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Memórias do Instituto Oswaldo Cruz
Fundação Oswaldo Cruz, Fiocruz
ISSN: 1678-8060 EISSN: 1678-8060
Vol. 91, Num. 5, 1996
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Mem Inst Oswaldo Cruz, Rio de Janeiro, Vol. 91(6),
Nov./Dec. 1996,
Control of Schistosomiasis Mansoni in Ravena (Sabara,
State of Minas Gerais, Brazil) through Water Supply and
Quadrennial Treatments
Pedro Coura-Filho/+, Roberto Sena Rocha, Simone da Silva
Lamartine, Marcio William C Farah*, Dilermando Fazito de
Resende**, Jose; Oswaldo Costa***, Naftale Katz
Laboratorio de Esquistossomose, Centro de Pesquisas Rene
Rachou-FIOCRUZ, Av. Augusto de Lima 1715, 30190-002 Belo
Horizonte, MG, Brasil *Fundacao Mineira de Arte-FUMA,
Universidade do Estado de Minas Gerais, Av. Amazonas 6252,
30530-000 Belo Horizonte, MG, Brasil **Fundacao Nacional de
Saude, Av. Brasil 2023, 30140-131 Belo Horizonte, MG, Brasil
***Departamento de Medicina Preventiva, Escola de Medicina
Veterinaria, UFMG, Belo Horizonte, MG, Brasil
Supported by FIOCRUZ/CNPq
+Corresponding author. Fax: +55-31-295.3115
Received 18 January 1996, Accepted 17 April 1996
Code Number: OC96119
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In this study, the results obtained in a control programme
of schistosomiasis in Ravena (Sabara, Minas Gerais) between
1980 and 1992 are evaluated. Control measures used in this
programme were: specific treatment of the people infected with
Schistosoma mansoni at four year-intervals (1980/84/88)
and the supply of tap water to 90% of the residences in 1980.
A significant reduction of the prevalence (36.7% to 11.5%,
p<=0.05) and of the intensity of the infection (228.9 eggs per
gram of feces (epg), s = 3.7 to 60.3 epg, s = 3.5, p<=0.05)
was observed. No cases of the severe form of the disease were
diagnosed in the area. Factors independently associated with
the infection were in 1980 daily sand extraction and the lack
of tap water in residences and in 1992 daily sand extraction
and fishing and weekly swimming. Concluding, the supply of tap
water together with quadrennial treatments significantly
diminished both the prevalence and intensity of the S.
mansoni infection, with the additional gain of persistent
low indices even after four-year intervals between the
treatments.
Key words: epidemiology of schistosomiasis - control -
measures: sanitation and treatments - Brazil
The relation between sanitation and the reduction of the
prevalence, egg counts and morbidity of schistosomiasis in
Brazil was studied by Barbosa et al. (1971), Lima e Costa et
al. (1994) and Coura-Filho (1994). Barbosa et al. (1971)
provided the residents of Pontezinha, PE, with cesspools, nine
community laundries and health education, for those who were
exposed to the infection with Schistosoma mansoni,
during seven years. At the end of this period they observed a
decrease of the prevalence from 30.0 to 3.8%. In three control
areas where no control measures were taken the prevalence, egg
loads and morbidity rates of the disease showed no significant
variation, although two areas seemed to present a tendency to
regression as well.
Lima e Costa et al. (1985) recorded that in the nucleus of
Comercinho, MG, residences provided with tap water presented
the lowest prevalence rates, compared to peripheral areas. In
1994, Lima e Costa et al., using a method of multiple
regression analysis, registered that the lack of supply of
water to residences was independently associated with the
presence of the hepatosplenic form of the disease.
In a review of studies about the determining factors in the
transmission of schistosomiasis obtained from seven endemic
areas in Brazil, Coura-Filho (1994) observed the absence of
specific treatment to be an indication of the infection with
S. mansoni in three of the four areas and the lack of
water supply to residences in three out of six.
Outside Brazil, Jordan et al. (1982) demonstrated the
association between the reduction of the transmission of
schistosomiasis and the supply of tap water as a control
measure, besides considering water supply to be the most
lasting measure for the control of the disease. It was also
calculated that this was the most expensive measure: U$ 4.1
per subject per year compared to a single treatment (U$
1.1).
Hunter et al. (1993) reviewed 16 studies carried out outside
Brazil, which indicated a reduction of the transmission of
waterborne diseases if water to the residences of the
population in an endemic area was supplied.
The influence of specific treatment on the regression of the
severe form of the disease is described in literature.
