‘< Preliminary study of urinary...
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Preliminary study of urinary schistosomiasis in a village in the delta of the
i
Senegal river basin, Senegal
p. Verlél, F. Stelma2, P. Desreumaux3, A. Dien$, 0. Diaw5, A. Kongs’, M. Niang6, S. Sow4, 1. Talla4, R. F.
Sturrock’, B. Gryseels” and A. Capron 3 ‘Co-operation of the Flemish Community of Belgium; 2University of Leiden, The
Netherlands; 31nstitut Pasteur, Lille, France; 4Centre de Santé de Richard-Tell, Senegal; 5~~~, Senegal; 6Health Region of
Saint-Louis, Senegal; 7London School of Hygiene and Tropical Medicine, L(ondon, UK
Abstract
Three years after the first cases of urinary schistosomiasis infection were reported in the village of Mbo-
diene, Senegal, Schistosoma haematobium eggs were found in 87% of the inhabitants of this village; 30% were
heavily infected (>50 eggs per 10 mL urine). The prevalence of infection was very high in a11 age groups,
but children showed more intense infections. No difference between sexes was found. In the special situ-
ation of a very high prevalence, test strips for proteinuria and haematuria are not very useful for the individ-
ual diagnosis of S. haematobium infection. Six and 12 weeks after treatment with a single dose of
praziquantel (40 mgikg), S. haematobium eggs were found in 25% and 30% of the treated subjects, respec-
tively. Bulinus globosus was identified as intermediate host, but lother snail vectors may also play a role. S.
mansoni eggs were found in 1% of the population. Both S. haematobium and S. mansoni are spreading in the
delta of the Senegal river.
Introduction
road N2. NO irrigation is planned in the Dieri, where
During the last 2 decades large irrigation projects have
only traditional agriculture is practised.
been introduced in the Senegal river basin, and 2 dams
Urinary schistosomiasis has been reported several
have been built. At Diama in Senegal, 40 km from the
times in the delta (CHAINE & MALEK, 1983; VER-
mouth of the river, the first dam became operational in
CRUYSSE et al., 1985). Reported prevalences were always
1986 to prevent salt water intrusion from the sea and a
very low, except in the focus of Lampsar, about 20 km
hydro-electric dam which regulates the water flow was
from the sea, where rice irrigation was introduced just
built in Manantali, Mali, and became operational in
after the second world war. It was suggested that the few
1989.
cases of schistosomiasis found in the rest of the delta
TN
MAURITANIA
Sencgal .*_
YmAFRICA0
0
scale : . .
15 km
Fig. 1. Map of the Senegal river delta, Senegal
The delta of the river in Senegal extends over 120 km
were acquired elsewhere ~CHAINE & MALEK, 1983).
inland from the sea, and is up to 50 km wide (Fig. 1). In
Higher prevalences, around lO%, were found in the
the north it is bordered by the main river, separating
Middle Valley and the Dieri (CHAINE & MALEK, 1983;
Senegal from Mauritania. In the south ii is roughly sep-
arated from the Dieri, the higher ground, by national
SARR, 1989).
Several studies have warned of a possible extension of
Address for correspondence: Dr. P. Verlé, Bijzondere Weg 4,
schistosomiasis in the Senegal river basin (VERCRUYSSE et
3360 Bierbeek, Belgium.
al., 1985; MALEK & CHAINE, 1989). Schistosoma mansoni
402
had never been reported before 1988 (TALLA et al.,
the urine was thoroughly mixed again and 10 mL were
1990). Since then, Richard-Toll, a town in the east of the
filtered with NytreP fïlters (WHO, 1983). The filters
delta, has been facing an epidemic of S. mansoni infec-
were stained with ninhydrin. Eggs were counted the
tion. In a period of 3 years, more than 60% of the popu-
same day; 10% of the slides were chosen at random and
lation has become heavily infected (TALLA et al.: 1992;
recounted within 24 hours (by P. V.) New NytreP filters
STELMA et al., 1993).
were used for every examination. For each individual,
The fïrst signs of a changing distribution of S. haema-
counts were expressed as eggs/lO mL, using the arith-
tobium infection in the delta were noticed in 1989 and are
metic mean when 2 urine samples were examined. Mean
reported in this paper. The preliminary results from a
group egg counts were calculated as geometric means of
survey in one village are described.
positive counts only. For 20 subjects the results were
based on a single urine specimen.
Study population
Stool examinarions consisted of duplicate 25 mg Kato
Mbodiene is a small village on the national road (N2)
slides (KAT% et al., 1972; POLDERMAN et al., 1985) from
between the sea (40 km) and Richard-TO11 (65 km). At
a single stool sample. The slides were examined at
the beginning of the 1980s an irrigation scheme became
Richard-TO& 24 to 48 h after preparation. Stool samples
operational nearby. The rice fïelds are separated from the
were obtained from 311 subjects. A random 10% sample
village by the road and by a small irrigation canal (1 m
of the slides was recounted. On the same day, a11 samples
wide) which is used for domestic and recreational pur-
reported to contain S. mansoni eggs were also re-exam-
poses. Drinking water is mostly obtained from the Lamp-
ined by one of the authors (F. S.).
sar river, a branch of the Senegal river in which trans-
Al1 subjects with S. haematobium infection were of-
mission of urinary schistosomiasis takes place in the
fered treatment with 40 mgikg of praziquantel, which
focus of Lampsar. The distance between Mbodiene and
245 accepted. Six and 12 weeks after treatment their
this focus is only about 20 km, but there is little com-
urine samples were collected and examined as described
munication between these 2 villages. Nearly 90% of the
before.
population of Mbodiene belong to the Ouoloff ethnie
group. In January 1989, villagers reported that several
Snail survey
children suffered from blood in their urine, a new phe-
In September 1991 (ar the end of the rainy season) and
nomenon in this village. A quick survey in Fehruary
Tulv 1992 (before the
”
,
first imDortant
L
rains) snails were
1989 revealed that 53157 children with a history of hae-
collected in the irrigation canal and Lampsar river, at
maturia had S. haematobium eggs in urine sediment (un-
sites where villagers had regular contact with the water.
published data). The villagers have been fully informed
Five observation points were chosen in each habitat.
of the results of the examinations and the transmission
cycle of the disease. Treatment, however, was at that
Results
time available only in the private pharmacies in Saint
Prevalence and intensity of infection
Louis at about US $25 per adult dose of praziquantel.
Data were obtained from 352 subjects (81%) of the
population, 160 male (77% of the male population) and
Methods
192 female (85% of the female population). Eighty sub-
Medical observation
jects were absent at the time of the collection of samples
Before the study, the whole population was informed
and 2 refused to participate. 78% (65182) of missing sub-
about its objectives and methods. A map was drawn and
jects were between 5 and 39 years, and 59% were male.
a11 houses were visited; 434 persons (208 males and 226
Overal!, 87% of the subjects were found to have S.
females) declared the village as their present permanent
haematobaum eggs in one or both urine samples and 30%
address.
had a mean egg couni of more than 50 eggsil0 mL urine.
The baseline survey took place in July 1992. Al1 vil-
The overall geometric mean was 17 eggsil0 mL in the in-
laçzers were invited to ioin the studv. Each subiect was
fected; 35% of the population had more than 50 eggsil0
&ed to provide at le& 2 urine simples on different
mL in one or both urine samples. No difference was
days and one stool sample. Collection containers were
found between sexes in prevalence or intensity of infec-
distributed between 10:00 and 14:O0. Examinations of
tion. Prevalence of infection with S. haematobium was
urine were carried out on the spot. Urine specimens were
very high (c. 8Oo/o or more) in a11 age groups (Fig. 2A),
thoroughly mixed and examined with a reagent strip
though slightly lower in the youngest and the oldest age
(Multistixm, Ames) within one hour of collection. The
groups (compared to the age group 10-14 years, P=O.O5
protein content in the urine was recorded as negative
and P=O.14, respectively). In children and Young adults
(<lO mg/100 mL of urine), trace (10-30 mg/100 mL),
(under 20 years of age) relatively more heavv infections
+(30-100 mg/100 mL), ++(10&300 mg/100 mL),
(over 50 eggsil0 mL urine) were found than m those 20
+++(300-2000 mg/100 mL) or ++++(>2000 mg1100
years or older (35% vs. 23%,P=O.O12). Of the 8 subjects
mL). Presence of blood or leucocytes in the urine was re-
reported to have been treated, 3 were negative, 3 had
corded as trace, +, + + or + + +. After this examination
light infections and 2 had heavy infections. When these
Fig. 2. Prevalence and egg COU~+ distribution ofSchistosomu haemarohium
in 10 mL urine samples from inhabitants of a recently infected focus (the village 01
Mbodiene) in the Senegal river basin, (A) before and (B) 6 and 12 weeks after treatment with a single dose of praziquantel:40 mpkg). Vertical lines indicate
95% confidence limits of prevalencc, GM = geometric mean egg count per 10 mL of urine from infected persans; in B, the hatched portion of rhe blocks in-
dicates the proportion with >50 eggsil0 mL.
