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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
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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
Code Number: OC95056
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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 &
Gonalves 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 (Maral 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 (Maral 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.
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Copyright 1995 Fundacao Oswaldo Cruz (Fiocruz)
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