In this study the association between the supply of tap water
and quadrennial specific treatment of subjects to S.
mansoni infection is evaluated as a control measure of
schistosomiasis.
Materials And Methods
Studied area - Ravena is an area in the municipal
district of Sabara, MG, in Rio das Velhas basin, a
mountainous region characterized by gravelly sedimentation, 30
km north of Belo Horizonte. It has a population of
approximately 1,500 inhabitants that live in Ravena (centre)
and Lavapes (periphery of the district). It has an annual
migratory flux around 5%. The main commercial activity is the
growing of bananas, followed by dairy cattle farming and the
extraction of granite and sand for building construction. The
population of Ravena is provided with a local municipal
administration, a Municipal Health Center, two municipal
schools, a police station and two catholic churches. Civic
services include a telephone post, intermunicipal transport,
paved roads, electric light and potable water. 60% of the
streets are paved and 40% of the houses are served with a
sewerage system. In 1980 a watermain was installed serving 90%
of the residences of the district. At that time the prevalence
of schistosomiasis was 36.7%; the geometric mean of the number
of eggs per gram feces (epg) was 228.9 epg (s = 3.7) and no
cases of the hepatosplenic form of schistosomiasis were
reported (Coura-Filho et al. 1995).
In 1980, 1984, 1988 and 1992 parasitological stool exams of
the residents were performed followed by specific treatment of
the infected individuals with a single oral dose of
oxamniquine: 20 mg/kg bodyweight for children (younger than 15
years) and 15 mg/kg bodyweight for adults. The drug was
administered by a physician of the local health center. From
1989 onward the Municipal Health Center also started to record
the results of the parasitological stool exams performed in
the population on spontaneous demand outside Ravena.
Analysis of determinants - In order to evaluate
the clinical-epidemiological evolution of the S.
mansoni infection in the area the following qualities were
considered: prevalence, the intensity of the infection and the
clinical forms. To determine the prevalence, the arithmetic
mean of the S. mansoni egg counts found in two glass
slides prepared from one stool sample according to the Kato-
Katz method (Katz et al. 1972) was used. The intensity of the
infection was based on the geometric mean (G +/- s) of the
number of eggs per gram of feces of positive individuals. For
the identification of the clinical forms the classification
used by Pessoa and Barros (1953) with slight modifications was
applied: intestinal (I), hepatointestinal (HI) and
hepatosplenic (HS).
An analysis of the determinants of schistosomiasis was
carried out through the multiple regression analysis of the
factors (Campos-Filho & Franco 1989) considering the situation
before and 12 years after the start of the programme. In a
pre-tested questionnaire the following variables asked for
were: biological (sex, age), socio-cultural (place, reason and
frequency of contact with water of streams and rivers) and
socio-economic variables (profession, education, material
condition of the residence and the supply of tap water)
according to Coura-Filho (1994). The linear regression of the
prevalence per age group of the population during the period
was studied.
Results
The prevalence of the S. mansoni infection was
significantly reduced during the programme, from 36.7 to 11.5%
(p <= 0.01), though proved to be not significant in the age
group of 0-4 years, both in 1980 and 1992. Subjects in the age
group 10-29 years presented the highest prevalences during the
period of the programme (Table I). The drop in the prevalence
was significant both in the group of children as a whole (0-14
years) and in adults (>= 15 years) (Table II).
The examination of stool samples performed between 1989 and
1991 by the local health center on spontaneous demand showed
that 12 years after the installation of water supply to the
residences, around 70% of the examined individuals were
subjected to a worm infection, which was 87.4% before the
installation. Of the people examined 9.2, 5.4 and 4.2% were
excreting eggs of S. mansoni in 1989, 1990 and 1991,
respectively. The intensity of the infection of S.
mansoni, being initially 228.9 epg (s = 3.7), was also
significantly decreased in all age groups of the population
after the first treatment, staying continuously at a level
between 21.9 epg (s = 1.7) and 70.3 epg (s = 3.6) without
significant variation until 1992 (Table III) both among
children and adults living in the nucleus and in the periphery
of the district (Table IV).
An increase of the intestinal form (type I) from 81.3% to
97.9% of the total number of infected individuals was
observed. The prevalence of the cases of the hepato-intestinal
form dropped from 16.8% to 2.1% in 1992. Not a single case of
the hepatosplenic form of schistosomiasis was diagnosed in the
district.