403
Table 1. Validity of testing for haematuria and proteinuria with
with :a geometric mean egg Count of 3110 mL in the in-
dipsticks for the diagnosis of infection with S. haematobium in a
fected individuals. Adults (a 15 years old) were less com-
recently infected focus (the village of Mbodiene) in the Senegal river
monly infected 12 weeks after treatment than children
basin
(21% versus 38%, P=O.O25) (Fig. 2B).
Iktection of heavy infection
During the follow-up study after treatment, 13 of 41
Detecrion
of infection
:>50 eggs 10 mL urine)
subjects in whom S. haematobium eggs had not pre-
Threshold of posirivity
viouslv been detected were found to be infected. a11
zuaçe
a+
a-+
3trace
a+
a++
lightly.
Haematuria
Sensitivity “%:
6 7
51
4 0
91
81
73
Table 2. Numbers of snails, and numbers infected with furcocercous
Speclficity
i”‘u:
7 6
85
X9
51
6 8
7 9
cercariae, in two water bodies used by the villagers of Mbodiene,
Predictive value of
Senegal river basin
a positive test I”a)
9 5
9 6
9 6
44
5 2
6 0
Predictive value of
Lampsar
Irrigation canal
a negativr test ro,:
2 6
21
1x
9 3
8 9
X7
Sept. 1991 July 1992 Sept. 1991 July 1992
Proreinuria
Sensitivity ‘Vo:
55
32
17
7 9
55
35
Btomplralaria pfeifferi
0
3
0
0
Specificity ( %i
70
X7
9 2
6 0
8 2
9 3
Bulinu forskalii
0
z
1 5
0
Predictive value of
Bulinu globosus
0
(1)
0
364 (105)
a positive tesf ?%)
9 2
9 4
9 3
4 6
5 6
6X
Bulinu~ truncatw
0
0
0
78
l’rrdicrive value uf
a negative test W
19
16
15
8 7
X l
7 7
Bulinu senegalensis
0
0
140
2
“Numlxr infected with furcocercous cercariae in parentheses.
Threshold of positivitya
1
2
3
1
2
3
Snail survey
Haematuria and proteinuria
Sensitivity :“‘oJ
4 6
3 0
2 7
74
55
51
The results of the snail survey are shown in Table 2.
Specificity %!
8 5
91
91
71
x5
87
Known possible intermediate hosts for S. haematobium
Predictire valuc o f
were found in both habitats. Only Bulinus globosus was
a positive test (%I
9 5
9 6
9 5
5 2
6 0
6 2
shedding furcocercous cercariae; 106 of 366 (29%) were
I’rediçtive
value of
a negative test (“0,
19
17
16
8 7
8 2
XI
found to be infected. B. senegalensis, B. truncatus and B.
Haematuria or proteinuria
forskalii were also found in the irrigation canal near the
Sensitivity A:
7 6
6 9
5 6
9 6
91
85
village. A few Biomphaluria pfeifferi, intermediate host of
Speciiïcity 14’0)
61
7 2
X0
4 0
4 8
6 3
S. mansoni, were found in the Lampsar river.
Preduxive
value of
a pusitlvr test !‘!01
9 3
9 4
9 5
4 0
4 3
4 9
Predicrive
value o f
Discussion
a negatire test (“0)
2X
2 6
2 2
9 6
9 3
Y1
No previous data are available for the village of Mbo-
“Thresholds uf p«\\itiriry are mdlcatcd
thui: 1. haematuria Ltrace and or proteinuria
diene but it cari be assumed that until recently the situ-
.?xrace; 2. haematuria ~frxe and or pruteinurla a-; 3, haematuna
b+ and or
ation was not different from that in the rest of the delta,
proteinuria > +
i.e. thlat prevalence of infection with S. haematobium was
very 1.0~. MALEK & CHAINE (1989) suggested that the
treated subjects were excluded from the analysis, dis-
few C<ases of schistosomiasis seen were acquired outside
tribution of intensity and prevalence of infection did not
the delta, with the exception of the focus in Lampsar.
change.
According to villagers, bloody urine was unknown in the
In 4 subjects (2 males and 2 females), one single schis-
village before 1989. If true, then the local community
tosome egg with a lateral spine was found in one urine
had been exposed to S. haematobium for 4 years at the
sample, always among many S. haematobium eggs. No S.
most. Macroscopic haematuria detected by anamnesis
mansoni egg was found in the corresponding stool
has proved satisfactory for community diagnosis of S.
sample.
haematobium (ZIJLMANS et al., 1989; LENGELER et al.,
Sensitivity, specificity and predictive values of positive
1991). It is therefore most likely that transmission of S.
and negative results of testing with dipsticks for haema-
haematobium in this village is a new phenomenon. Never-
turia, proteinuria and combinations of the 2 are given in
theless, prevalence of this infection has reached very high
Table 1. Values for different tut-off levels for each test
levels (87%) and 30% of the subjects cari be considered as
and combination are calculated for 2 levels of infection
having a heavy infection (WHO, 1983). The prevalence
with S. haematobium. Values for leucocyturia were very
could even be higher if it were determined by examin-
similar to those for proteinuria. For a11 tests or combina-
ation of urine samples on more than 2 days (SAVIOLI et
tions of tests the sensitivity dropped with rising tut-off
al., 1990). Thirty-one percent of subjects in whom S.
level, while the specifïcity rose. When only heavy infec-
haemwtobium eggs had not previously been detected were
tions were considered, sensitivity rose while specifïcity
found to be infected during the follow-up study after
dropped. The predictive value of a positive test result
treatment, a11 with light infections. They might have
was generally high for the detection of infection, whereas
been already infected during the initial survey, but
the predictive value of a negative test was low. When
missed because of the day to day variability in egg excre-
only heavy infections were considered, the opposite was
tion (!$AVIOLI et al., 1990).
true for the predictive values.
The very high prevalence in a11 age groups, even the
S. haematobium eggs were found in stool samples of
youngest, is unusual. The equally high prevalence in the
461311 (15%) subjects. Two had no eggs in urine and 21
older age groups supports the likelihood that infection in
belonged to the heavily infected group (>50 eggsil0 mL
this population is recent (HAGAN, 1992).
urine). Four stool samples (1%) were found to contain S.
Haematuria and proteinuria detected by reagent strips
mansoni eggs. One subject had eggs of both S. haemata-
are considered to be highly specifïc and sensitive for S.
bium and S. mansoni in his stool sample.
haemutobium infection (MO~I- et al., 1985; SAVIOLI et al,.,
1990). However, evaluation of these indirect diagnostic
Follow-up after treatment
techniques is necessary in any specific situation, because
Six and 12 weeks after treatment, urine samples were
considerable differences have been reported between
obtained from, respectively, 170 (56%) and 173 (57%) of
count.ries (TANNER et al., 1983; MOTT et al., 1985). In
306 subjects found to be infected with S. haematobium in
our study the validity of test strrps as a diagnostic test for
the initial survey. At 6 weeks S. haematobium eggs were
S. haematobium infection was disappointing. Indeed, se-
found in 43/170 (25%) subjects with a geometric mean of
lecting subjects by chance would be likely to be better at
3 eggsil0 mL in the infected individuals. At 12 weeks S.
detecting infected persons than the use of test strips.
haematobium eggs were found in 52/173 (30%) subjects
However, haematuria testing detected 91% of heavy in-
--
404
-,
.--
406
Schistosomiasis in the Republic of Sao Tomé and Principe: human studies
J. AImedal, M. Corachanl, A. Sousa2, C. Ascaso3, J. M. Carvalho”, D. Rollinson4 and V. R. Southgatel’
‘StwiOn
de Medicina Tropical, Hospital Clinic, Barcelona, Spain; ‘Ministerio da Saude, Republica De Stio Tomé e Principe;
3Departamento de Bioestadistica, Universidad de Barcelona, Spain; 4Department of Zoology, The Natural Histoty Museum,
Cromwell Road, London, S W7 SBD, UK
Abstract
The only schistosome species found in stool specimens in the local population of the republic of Sao Tomé is
Schistosoma intercalatum. An initial survey of schoolchildren showed an overall prevalence of 10.9%, with
some schools reaching 29%. No S. haematobium egg was found in 782 urine specimens from the local popu-
!ation, although some were seen in the urine of Angolan soldiers stationed near the capital City. One village
m the endemic area, San Marçal, had an S. intercalatum prevalence of 43%, with 14 persons >40 years of age
harbouring severe infections. The transmission area is restricted to the north-east of the main island, where
5 foci apparently account for most of the infections. Seven cases recorded from Principe may be explained
by the fact that the children were attending school at Sao Tomé. Women carrying out domestic activities are
more at risk of contracting the infection because of longer periods of water contact than men. The morbidity
produced by the infection is restricted to splenomegaly and blood in the stools. High prevalences have been
found of Ascaris lumbricoides and Trichuris trichiura, and hookworm and Strongyloidesstercoralis
were also ob-
served. Praziquantel was well tolerated and appears to be a good tool for control purposes, although reinfec-
tion in the transmission area apparently occurs rapidly. Control strategies based on chemotherapy should
take into account an older age group as well as the schoolchildren. Focal mollusciciding and the introduction
of washing facilities may also have a role to_ play
.
in control. The possible recent introduction of the infection
to the island is discussed.
