. Academic Press, London.

WHO 1985. The control of schistosomiasis. World Health Organization. Technical Report. Series 728, Geneva.

WHO 1993. The control of schistosomiasis: second report of the WHO Expert Committee. Technical Report. Series 830, Geneva.

Copyright 1995 Fundacao Oswaldo Cruz (Fiocruz)

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