The intensity of the infection among the subjects with the
intestinal form (240.42 epg, s = 4.82) was not significantly
different from the intensity among subjects with the hepato-
intestinal form (196.84 epg, s = 4.73) in 1980. However, 12
years later the latter group showed a significant lower
geometric mean of the epg (12.03 epg, s = 0.99) than the group
of the intestinal form (54.66 epg, s = 3.51).
Of the houses that initially were served with tap water
(90%), 12 years later 81% continued to be connected to the
watermains. The number of houses connected to the sewerage
system increased from 17.0 to 36.0% during the same period.
The multivariate analysis indicated that in the beginning of
the project the daily extraction of sand out of streams and
rivers in the region [(OR=3.44 (1.22-8.43)] and the lack of
tap water [(OR=2.47 (1.25-6.25)] were independently associated
with the infection. Twelve years later the factors
independently associated with the infection were: the daily
extraction of sand [(OR=2.07 (1.06-4.42)], daily fishing
[(OR=2.86 (1.78-7.22)] and weekly swimming [(OR=1.29 (1.40-
4.20)] (Table V).
Discussion
Evaluating the measures taken for the control of helminthoses
difficulties rise to define the ideal method of control. One
of the difficulties is the impossibility to compare the data
of distinct populations after intervention, even when socio-
economic and cultural conditions and used methods are similar.
Also in this study, designed to compare clinical-
epidemiological data before and after the implementation of
measures of control of schistosomiasis in Ravena, MG, the
possible changes in the way of life of the exposed population
were not taken into consideration.
During the period of study a significant reduction of the
prevalence, egg loads and morbidity rates was observed, but
unknown is to what extent each of the two measures, the
intradomiciliary supply of potable water and the specific
treatment, is responsible for this reduction.
In 1992 water supply to the residences was not independently
associated with the infection. At that time the determinants
for the transmission of schistosomiasis in the area were the
habits of swimming and fishing, mostly done in natural pools
and/or recreation clubs located close to the district. These
clubs were also visited by residents of neighbouring
settlements, mainly from the periphery of Belo Horizonte, not
submitted to any programme of control of schistosomiasis.
In areas where control programmes are undertaken a remainder
of the individuals continues to excrete eggs of S.
mansoni. Responsible for the continuation of the
transmission in the area is probably a group formed by
subjects with contraindications to treatment, non-examined or
non-diagnosed individuals, reinfected or non-cured patients
and migrants. Responsible for the maintenance of the highest
rates of prevalence among the residents of Lavapes seems to be
the absence of a sewerage system and the proximity of the
residences to the streams that are receiving excretements. The
multivariate analysis demonstrated that living in mentioned
place was independently associated with the transmission in
the district in the beginning of the programme.
Similar outcomes were described for the correlation of the
supply of tap water and the reduction of the infection in
Santa Lucia. In the latter area the initial control measure
consisted of specific treatment followed in a later stage by
the provision of tap water, which reduced the prevalence, egg
loads and morbidity rates of schistosomiasis even more. Still,
10% of the population continued to have water contact in
transmission sites, mainly because of swimming and fishing.
When analysing the determinants for the transmission of
schistosomiasis in seven endemic areas in Brazil Coura-Filho
(1994) also observed continuing water contact even after the
supply of tap water, resulting from leisure activities in
urban areas and from occupational (agricultural and domestic)
activities in rural areas.
Barbosa et al. (1971) and Lima e Costa et al. (1987) noticed
in Brazil a reduction of water contact of individuals when
supplied with tap water; Hunter et al. (1993) estimated this
specific contribution to the reduction of water contact to be
at least 20%, whereas Jordan et al. (1982) registered a
reduction up to 50% in the localities they studied.
The costs of the installation of tap water are generally
considered to be high, but the resulting impact on the control
of schistosomiasis is longer lasting and in Ravena the users
willingly participated financially in the operational costs of
the installation and distribution of tap water, like in Santa
Lucia. This mutual participation of local government and
residents gave way to the supply of tap water to 90% of the
residences in 1980, but fails in different, recently urbanized
areas in the peripheral zones of the big cities, where the
flux of settlement of new migrants exceeds the governmental
capacity to create an urban infra-structure (not only tap
water, but also sewerage system, light, public transport and
schooling).
In a settlement in Minas Gerais where yearly specific
treatment was combined with three-monthly applications of
molluscicides a significant drop of the prevalence was
recorded, but after interruption of the measures it tended to
revert to initial levels. The initial prevalence in the
endemic area of 43.5% decreased to 4.4% after the
implementation of control measures during 13 years, but
reverted to a prevalence of 19.6% three years after the
interruption of the programme Coura-Filho et al. (1994).