Introduction
Materials and Methods
Sao Tomé and Principe are 2 islands in the Gulî of
A survey was conducted in 1991 of 2930 schoolchild-
Guinea, approximately 245 and 217 km from the main-
ren (aged 5-15 years) from 26 schools in SAo Tomé for
land, with populations of 114 507 and 5637, respec-
intestinal helminths and faecal and urinary schistoso-
tively.
miasis. In addition, 100 pupils from the 2 main schools
The Atlas of the Global Distribution of Schistosomiasis
of the island of Prmcipe (Pagué district) were examined
(DOUMENGE et al., 1987) states that about 30% of the
by the Kato-Katz technique (KATZ et al., 1970); 3 slides
children in Sao Tomé were infected with Schistosoma hae-
were prepared from each stool sample. Seven hundred
matobium, but GRACIO (1988) found snails of the Bulinus
and eighty-two urine samples were examined by filtration
forskalii group and suggested that schistosomiasis could
as described by P~ERS (1976); they were checked for
be caused by S. haematobium, S. intercalatum and a hy-
gross haematuria and examined for haematuria and pro-
brid. However, a detailed survey of 1637 island children
teinuria with chemical reaeent strius (Hemastix@ and Al-
(ROMERO et al., 1989) showed the nresence of schisto-
bustix@, AMES laborator&). Urine ‘samples from 332
some eggs in stool samples only; thêy were identifïed as
schoolchildren infected with S. intercalatum were exam-
S. intercalatum. CORACHAN et al. (1988) described the
ined similarly in 1992.
first clinical case S. intercalatum infection in an immi-
An earlier indication of an S. intercalatum prevalence
grant from Sao Tomé.
of 11% (ROMERO et al., 1989) led us to choose a sample
In order to clarify the situation, a programme was de-
size of 3030 pupils from a total of 20 000 schoolchildren,
signed to provide information on the epidemiology and
based on the local census. Cluster sampling was used,
biology of schistosomiasis and to assess prospects for its
fïrst stratifying by districts and then by schools, propor-
future control in Sao Tomé. The present paper refers pri-
tionally to the number of children per school.
marily to the clinical and epidemiological aspects of the
A questionnaire relating to morbidity, water contact
study.
patterns and persona1 data was administered by 2 phys-
Human infections with S. intercalatum were described
icians and 2 fïeld workers. Al1 questions concerning
comprehensively by FISHER (1934) in Zaire. S. intercala-
symptoms related to their presencé in the last month:
tum is present in 5 countries, according to a World
The ohvsicians uhvsicallv examined a11 children. The
Health Organization survey (IAROTSKI & DAVIS,
que&o&aire had been p;eviously validated by repeated
1981~Chad? Central African Republic, Gabon, Came-
testing with local personnel. Al1 infected persons found
roon and Zalre-and subsequently reports reflecting a
during the fïrst survey (1991) were treated and re-exam-
wider distribution have appeared. Clinical infections in
ined at intervals of 3 and 12 months. In every survey, in-
immigrants from Equatorial Guinea were described by
fected persons were treated with 40 mgikg praziquantel
MAS et al. (1985) and CORACHAN et al. (1987a), and a
in a single dose. Mebendazole (100 mg112 h for 3 d) was
survey in that country revealed a focus of the infection in
given to treat other intestinal helminths. A new stool sur-
a district of Bata, the capital city (SIMARRO et al., 1989).
vey of 2856 children, which did not include the cases
Infections in Spanish tourists from Mali were described
found in 199 1, was conducted in 1992.
from a travellers’ clinic (CORACHAN et al., 1987b, 1992).
A survey for S. intercalatum was made in 1991-1992 of
The infection has also been reported from Nigeria
a11 752 inhabitants (470 females and 282 males) of the vil-
<AUENE etaZ.,1989).
lage of San Marçal in Sao TOI&. Urine samples froc
The objectives of the study in humans were to deter-
these 752 persons were also examined by filtration.
mine the prevalence of schistosomiasis in children of
In addition, a small sample of Angolan soldiers based
school age, to assess the morbidity and therapeutic re-
at the airport were examined for schistosomiasis infec-
sponse of the infection, to establish the pattern of water
tion.
contact in the endemic areas, and to monitor the dis-
tribution of infection in the whole population of a village
in an endemic area.
Results
Pnrnritnlnnt
404
fections, with a specificity of 76% for the presence of any
introduction of snails. Furthermore, irrigation culture
infection. Detection of proteinuria and leucocyturia was
has been applied irregularly until now, SO the canal is
less effective, and combinations of the tests did not result
often dry for several months. Also, the water level of the
in substantial improvement. In the special situation of
Lampsar river shows signifïcant fhtctuations. These are
very high prevalence, test strips did not prove to be very
unfavourable conditions for snails, especially for Biom-
useful for the diagnosis of individual S. haematobium in-
ahularia SDD. Pesticides and salinitv of the water mav also
fections.
limit the *inail populations. For example? Biomphalaria
A single schistosome egg with a lateral spine was found
pfeifferi was found in very high numbers m July 1990 in
in one urine sample from 4 subjects (2 males and 2 fe-
the Lampsar river at Ross-Bethio (unpublished data) but
males), always together with many S. haematobium eggs.
had disappeared some months later after a drop of the
Although no S. mansoni egg was found in the corre-
water level and an accidental influx of some sait water
sponding stool sample, these are likely to have been S.
from the ocean. Comparable numbers have not been seen
mansoni eggs. Considering these subjects as positive for
there since.
S. mansoni infection, the prevalence of intestinal schisto-
No B. pfeifferi was found in Mbodiene during this
somiasis rises from 1.3 to 2.6%. Atypical S. haematobium
study. However, it is possible that the subjects with S.
eggs have been observed in stool samples; S. intercala-
mansoni eggs were infected in the immediate surround-
tum, however, has never been found in the region but S.
ings of the village. In 1991, 4 of 88 Biomphalaria pfeifferi
bovis is highly endemic (VERCRUYSSE et al., 1985).
were found to be infected with furcocercariae in the
Although follow-up data are limited, a substantial
Lampsar river at Ross-Bethio, about 15 km from Mbo-
number of subjects was still infected 6 and 12 weeks after
diene (DEME, 1993) and in February 1993 (7 months
treatment. Finding eggs only 6 weeks after treatment
after the study) Biomphalaria have been found in the ir-
cannot be explained by reinfection, but may be due to
rigation canal near Mbodiene (J. Vercruysse, persona1
maturation of previously prepatent infections. The eff-
communication).
cacy of praziquantel is lower against immature stages of
At present, reinfection after treatment is almost inevit-
S. japonicum in hamsters (WEBBE & JAMES, 1977) and
able in ,tibodiene because no alternative water supply
those of S. mansoni in mice (SABAH et al., 1986). Adults
exists. Treatment and health education, water manage-
were signifïcantly less commonly infected 12 weeks after
ment and weed control of the small irrigation canal are
treatment than children. This could be explained by the
the onlv immediatelv available tools for control. These
hypothesis that praziquantel works better in a mature
Will nott~liminate snail hosts of S. haematobium but could
immune system or by there being a lower rate of reinfec-
be sufficrent to control Biomphalaria pfeifferi. Obviously
tion due to either different exposure patterns or im-
the whole delta is at risk of schistosomiasis; the dynamics
munity to reinfection in adults.
of snail populations Will eventually determine the dis-
Since 1989 the villagers have been informed about the
tribution. of the 2 endemic species. The increase and eco-
cause of the haematuria, and nurses responsible for
logical changes of the water bodies may also influence
medical tare in the area were advised to consider haema-
other vector borne diseases, such as malaria.
turia a suffcient indication for treatment with praziquan-
The exact time of the introduction of urinary schisto-
tel. Since 1991, this drug has been available in the health
somiasis in Mbodiene is not known but it appears to have
posts at about US $3 for one adult treatment. Neverthe-
taken place at about the same time as the outbreak of S.
less, although only one-eighth of the price in private
mansoni in Richard-TO11 (TALLA et al., 1990). The paral-
pharmacies, this high cost may have limited the number
le1 explosive evolution of 2 different forms of schistoso-
of treatments. Only 8 treatments (7 children) were given
miasis in the same region is striking. Transmission in
in the fïrst 6 months of 1992.
both foci appears to be similarly intense in non-immune
In 1989, shortly after this new schistosomiasis focus
populations of the same ethnie groups. Epidemiological
had been identifïed, a preliminary survey was carried out
and immunological studies in both locations are under
on some 150 primary schoolchildren from the villages of
way and these new, neighbouring foci provide a unique
Ndioungue, Ndiaye, Diagambal and Guomene, sur-
opportunity to study schistosomiasis in general.
rounding Mbodiene (unpublished data). This survey did
not indicate any other new foci of S. haematobium, al-
Acknowledgement
though the situation in those villages was quite similar to
We grarefully acknowledge the work of Ngary Sy, Abdoulaye
that in Mbodiene. There are now indications that urinary
Yague. Sohibou Guindo, Sevdou Tine and Mankeur Dion (the
schistosomiasis has spread to those villages as well: in-
technicians). Special thanks go to WARUA (ADRAO), Senegal,
creasing numbers of cases of haematuria have been re-
which provided excellent working conditions on the spot, and to
ported in routine health statistics from the area. In Mak-
ORS.rOLti fOr logistic SLIppOrt.
hana and Mbarigot, prevalences of up to 87% were found
This work was supported by the Flemish Community of Bel-
in children 5 to 14 years old
eium and bv the Science and Technoloev for Develoument oro-
(KONG~, 1993). S. haemato-
gramme of fhe Commission of the Euroyean Commuiities, ion-
bium had never been reported in these villages before;
tracts no. T52-0145NL and T53-CT91-0041 (University of
however they are located in the immediate surroundings
Leiden) and T52M-0079-F and T53CT91=0030
(Institut Pas-
of the village of Lampsar and are probably part of this
teur, Lille) and is associated with the ESPOIR programme for re-
old focus.
search ancl control of schistosomiasis in northern Senegal.
The available data suggest that Bulinus globosus i s a
main intermediate host in Mbodiene and, given the high
References
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Chaine, J. P. & Malek, E. A. (1983). Urinary schistosomiasis in
indicate great seasonal variability in snail populations. It
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Received 22 September 1993; accepted for publication 21
seels, B. (1993). Epidemiology of Schistosoma mansoni infec-
October 1993
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406
Schistosomiasis in the Republic of Sao Tomé and Principe: human studies
J. Almeda’, M. Corachanl, A. Sousa2, C. Ascaso3, J. M. Carvalho2, D. Rollinson4 and V. R. Southgate”
*Secci&z
de Medicina Tropical, Hospital Cl&ic, Barcelona, Spain; 2Ministerio da Saude, Republica De Süo Tomé e Principe;
3Departamento de Bioestadistica, Universidad de Barcelona, Spain; 4Department of Zoologv, The IVatural Histoy Museum,
Cromwell Road, London, S W7 SBD, UK
Abstract
The only schistosome species found in stool specimens in the local population of the republic of Sao Tomé is
Schistosoma intercalatum. An initial survey of schoolchildren showed an overall prevalence of 10.9%, with
some schools reaching 29%. No S. haematobium egg was found in 782 urine specimens from the local popu-
lation, although some were seen in the urine of Angolan soldiers stationed near the capital City. One village
in the endemic area, San Marçal, had an S. intercalatum prevalence of 43%, with 14 persons >40 years of age
harbouring severe infections. The transmission area is restricted to the north-east of the main island, where
5 foci apparently account for most of the infections. Seven cases recorded from Principe may be explained
by the fact that the children were attending school at Sao Tomé. Women carrying out domestic activities are
more at risk of contracting the infection because of longer periods of water contact than men. The morbidity
produced by the infection is restricted to splcnomegaly and blood in the stools. High prevalences have been
found of Ascaris lumbricoides and Trichuris trichiura, and hookworm and Strongyloidesstercoralis
were also ob-
served. Praziquantel was well tolerated and appears to be a good tool for control purposes, although reinfec-
tion in the transmission area apparently occurs rapidly. Control strategies based on chemotherapy should
take into account an older age group as well as the schoolchildren. Focal mollusciciding and the introduction
of washing facilities may also have a role to play in control. The possible recent introduction of the infection
to the island is discussed.
Introduction
Materials and Methods
Sao Tomé and Principe are 2 islands in the Gulf of
A survey was conducted in 1991 of 2930 schoolchild-
Guinea, approximately 245 and 2 17 km from the main-
ren (aged 5-15 years) from 26 schools in Sao Tomé for
land, with populations of 114 507 and 5637, respec-
intestinal helminths and faecal and urinary schistoso-
tively.
miasis. In addition, 100 pupils from the 2 main schools
The Atlas of the Global Distribution of Schistosomiasis
of the island of Princine Paeué district1 were examined
(DOUMENGE et al., 1987) states that about 30% of the
by the Kato-Katz techiiqbe ~KATZ et al:, 1970); 3 slides
children in Sao Tomé were infected with Schistosoma hae-
were prepared from each stool sample. Seven hundred
matobium, but GRACIO (1988) found snails of the Bulinus
and eighty-two urine samples were examined by filtration
forskalii group and suggested that schistosomiasis could
as described by PETER~ (1976); they were checked for
be caused by S. haematobium, S. intercalatum and a hy-
gross haematuria and examined for haematuria and pro-
brid. However, a detailed survey of 1637 island children
teinuria with chemical reagent strips (Hemastix@ and Al-
(ROMERO et al., 1989) showed the presence of schisto-
bustix@) , ,AMES laboratories). Urine samples from 332
some eggs in stool samples only; they were identified as
schoolchlldren infected with S. intercalatum were exam-
S. intercalatum. CORACHAN et al. (1988) described the
ined similarly in 1992.
fïrst clinical case S. intercalatum infection in an immi-
An earlier indication of an S. intercalatum prevalence
grant from Sao Tomé.
of 11% (ROMERO et al., 1989) led us to choose a sample
In order to clarify the situation, a programme was de-
size of 3030 pupils from a total of 20 000 schoolchildren,
signed to provide information on the epidemiology and
based on the local census. Cluster sampling was used,
biology of schistosomiasis and to assess prospects for its
first stratifying by districts and then by schools, propor-
future control in Sao Tomé. The present paper refers pri-
tionally to the number of children per school.
marily to the clinical and epidemiological aspects of the
A questionnaire relating to morbidity, water contact
study.
patterns and persona1 data was administered by 2 phys-
Human infections with S. intercalatum were described
icians and 2 fïeld workers. Al1 questions concernmg
comprehensively by FISHER (1934) in Zaire. S. intercala-
symptoms related to their presence in the last month.
tum -is present -in- 5 countries, according to a World
The physicians physically examined a11 children. The
Health Oreanization survev JIAROTSKI
& DAVIS.
questionnaire had been previouslv validated by repeated
1981 jChas? Central Afric& Ripublic, Gabon, Came:
testing with local personnel. Al1 infected persons found
roon and Zalre-and subsequently reports reflecting a
during the fïrst survey (1991) were treated and re-exam-
wider distribution have appeared. Clinical infections in
ined at intervals of 3 and 12 months. In every survey, in-
immigrants from Equatorial Guinea were descrihed by
fected persons were treated with 40 mg/kg praziquantel
MAS et al. (1985) and CORACHAN et al. (1987a), and a
in a single dose. Mebendazole (100 mg/12 h for 3 d) was
survey in that country revealed a focus of the infection in
given totreat other intestinal helminthi. A new stooi sur-
a district of Bata, the capital city (SIMARRO et al., 1989).
vey of 2856 children, which did not include the cases
Infections in Spanish tourists from Mali were described
found in 1991, was conducted in 1992.
from a travellers’ clinic (CORACHAN et al., 1987b, 1992).
A survey for S. intercalatum was made in 1991-1992 of
The infection has also been reported from Nigeria
a11 752 inhabitants (470 females and 282 males) of the vil-
(ARENE et al., 1989).
lage of San Marçai in Sao Tomé. Urine saiples from
The objectives of the study in humans were to deter-
these 752 persons were also examined by filtration.
mine the prevalence of schistosomiasis in children of
In addition, a small sample of Angolan soldiers based
school age, to assess the morbidity and therapeutic re-
at the airport were examined for schistosomiasis infec-
sponse of the infection, to establish the pattern of water
tion.
contact in the endemic areas, and to monitor the dis-
tribution of infection in the whole population of a village
Results
in an endemic area.