In conclusion, this study verifies that three quadrennial
specific treatments and the supply of tap water reduced the
prevalence and intensity of the infection with S.
mansoni permanently, both in the urban nucleus and in the
periphery of the district, consequently pointing out an
efficient model of control of schistosomiasis and its
implementation should therefore be stimulated in other endemic
areas in Brazil.
Acknowledgement
To Albert M Volloard for the suggestions about the
translation.
References
Barbosa FS, Pinto RF, Souza O 1971. Control of
schistosomiasis mansoni in a small town northeast Brazilian
community. Trans R Soc Trop Med Hyg 65: 206-213.
Campos Filho NBS, Franco EF 1989. A microcomputer programme
multiple logistic regression by unconditional and conditional
maximum likelihood methods. Am J Epidem 129:
439-444.
Coura-Filho P 1994. Use of risk pattern for schistosomiasis
in endemic areas in Brasil. Cad Saude Publ 10:
464-472.
Coura-Filho P, Rocha RS, Farah MW, Silva GC, Katz N 1994.
Identification of factors and groups at risk of infection with
Schistosoma mansoni: a strategy for the implementation
of control measures? Rev Inst Med Trop S Paulo
36: 245-253.
Coura-Filho P, Rocha RS, Farah MWC, Resende DF, Lamartine SS,
Carvalho OS, Katz N 1995. Determinantes ambientais e sociais
da esquistossomose mansoni em Ravena, Minas Gerais, Brasil.
Cad Saude Publ 11: 254-265.
Hunter JM, Rey L, Chu KY, Adekoluy-Jonh EO, Mott KE 1993.
Parasitic diseases in water resources development. The need
for intersectorial negotiation. WHO. Geneve.
Jordan P, Unrau GO, Bartholomeu RK, Cook JA, Grist E 1982.
Value of individual household water supplies in the
maintenance phase of a schistosomiasis control programme in
Saint Lucia, after chemotherapy. Bull WHO 60: 583-588.
Katz N, Chaves A, Pellegrino J 1972. Simple device for
quantitative stool thicksmear technique in schistosomiasis
mansoni. Rev Ins Med Trop S Paulo 14: 397-400.
Lima e Costa MFF, Rocha RS, Zicker F, Katz N 1985. Evolution
of schistosomiasis in an hyperendemic area of the Minas Gerais
State two cross-sectional studies. Rev Inst Med Trop S
Paulo 27: 229-292.
Lima e Costa MFF, Magalhaes MHA, Rocha RS, Antunes CMF, Katz
N 1987. Water contact patterns and socio-economic variables in
the epidemiology of schistosomiasis in an endemic area in
Brasil. Bull WHO 65: 57-66.
Lima e Costa MFF, Rocha RS, Magalhaes MHA, Katz N 1994. A
hierarchial pattern of analisis of the socio-economic
variables as well as the water contact patterns associated
with the hepatosplenic type of schistosomiasis. Cad Saude
Publ 10: 241-253.
Pessoa SB, Barros PR 1953. Observations on schistosomiasis
mansoni epidemiology in Sergipe state. Rev Med Cienc
13: 147-154.