Parasitology
Address for correspondence: Dr J. Almeda, Seccibn de Me-
School survey. The only Schistosoma species found was
dicina Tropical, Hospital Clinic, Villarroel 170, 08036, Bar-
S. intercalatum; 332 children (10.9%) in the first survev,
celons, Spain.
and 333 (11.7%) in the second were infected, comprisi&
Preliminary study of urinary schistosomiasis in a village in the delta of the
i
Senegal river basin, Senegal
p. Verlél, F. Stelma2, P. Desreumaux3, A. Dien$, 0. Diaw5, A. Kongs’, M. Niang6, S. Sow4, 1. Talla4, R. F.
Sturrock’, B. Gryseels” and A. Capron 3 ‘Co-operation of the Flemish Community of Belgium; 2University of Leiden, The
Netherlands; 31nstitut Pasteur, Lille, France; 4Centre de Santé de Richard-Tell, Senegal; 5~~~, Senegal; 6Health Region of
Saint-Louis, Senegal; 7London School of Hygiene and Tropical Medicine, L(ondon, UK
Abstract
Three years after the first cases of urinary schistosomiasis infection were reported in the village of Mbo-
diene, Senegal, Schistosoma haematobium eggs were found in 87% of the inhabitants of this village; 30% were
heavily infected (>50 eggs per 10 mL urine). The prevalence of infection was very high in a11 age groups,
but children showed more intense infections. No difference between sexes was found. In the special situ-
ation of a very high prevalence, test strips for proteinuria and haematuria are not very useful for the individ-
ual diagnosis of S. haematobium infection. Six and 12 weeks after treatment with a single dose of
praziquantel (40 mgikg), S. haematobium eggs were found in 25% and 30% of the treated subjects, respec-
tively. Bulinus globosus was identified as intermediate host, but lother snail vectors may also play a role. S.
mansoni eggs were found in 1% of the population. Both S. haematobium and S. mansoni are spreading in the
delta of the Senegal river.
Introduction
road N2. NO irrigation is planned in the Dieri, where
During the last 2 decades large irrigation projects have
only traditional agriculture is practised.
been introduced in the Senegal river basin, and 2 dams
Urinary schistosomiasis has been reported several
have been built. At Diama in Senegal, 40 km from the
times in the delta (CHAINE & MALEK, 1983; VER-
mouth of the river, the first dam became operational in
CRUYSSE et al., 1985). Reported prevalences were always
1986 to prevent salt water intrusion from the sea and a
very low, except in the focus of Lampsar, about 20 km
hydro-electric dam which regulates the water flow was
from the sea, where rice irrigation was introduced just
built in Manantali, Mali, and became operational in
after the second world war. It was suggested that the few
1989.
cases of schistosomiasis found in the rest of the delta
TN
MAURITANIA
Sencgal .*_
YmAFRICA0
0
scale : . .
15 km
Fig. 1. Map of the Senegal river delta, Senegal
The delta of the river in Senegal extends over 120 km
were acquired elsewhere ~CHAINE & MALEK, 1983).
inland from the sea, and is up to 50 km wide (Fig. 1). In
Higher prevalences, around lO%, were found in the
the north it is bordered by the main river, separating
Middle Valley and the Dieri (CHAINE & MALEK, 1983;
Senegal from Mauritania. In the south ii is roughly sep-
arated from the Dieri, the higher ground, by national
SARR, 1989).
Several studies have warned of a possible extension of
Address for correspondence: Dr. P. Verlé, Bijzondere Weg 4,
schistosomiasis in the Senegal river basin (VERCRUYSSE et
3360 Bierbeek, Belgium.
al., 1985; MALEK & CHAINE, 1989). Schistosoma mansoni
402
had never been reported before 1988 (TALLA et al.,
the urine was thoroughly mixed again and 10 mL were
1990). Since then, Richard-Toll, a town in the east of the
filtered with NytreP fïlters (WHO, 1983). The filters
delta, has been facing an epidemic of S. mansoni infec-
were stained with ninhydrin. Eggs were counted the
tion. In a period of 3 years, more than 60% of the popu-
same day; 10% of the slides were chosen at random and
lation has become heavily infected (TALLA et al.: 1992;
recounted within 24 hours (by P. V.) New NytreP filters
STELMA et al., 1993).
were used for every examination. For each individual,
The fïrst signs of a changing distribution of S. haema-
counts were expressed as eggs/lO mL, using the arith-
tobium infection in the delta were noticed in 1989 and are
metic mean when 2 urine samples were examined. Mean
reported in this paper. The preliminary results from a
group egg counts were calculated as geometric means of
survey in one village are described.
positive counts only. For 20 subjects the results were
based on a single urine specimen.
Study population
Stool examinarions consisted of duplicate 25 mg Kato
Mbodiene is a small village on the national road (N2)
slides (KAT% et al., 1972; POLDERMAN et al., 1985) from
between the sea (40 km) and Richard-TO11 (65 km). At
a single stool sample. The slides were examined at
the beginning of the 1980s an irrigation scheme became
Richard-TO& 24 to 48 h after preparation. Stool samples
operational nearby. The rice fïelds are separated from the
were obtained from 311 subjects. A random 10% sample
village by the road and by a small irrigation canal (1 m
of the slides was recounted. On the same day, a11 samples
wide) which is used for domestic and recreational pur-
reported to contain S. mansoni eggs were also re-exam-
poses. Drinking water is mostly obtained from the Lamp-
ined by one of the authors (F. S.).
sar river, a branch of the Senegal river in which trans-
Al1 subjects with S. haematobium infection were of-
mission of urinary schistosomiasis takes place in the
fered treatment with 40 mgikg of praziquantel, which
focus of Lampsar. The distance between Mbodiene and
245 accepted. Six and 12 weeks after treatment their
this focus is only about 20 km, but there is little com-
urine samples were collected and examined as described
munication between these 2 villages. Nearly 90% of the
before.
population of Mbodiene belong to the Ouoloff ethnie
group. In January 1989, villagers reported that several
Snail survey
children suffered from blood in their urine, a new phe-
In September 1991 (ar the end of the rainy season) and
nomenon in this village. A quick survey in Fehruary
Tulv 1992 (before the
”
,
first imDortant
L
rains) snails were
1989 revealed that 53157 children with a history of hae-
collected in the irrigation canal and Lampsar river, at
maturia had S. haematobium eggs in urine sediment (un-
sites where villagers had regular contact with the water.
published data). The villagers have been fully informed
Five observation points were chosen in each habitat.
of the results of the examinations and the transmission
cycle of the disease. Treatment, however, was at that
Results
time available only in the private pharmacies in Saint
Prevalence and intensity of infection
Louis at about US $25 per adult dose of praziquantel.
Data were obtained from 352 subjects (81%) of the
population, 160 male (77% of the male population) and
Methods
192 female (85% of the female population). Eighty sub-
Medical observation
jects were absent at the time of the collection of samples
Before the study, the whole population was informed
and 2 refused to participate. 78% (65182) of missing sub-
about its objectives and methods. A map was drawn and
jects were between 5 and 39 years, and 59% were male.
a11 houses were visited; 434 persons (208 males and 226
Overal!, 87% of the subjects were found to have S.
females) declared the village as their present permanent
haematobaum eggs in one or both urine samples and 30%
address.
had a mean egg couni of more than 50 eggsil0 mL urine.
The baseline survey took place in July 1992. Al1 vil-
The overall geometric mean was 17 eggsil0 mL in the in-
laçzers were invited to ioin the studv. Each subiect was
fected; 35% of the population had more than 50 eggsil0
&ed to provide at le& 2 urine simples on different
mL in one or both urine samples. No difference was
days and one stool sample. Collection containers were
found between sexes in prevalence or intensity of infec-
distributed between 10:00 and 14:O0. Examinations of
tion. Prevalence of infection with S. haematobium was
urine were carried out on the spot. Urine specimens were
very high (c. 8Oo/o or more) in a11 age groups (Fig. 2A),
thoroughly mixed and examined with a reagent strip
though slightly lower in the youngest and the oldest age
(Multistixm, Ames) within one hour of collection. The
groups (compared to the age group 10-14 years, P=O.O5
protein content in the urine was recorded as negative
and P=O.14, respectively). In children and Young adults
(<lO mg/100 mL of urine), trace (10-30 mg/100 mL),
(under 20 years of age) relatively more heavv infections
+(30-100 mg/100 mL), ++(10&300 mg/100 mL),
(over 50 eggsil0 mL urine) were found than m those 20
+++(300-2000 mg/100 mL) or ++++(>2000 mg1100
years or older (35% vs. 23%,P=O.O12). Of the 8 subjects
mL). Presence of blood or leucocytes in the urine was re-
reported to have been treated, 3 were negative, 3 had
corded as trace, +, + + or + + +. After this examination
light infections and 2 had heavy infections. When these
Fig. 2. Prevalence and egg COU~+ distribution ofSchistosomu haemarohium
in 10 mL urine samples from inhabitants of a recently infected focus (the village 01
Mbodiene) in the Senegal river basin, (A) before and (B) 6 and 12 weeks after treatment with a single dose of praziquantel:40 mpkg). Vertical lines indicate
95% confidence limits of prevalencc, GM = geometric mean egg count per 10 mL of urine from infected persans; in B, the hatched portion of rhe blocks in-
dicates the proportion with >50 eggsil0 mL.