TABLE I: Prevalence of infection by Schistosoma mansoni
in Ravena (Sabara, MG), according to age of the population
Age Years
group ---------------------------------------------------
1980 1984 1988 1992
--------- --------- ---------- ------------
I/E^a % I/E % I/E % I/E %
----------------------------------------------------------
0-4 9/110 8.3 0/0 - 0/0 - 3/92 3.3
5-9 38/145 26.2 8/54 14.0 0/13 0.0 3/138 2.2
10-14 69/146 47.3 23/66 34.8 12/53 22.6 23/170 13.5
15-19 87/135 64.4 23/74 31.0 13/51 25.4 38/117 32.5
20-29 77/167 46.1 39/114 34.2 25/58 43.1 34/199 17.1
>=30 86/295 29.2 32/197 16.2 17/234 7.2 34/453 7.5
Total 366/998 36.7 125/505 24.7 67/1169 16.4 135/1169 11.5
^a: infected/examined
Linear regression analysis along the time:
Age group b p
-------------------------------
0-4 -0.39+/-0.05 0.51
5-9 -2.79+/-1.76 0.26
10-14 -2.90+/-0.49 0.02
15-19 -2.58+/-1.78 0.28
20-29 -2.50+/-0.43 0.03
>=30 -1.88+/-0.44 0.05
Total -2.18+/-0.34 0.02
TABLE II: Prevalence of schistosomiasis mansoni in children
and adults in Ravena (Sabara, MG)
Ravena Lavapes
(centre) (periphery)
------------------------ ---------------------
Years Child^a Adult Child Adult
--------- --------- -------- --------
I/E^b % I/E % I/E % I/E %
-----------------------------------------------------
1980 83/344 24.1 207/534 38.8 33/56 58.9 43/63 68.2
1984 17/103 16.5 66/351 18.8 14/17 82.3 28/34 82.3
1988 6/80 7.5 45/283 15.9 6/14 42.8 10/32 31.3
1992 22/343 6.4 11/676 11.8 7/57 12.2 26/93 27.9
^a: <=14 years; ^b: infected/examined
Linear regression analysis along the time:
b p
Ravena: child(0-14 years) -0.57+/-0.12 0.04
(centre) adult(>=15 yeras) -0.39+/-0.13 0.02
Lavapes child -0.14+/-00.8 0.21
adult -0.16+/-0.08 0.19
TABLE III: Schistosoma mansoni infection intensity in
Ravena (Sabara, MG), according to age group
Age Years
----------------------------
group 1980 1984
-------------- -----------
N G+/-s^a N G+/-s
------------------------------------
0-4 9 102+/-2.6 - -
5-9 38 253+/-4.2 8 174.8+/-5.0
10-14 69 350+/-3.4 23 125.8+/-3.6
15-19 87 295.1+/-3.3 23 64.1+/-4.0
20-29 77 211.3+/-4.8 39 76.3+/-3.7
>=30 86 126.8+/-3.0 32 28.6+/-2.2
Total 366 228.9+/-3.7 125 72.7+/-3.2
Table III continued
Age Years
group -----------------------------
1988 1992
------------ -----------
N G+/-s N G+/-s
------------------------------------
0-4 - - 3 49.7+/-11.7
5-9 - - 3 21.9+/-1.7
10-14 12 113.0+/-4.0 23 57.0+/-3.3
15-19 13 80.4+/-3.9 38 70.3+/-3.6
20-29 25 67.4+/-3.7 34 70.0+/-3.2
>=30 17 29.7+/-2.4 34 46.3+/-3.3
Total 67 62.2+/-3.7 135 60.0+/-3.5
a: geometric mean +/- standard deviation
ANOVA from 1980 to 1992
Age group p
-------------------
0-4 0.04
5-9 0.03
10-14 0.02
15-19 0.02
20-29 0.00
>=30 0.03
Total 0.02
TABLE IV: Schistosoma mansoni infection intensity in
children and adults in Ravena (Sabara, MG)
Ravena (core)
-----------------------------
Years Child^a Adult
------------- -----------
N G+/-s^b N G+/-s
-----------------------------------
1980 83 257.0+/-3.5 207 200.0+/-3.5
1984 17 91.9+/-2.6 66 56.8+/-3.4
1988 6 79.1+/-2.1 45 48.3+/-3.6
1992 22 49.1+/-3.7 80 62.9+/-3.6
Table IV continued
Lavapes
----------------------------
Years Child Adult
----------- -----------
N G+/-s N G+/-s
----------------------------------
1980 33 365.4+/-3.9 43 228.1+/-3.9
1984 14 222.0+/-4.9 28 58.8+/-4.4
1988 6 167.8+/-6.2 10 94.4+/-3.1
1992 7 56.8+/-3.8 26 57.3+/-3.3
^a: child 0 - 14 years; ^b: geometric mean +/- standard
deviation
ANOVA from 1980 to 1992 p
--------------------------------------
Ravena: child (0-14 years) 0.04
(centre) adult (>=15 years) 0.03
Lavapes: child 0.02
adult 0.04
TABLE V: Schistosoma mansoni infection determinants in
Ravena (Sabara, MG) in 1980 and 1992
Risk factors 1980 1992
-------------------------------------------
OR^a p OR p
--------------------------------------------------------------
Professional (daily
sand extration) 3.44(1.22-8.43) 0.01 2.07(1.06-4.42) 0.05
Daily fishing NS^b 2.86(1.78-7.22) 0.02
Weekly swimming NS 1.29(1.40-4.20) 0.04
Residences without
potable water 2.47(1.25-6.23) 0.00 NS
^a: Odds Ratios; ^b: NS = non-significant to p <= 0.05
Copyright 1996 Fundacao Oswaldo Cruz
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