403
Table 1. Validity of testing for haematuria and proteinuria with
with :a geometric mean egg Count of 3110 mL in the in-
dipsticks for the diagnosis of infection with S. haematobium in a
fected individuals. Adults (a 15 years old) were less com-
recently infected focus (the village of Mbodiene) in the Senegal river
monly infected 12 weeks after treatment than children
basin
(21% versus 38%, P=O.O25) (Fig. 2B).
Iktection of heavy infection
During the follow-up study after treatment, 13 of 41
Detecrion
of infection
:>50 eggs 10 mL urine)
subjects in whom S. haematobium eggs had not pre-
Threshold of posirivity
viouslv been detected were found to be infected. a11
zuaçe
a+
a-+
3trace
a+
a++
lightly.
Haematuria
Sensitivity “%:
6 7
51
4 0
91
81
73
Table 2. Numbers of snails, and numbers infected with furcocercous
Speclficity
i”‘u:
7 6
85
X9
51
6 8
7 9
cercariae, in two water bodies used by the villagers of Mbodiene,
Predictive value of
Senegal river basin
a positive test I”a)
9 5
9 6
9 6
44
5 2
6 0
Predictive value of
Lampsar
Irrigation canal
a negativr test ro,:
2 6
21
1x
9 3
8 9
X7
Sept. 1991 July 1992 Sept. 1991 July 1992
Proreinuria
Sensitivity ‘Vo:
55
32
17
7 9
55
35
Btomplralaria pfeifferi
0
3
0
0
Specificity ( %i
70
X7
9 2
6 0
8 2
9 3
Bulinu forskalii
0
z
1 5
0
Predictive value of
Bulinu globosus
0
(1)
0
364 (105)
a positive tesf ?%)
9 2
9 4
9 3
4 6
5 6
6X
Bulinu~ truncatw
0
0
0
78
l’rrdicrive value uf
a negative test W
19
16
15
8 7
X l
7 7
Bulinu senegalensis
0
0
140
2
“Numlxr infected with furcocercous cercariae in parentheses.
Threshold of positivitya
1
2
3
1
2
3
Snail survey
Haematuria and proteinuria
Sensitivity :“‘oJ
4 6
3 0
2 7
74
55
51
The results of the snail survey are shown in Table 2.
Specificity %!
8 5
91
91
71
x5
87
Known possible intermediate hosts for S. haematobium
Predictire valuc o f
were found in both habitats. Only Bulinus globosus was
a positive test (%I
9 5
9 6
9 5
5 2
6 0
6 2
shedding furcocercous cercariae; 106 of 366 (29%) were
I’rediçtive
value of
a negative test (“0,
19
17
16
8 7
8 2
XI
found to be infected. B. senegalensis, B. truncatus and B.
Haematuria or proteinuria
forskalii were also found in the irrigation canal near the
Sensitivity A:
7 6
6 9
5 6
9 6
91
85
village. A few Biomphaluria pfeifferi, intermediate host of
Speciiïcity 14’0)
61
7 2
X0
4 0
4 8
6 3
S. mansoni, were found in the Lampsar river.
Preduxive
value of
a pusitlvr test !‘!01
9 3
9 4
9 5
4 0
4 3
4 9
Predicrive
value o f
Discussion
a negatire test (“0)
2X
2 6
2 2
9 6
9 3
Y1
No previous data are available for the village of Mbo-
“Thresholds uf p«\\itiriry are mdlcatcd
thui: 1. haematuria Ltrace and or proteinuria
diene but it cari be assumed that until recently the situ-
.?xrace; 2. haematuria ~frxe and or pruteinurla a-; 3, haematuna
b+ and or
ation was not different from that in the rest of the delta,
proteinuria > +
i.e. thlat prevalence of infection with S. haematobium was
very 1.0~. MALEK & CHAINE (1989) suggested that the
treated subjects were excluded from the analysis, dis-
few C<ases of schistosomiasis seen were acquired outside
tribution of intensity and prevalence of infection did not
the delta, with the exception of the focus in Lampsar.
change.
According to villagers, bloody urine was unknown in the
In 4 subjects (2 males and 2 females), one single schis-
village before 1989. If true, then the local community
tosome egg with a lateral spine was found in one urine
had been exposed to S. haematobium for 4 years at the
sample, always among many S. haematobium eggs. No S.
most. Macroscopic haematuria detected by anamnesis
mansoni egg was found in the corresponding stool
has proved satisfactory for community diagnosis of S.
sample.
haematobium (ZIJLMANS et al., 1989; LENGELER et al.,
Sensitivity, specificity and predictive values of positive
1991). It is therefore most likely that transmission of S.
and negative results of testing with dipsticks for haema-
haematobium in this village is a new phenomenon. Never-
turia, proteinuria and combinations of the 2 are given in
theless, prevalence of this infection has reached very high
Table 1. Values for different tut-off levels for each test
levels (87%) and 30% of the subjects cari be considered as
and combination are calculated for 2 levels of infection
having a heavy infection (WHO, 1983). The prevalence
with S. haematobium. Values for leucocyturia were very
could even be higher if it were determined by examin-
similar to those for proteinuria. For a11 tests or combina-
ation of urine samples on more than 2 days (SAVIOLI et
tions of tests the sensitivity dropped with rising tut-off
al., 1990). Thirty-one percent of subjects in whom S.
level, while the specifïcity rose. When only heavy infec-
haemwtobium eggs had not previously been detected were
tions were considered, sensitivity rose while specifïcity
found to be infected during the follow-up study after
dropped. The predictive value of a positive test result
treatment, a11 with light infections. They might have
was generally high for the detection of infection, whereas
been already infected during the initial survey, but
the predictive value of a negative test was low. When
missed because of the day to day variability in egg excre-
only heavy infections were considered, the opposite was
tion (!$AVIOLI et al., 1990).
true for the predictive values.
The very high prevalence in a11 age groups, even the
S. haematobium eggs were found in stool samples of
youngest, is unusual. The equally high prevalence in the
461311 (15%) subjects. Two had no eggs in urine and 21
older age groups supports the likelihood that infection in
belonged to the heavily infected group (>50 eggsil0 mL
this population is recent (HAGAN, 1992).
urine). Four stool samples (1%) were found to contain S.
Haematuria and proteinuria detected by reagent strips
mansoni eggs. One subject had eggs of both S. haemata-
are considered to be highly specifïc and sensitive for S.
bium and S. mansoni in his stool sample.
haemutobium infection (MO~I- et al., 1985; SAVIOLI et al,.,
1990). However, evaluation of these indirect diagnostic
Follow-up after treatment
techniques is necessary in any specific situation, because
Six and 12 weeks after treatment, urine samples were
considerable differences have been reported between
obtained from, respectively, 170 (56%) and 173 (57%) of
count.ries (TANNER et al., 1983; MOTT et al., 1985). In
306 subjects found to be infected with S. haematobium in
our study the validity of test strrps as a diagnostic test for
the initial survey. At 6 weeks S. haematobium eggs were
S. haematobium infection was disappointing. Indeed, se-
found in 43/170 (25%) subjects with a geometric mean of
lecting subjects by chance would be likely to be better at
3 eggsil0 mL in the infected individuals. At 12 weeks S.
detecting infected persons than the use of test strips.
haematobium eggs were found in 52/173 (30%) subjects
However, haematuria testing detected 91% of heavy in-
--
404
-,
.--
406
Schistosomiasis in the Republic of Sao Tomé and Principe: human studies
J. AImedal, M. Corachanl, A. Sousa2, C. Ascaso3, J. M. Carvalho”, D. Rollinson4 and V. R. Southgatel’
‘StwiOn
de Medicina Tropical, Hospital Clinic, Barcelona, Spain; ‘Ministerio da Saude, Republica De Stio Tomé e Principe;
3Departamento de Bioestadistica, Universidad de Barcelona, Spain; 4Department of Zoology, The Natural Histoty Museum,
Cromwell Road, London, S W7 SBD, UK
Abstract
The only schistosome species found in stool specimens in the local population of the republic of Sao Tomé is
Schistosoma intercalatum. An initial survey of schoolchildren showed an overall prevalence of 10.9%, with
some schools reaching 29%. No S. haematobium egg was found in 782 urine specimens from the local popu-
!ation, although some were seen in the urine of Angolan soldiers stationed near the capital City. One village
m the endemic area, San Marçal, had an S. intercalatum prevalence of 43%, with 14 persons >40 years of age
harbouring severe infections. The transmission area is restricted to the north-east of the main island, where
5 foci apparently account for most of the infections. Seven cases recorded from Principe may be explained
by the fact that the children were attending school at Sao Tomé. Women carrying out domestic activities are
more at risk of contracting the infection because of longer periods of water contact than men. The morbidity
produced by the infection is restricted to splenomegaly and blood in the stools. High prevalences have been
found of Ascaris lumbricoides and Trichuris trichiura, and hookworm and Strongyloidesstercoralis
were also ob-
served. Praziquantel was well tolerated and appears to be a good tool for control purposes, although reinfec-
tion in the transmission area apparently occurs rapidly. Control strategies based on chemotherapy should
take into account an older age group as well as the schoolchildren. Focal mollusciciding and the introduction
of washing facilities may also have a role to_ play
.
in control. The possible recent introduction of the infection
to the island is discussed.
Introduction
Materials and Methods
Sao Tomé and Principe are 2 islands in the Gulî of
A survey was conducted in 1991 of 2930 schoolchild-
Guinea, approximately 245 and 217 km from the main-
ren (aged 5-15 years) from 26 schools in SAo Tomé for
land, with populations of 114 507 and 5637, respec-
intestinal helminths and faecal and urinary schistoso-
tively.
miasis. In addition, 100 pupils from the 2 main schools
The Atlas of the Global Distribution of Schistosomiasis
of the island of Prmcipe (Pagué district) were examined
(DOUMENGE et al., 1987) states that about 30% of the
by the Kato-Katz technique (KATZ et al., 1970); 3 slides
children in Sao Tomé were infected with Schistosoma hae-
were prepared from each stool sample. Seven hundred
matobium, but GRACIO (1988) found snails of the Bulinus
and eighty-two urine samples were examined by filtration
forskalii group and suggested that schistosomiasis could
as described by P~ERS (1976); they were checked for
be caused by S. haematobium, S. intercalatum and a hy-
gross haematuria and examined for haematuria and pro-
brid. However, a detailed survey of 1637 island children
teinuria with chemical reaeent strius (Hemastix@ and Al-
(ROMERO et al., 1989) showed the nresence of schisto-
bustix@, AMES laborator&). Urine ‘samples from 332
some eggs in stool samples only; thêy were identifïed as
schoolchildren infected with S. intercalatum were exam-
S. intercalatum. CORACHAN et al. (1988) described the
ined similarly in 1992.
first clinical case S. intercalatum infection in an immi-
An earlier indication of an S. intercalatum prevalence
grant from Sao Tomé.
of 11% (ROMERO et al., 1989) led us to choose a sample
In order to clarify the situation, a programme was de-
size of 3030 pupils from a total of 20 000 schoolchildren,
signed to provide information on the epidemiology and
based on the local census. Cluster sampling was used,
biology of schistosomiasis and to assess prospects for its
fïrst stratifying by districts and then by schools, propor-
future control in Sao Tomé. The present paper refers pri-
tionally to the number of children per school.
marily to the clinical and epidemiological aspects of the
A questionnaire relating to morbidity, water contact
study.
patterns and persona1 data was administered by 2 phys-
Human infections with S. intercalatum were described
icians and 2 fïeld workers. Al1 questions concerning
comprehensively by FISHER (1934) in Zaire. S. intercala-
symptoms related to their presencé in the last month:
tum is present in 5 countries, according to a World
The ohvsicians uhvsicallv examined a11 children. The
Health Organization survey (IAROTSKI & DAVIS,
que&o&aire had been p;eviously validated by repeated
1981~Chad? Central African Republic, Gabon, Came-
testing with local personnel. Al1 infected persons found
roon and Zalre-and subsequently reports reflecting a
during the fïrst survey (1991) were treated and re-exam-
wider distribution have appeared. Clinical infections in
ined at intervals of 3 and 12 months. In every survey, in-
immigrants from Equatorial Guinea were described by
fected persons were treated with 40 mgikg praziquantel
MAS et al. (1985) and CORACHAN et al. (1987a), and a
in a single dose. Mebendazole (100 mg112 h for 3 d) was
survey in that country revealed a focus of the infection in
given to treat other intestinal helminths. A new stool sur-
a district of Bata, the capital city (SIMARRO et al., 1989).
vey of 2856 children, which did not include the cases
Infections in Spanish tourists from Mali were described
found in 199 1, was conducted in 1992.
from a travellers’ clinic (CORACHAN et al., 1987b, 1992).
A survey for S. intercalatum was made in 1991-1992 of
The infection has also been reported from Nigeria
a11 752 inhabitants (470 females and 282 males) of the vil-
<AUENE etaZ.,1989).
lage of San Marçal in Sao TOI&. Urine samples froc
The objectives of the study in humans were to deter-
these 752 persons were also examined by filtration.
mine the prevalence of schistosomiasis in children of
In addition, a small sample of Angolan soldiers based
school age, to assess the morbidity and therapeutic re-
at the airport were examined for schistosomiasis infec-
sponse of the infection, to establish the pattern of water
tion.
contact in the endemic areas, and to monitor the dis-
tribution of infection in the whole population of a village
in an endemic area.
Results
Pnrnritnlnnt
404
fections, with a specificity of 76% for the presence of any
introduction of snails. Furthermore, irrigation culture
infection. Detection of proteinuria and leucocyturia was
has been applied irregularly until now, SO the canal is
less effective, and combinations of the tests did not result
often dry for several months. Also, the water level of the
in substantial improvement. In the special situation of
Lampsar river shows signifïcant fhtctuations. These are
very high prevalence, test strips did not prove to be very
unfavourable conditions for snails, especially for Biom-
useful for the diagnosis of individual S. haematobium in-
ahularia SDD. Pesticides and salinitv of the water mav also
fections.
limit the *inail populations. For example? Biomphalaria
A single schistosome egg with a lateral spine was found
pfeifferi was found in very high numbers m July 1990 in
in one urine sample from 4 subjects (2 males and 2 fe-
the Lampsar river at Ross-Bethio (unpublished data) but
males), always together with many S. haematobium eggs.
had disappeared some months later after a drop of the
Although no S. mansoni egg was found in the corre-
water level and an accidental influx of some sait water
sponding stool sample, these are likely to have been S.
from the ocean. Comparable numbers have not been seen
mansoni eggs. Considering these subjects as positive for
there since.
S. mansoni infection, the prevalence of intestinal schisto-
No B. pfeifferi was found in Mbodiene during this
somiasis rises from 1.3 to 2.6%. Atypical S. haematobium
study. However, it is possible that the subjects with S.
eggs have been observed in stool samples; S. intercala-
mansoni eggs were infected in the immediate surround-
tum, however, has never been found in the region but S.
ings of the village. In 1991, 4 of 88 Biomphalaria pfeifferi
bovis is highly endemic (VERCRUYSSE et al., 1985).
were found to be infected with furcocercariae in the
Although follow-up data are limited, a substantial
Lampsar river at Ross-Bethio, about 15 km from Mbo-
number of subjects was still infected 6 and 12 weeks after
diene (DEME, 1993) and in February 1993 (7 months
treatment. Finding eggs only 6 weeks after treatment
after the study) Biomphalaria have been found in the ir-
cannot be explained by reinfection, but may be due to
rigation canal near Mbodiene (J. Vercruysse, persona1
maturation of previously prepatent infections. The eff-
communication).
cacy of praziquantel is lower against immature stages of
At present, reinfection after treatment is almost inevit-
S. japonicum in hamsters (WEBBE & JAMES, 1977) and
able in ,tibodiene because no alternative water supply
those of S. mansoni in mice (SABAH et al., 1986). Adults
exists. Treatment and health education, water manage-
were signifïcantly less commonly infected 12 weeks after
ment and weed control of the small irrigation canal are
treatment than children. This could be explained by the
the onlv immediatelv available tools for control. These
hypothesis that praziquantel works better in a mature
Will nott~liminate snail hosts of S. haematobium but could
immune system or by there being a lower rate of reinfec-
be sufficrent to control Biomphalaria pfeifferi. Obviously
tion due to either different exposure patterns or im-
the whole delta is at risk of schistosomiasis; the dynamics
munity to reinfection in adults.
of snail populations Will eventually determine the dis-
Since 1989 the villagers have been informed about the
tribution. of the 2 endemic species. The increase and eco-
cause of the haematuria, and nurses responsible for
logical changes of the water bodies may also influence
medical tare in the area were advised to consider haema-
other vector borne diseases, such as malaria.
turia a suffcient indication for treatment with praziquan-
The exact time of the introduction of urinary schisto-
tel. Since 1991, this drug has been available in the health
somiasis in Mbodiene is not known but it appears to have
posts at about US $3 for one adult treatment. Neverthe-
taken place at about the same time as the outbreak of S.
less, although only one-eighth of the price in private
mansoni in Richard-TO11 (TALLA et al., 1990). The paral-
pharmacies, this high cost may have limited the number
le1 explosive evolution of 2 different forms of schistoso-
of treatments. Only 8 treatments (7 children) were given
miasis in the same region is striking. Transmission in
in the fïrst 6 months of 1992.
both foci appears to be similarly intense in non-immune
In 1989, shortly after this new schistosomiasis focus
populations of the same ethnie groups. Epidemiological
had been identifïed, a preliminary survey was carried out
and immunological studies in both locations are under
on some 150 primary schoolchildren from the villages of
way and these new, neighbouring foci provide a unique
Ndioungue, Ndiaye, Diagambal and Guomene, sur-
opportunity to study schistosomiasis in general.
rounding Mbodiene (unpublished data). This survey did
not indicate any other new foci of S. haematobium, al-
Acknowledgement
though the situation in those villages was quite similar to
We grarefully acknowledge the work of Ngary Sy, Abdoulaye
that in Mbodiene. There are now indications that urinary
Yague. Sohibou Guindo, Sevdou Tine and Mankeur Dion (the
schistosomiasis has spread to those villages as well: in-
technicians). Special thanks go to WARUA (ADRAO), Senegal,
creasing numbers of cases of haematuria have been re-
which provided excellent working conditions on the spot, and to
ported in routine health statistics from the area. In Mak-
ORS.rOLti fOr logistic SLIppOrt.
hana and Mbarigot, prevalences of up to 87% were found
This work was supported by the Flemish Community of Bel-
in children 5 to 14 years old
eium and bv the Science and Technoloev for Develoument oro-
(KONG~, 1993). S. haemato-
gramme of fhe Commission of the Euroyean Commuiities, ion-
bium had never been reported in these villages before;
tracts no. T52-0145NL and T53-CT91-0041 (University of
however they are located in the immediate surroundings
Leiden) and T52M-0079-F and T53CT91=0030
(Institut Pas-
of the village of Lampsar and are probably part of this
teur, Lille) and is associated with the ESPOIR programme for re-
old focus.
search ancl control of schistosomiasis in northern Senegal.
The available data suggest that Bulinus globosus i s a
main intermediate host in Mbodiene and, given the high
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October 1993
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406
Schistosomiasis in the Republic of Sao Tomé and Principe: human studies
J. Almeda’, M. Corachanl, A. Sousa2, C. Ascaso3, J. M. Carvalho2, D. Rollinson4 and V. R. Southgate”
*Secci&z
de Medicina Tropical, Hospital Cl&ic, Barcelona, Spain; 2Ministerio da Saude, Republica De Süo Tomé e Principe;
3Departamento de Bioestadistica, Universidad de Barcelona, Spain; 4Department of Zoologv, The IVatural Histoy Museum,
Cromwell Road, London, S W7 SBD, UK
Abstract
The only schistosome species found in stool specimens in the local population of the republic of Sao Tomé is
Schistosoma intercalatum. An initial survey of schoolchildren showed an overall prevalence of 10.9%, with
some schools reaching 29%. No S. haematobium egg was found in 782 urine specimens from the local popu-
lation, although some were seen in the urine of Angolan soldiers stationed near the capital City. One village
in the endemic area, San Marçal, had an S. intercalatum prevalence of 43%, with 14 persons >40 years of age
harbouring severe infections. The transmission area is restricted to the north-east of the main island, where
5 foci apparently account for most of the infections. Seven cases recorded from Principe may be explained
by the fact that the children were attending school at Sao Tomé. Women carrying out domestic activities are
more at risk of contracting the infection because of longer periods of water contact than men. The morbidity
produced by the infection is restricted to splcnomegaly and blood in the stools. High prevalences have been
found of Ascaris lumbricoides and Trichuris trichiura, and hookworm and Strongyloidesstercoralis
were also ob-
served. Praziquantel was well tolerated and appears to be a good tool for control purposes, although reinfec-
tion in the transmission area apparently occurs rapidly. Control strategies based on chemotherapy should
take into account an older age group as well as the schoolchildren. Focal mollusciciding and the introduction
of washing facilities may also have a role to play in control. The possible recent introduction of the infection
to the island is discussed.
Introduction
Materials and Methods
Sao Tomé and Principe are 2 islands in the Gulf of
A survey was conducted in 1991 of 2930 schoolchild-
Guinea, approximately 245 and 2 17 km from the main-
ren (aged 5-15 years) from 26 schools in Sao Tomé for
land, with populations of 114 507 and 5637, respec-
intestinal helminths and faecal and urinary schistoso-
tively.
miasis. In addition, 100 pupils from the 2 main schools
The Atlas of the Global Distribution of Schistosomiasis
of the island of Princine Paeué district1 were examined
(DOUMENGE et al., 1987) states that about 30% of the
by the Kato-Katz techiiqbe ~KATZ et al:, 1970); 3 slides
children in Sao Tomé were infected with Schistosoma hae-
were prepared from each stool sample. Seven hundred
matobium, but GRACIO (1988) found snails of the Bulinus
and eighty-two urine samples were examined by filtration
forskalii group and suggested that schistosomiasis could
as described by PETER~ (1976); they were checked for
be caused by S. haematobium, S. intercalatum and a hy-
gross haematuria and examined for haematuria and pro-
brid. However, a detailed survey of 1637 island children
teinuria with chemical reagent strips (Hemastix@ and Al-
(ROMERO et al., 1989) showed the presence of schisto-
bustix@) , ,AMES laboratories). Urine samples from 332
some eggs in stool samples only; they were identified as
schoolchlldren infected with S. intercalatum were exam-
S. intercalatum. CORACHAN et al. (1988) described the
ined similarly in 1992.
fïrst clinical case S. intercalatum infection in an immi-
An earlier indication of an S. intercalatum prevalence
grant from Sao Tomé.
of 11% (ROMERO et al., 1989) led us to choose a sample
In order to clarify the situation, a programme was de-
size of 3030 pupils from a total of 20 000 schoolchildren,
signed to provide information on the epidemiology and
based on the local census. Cluster sampling was used,
biology of schistosomiasis and to assess prospects for its
first stratifying by districts and then by schools, propor-
future control in Sao Tomé. The present paper refers pri-
tionally to the number of children per school.
marily to the clinical and epidemiological aspects of the
A questionnaire relating to morbidity, water contact
study.
patterns and persona1 data was administered by 2 phys-
Human infections with S. intercalatum were described
icians and 2 fïeld workers. Al1 questions concernmg
comprehensively by FISHER (1934) in Zaire. S. intercala-
symptoms related to their presence in the last month.
tum -is present -in- 5 countries, according to a World
The physicians physically examined a11 children. The
Health Oreanization survev JIAROTSKI
& DAVIS.
questionnaire had been previouslv validated by repeated
1981 jChas? Central Afric& Ripublic, Gabon, Came:
testing with local personnel. Al1 infected persons found
roon and Zalre-and subsequently reports reflecting a
during the fïrst survey (1991) were treated and re-exam-
wider distribution have appeared. Clinical infections in
ined at intervals of 3 and 12 months. In every survey, in-
immigrants from Equatorial Guinea were descrihed by
fected persons were treated with 40 mg/kg praziquantel
MAS et al. (1985) and CORACHAN et al. (1987a), and a
in a single dose. Mebendazole (100 mg/12 h for 3 d) was
survey in that country revealed a focus of the infection in
given totreat other intestinal helminthi. A new stooi sur-
a district of Bata, the capital city (SIMARRO et al., 1989).
vey of 2856 children, which did not include the cases
Infections in Spanish tourists from Mali were described
found in 1991, was conducted in 1992.
from a travellers’ clinic (CORACHAN et al., 1987b, 1992).
A survey for S. intercalatum was made in 1991-1992 of
The infection has also been reported from Nigeria
a11 752 inhabitants (470 females and 282 males) of the vil-
(ARENE et al., 1989).
lage of San Marçai in Sao Tomé. Urine saiples from
The objectives of the study in humans were to deter-
these 752 persons were also examined by filtration.
mine the prevalence of schistosomiasis in children of
In addition, a small sample of Angolan soldiers based
school age, to assess the morbidity and therapeutic re-
at the airport were examined for schistosomiasis infec-
sponse of the infection, to establish the pattern of water
tion.
contact in the endemic areas, and to monitor the dis-
tribution of infection in the whole population of a village
Results
in an endemic area.
Parasitology
Address for correspondence: Dr J. Almeda, Seccibn de Me-
School survey. The only Schistosoma species found was
dicina Tropical, Hospital Clinic, Villarroel 170, 08036, Bar-
S. intercalatum; 332 children (10.9%) in the first survev,
celons, Spain.
and 333 (11.7%) in the second were infected, comprisi&