O efeito da infecção por Schistosoma mansoni na morbidade infantil no Estado da Bahia, Brasil: I — Análise do nível ecológico.

Rev, Inst. Med. trop. São Paulo 26(4):230-235, julho-agosto, 1984

THE EFFECT OF SCHISTOSOMA MANSONI INFECTION ON CHITD MORBIDITY

IN ThIE STATE OF BAHIA, BRAZIL

I

_-

ANATYSIS AT THE EGOLOGICAL LEVEL (*)

Mauriclo L. BA.RRETO and Sebastlão LOUREIRO

SUMMARY

This investigation ,was carried out

in

10 small towns

of

the State

of

Bahia (Northeastern

_Brazil).

The objective 'was

to

study

the

correlations between the prevalences

of

liver

and spleen enlargment

in

different areas and the pre-valence and intensity

of

Schistosoma mansoni infection

in

the same areas. Our conclusions are

that:

a)

schistosomiasis mansoni morbidity (prevalences

_of

he-patomegaly and splenomegaly) was directly correlated

to

the

prevalence and

intensity

of

infection;

b)

the intensity

of

infection

of a

community

is

a

good indicator

of

morbidity and explain the morþidity variation between areas better

than

the

prevalence

of

infection;

c)

the

prevalence

of

splenomegaly and the mean size

of

the liver

in

the mid-sternal line appear

to

be good indicators of the S. mansoni prevalence and intensity

of

infection

in a

community. Our con-clusions raised the possibility

of

construction

of

definitive regressions equations between indicators

of

morbidity and indicators

of

infection, so

that

the value

of one could be used to predict the other.

UDC 616.995.122

INTRODUCTION

A strong relationship between intensity of

infection with Schistosoma mansoni and

mor-bidity has been demonstrated

in

several

popu-lations.

This phenomenon

is

clearest

in

chil-dren

in

hiperendemic areas 7,4,5,12,L4,2a,21. _ll1lg

led to the hypothesis that morbidity ,would vary between areas with differents prevalences and

intensities

of

infection.

This hypothesis has been accepted,

but not

studied ,with adequate methodologY e'to.

This investigation was designed

to

study

this

question

in

_{more detail.}

_It

focuses on hepatomegaly and splenomegafy, the most

im-portant signs

of

morbidity from schistosomia-sis mansoni infection s.

POPULATION AND METHODS

This stu{y was carried out

in

the State of Bahia, in the Northeastern Region of Brazil. This State has a.n area of 559.921 square kilometers

and a population

of

around 10 million inhabi-tants¡. The incidence of malaria has been low

in

the State

in

the recent years, and most of

the cases were either im'oorted

or in

isolated focus.

The State has been divided into 26 Homo-genous Microregions (MRH)

_þy

the

National

Institute of Geograptry and Statistics (FIBGE). .Each of these MRH include several municipali-ties.

Previous surveys demonstrated

that

there was a large variation in the prevalence of S. man-soni infection in this State, from hyperendemrc (*) _This Department of Preventive Medicine, Federal. university of Bahia. VaIe d.o canela, 40.000 Salvador-8a.. B&ASIL

BAR'R'ETO, M' L, & LOUR'EIRO, S. - The effect of Schistosome ma.nsoni infection on child morbidity in the State of

Bahia, _{Brazil' I -} Analysis at the ecological level. Rev. Inst. Med. trop, São paulo 26:280-285, 19g4.

to

parasite-free areasT'le; an ideal situation to testing the Ïgryothesis.

Children between 5 and 16 years old were studied

in

ten differents small towns

of

the

State

(Fig.

1). A

four-stage random sample scheme

was employed.

In

the first

stage 10 MRH were selected;

in

the second one

mu-nicipality in each MRH;

in

the third one town,

with a population of 500 to 2000 inhabitants, in

each municipality; and at the fourth stage, after

a census, 25% ot the population bet\Meen b and 16 years old were selected. This resulted

in

a

sample

of

978 children with complete data on 840 ß63Vo).

Jaguarari O

I botirama

o

Lencois O

Stool Examinaltion

Each children was provided ,with one pre-viousþ identified cup

for

colection of a faecal sample. From each sample two thick smears were prepared, using the Kato technique as

modified

by

KATZ

et

al.

li.

A

commercialþ-available

kit

v¡as used (Boehringer Mannheim

Bioquimica S.4., Rio de Janeiro, Brazil).

Physical Examination

Individuals were examined

for liver

and spleen enlargment

in

the supine

position,

If

O _{Ruy '}

Baroosa ^ !

LOnOe

0 I00

200 Km t--- ---{

SCALE

Fig. 1 _- Map of the Stâte of Bahia showing the location of 10 sample towns Itacare

the

liver

r¡¡as palpated, the distance between the liver edge and the right costal margin was measured

in

the midclavicular line (MCL) and from the xiphoid in the midsternal line (MSt).

If

the spleen was palpated, the distance from the left costal margin to the spleen edge was measured

in

the anterior axilary line. The

exa-mination were performed without knowledge

of

the stool

results.

Hepatomegaly was defi-ned as being present when the liver was

BARR'ETO, M' L' & LOUREIR'O, _{s. -} The effect of Schistosoma mansoni infection on chitd morbidity in the State of

Bahia, _{Brazil. I -} Analysis at the ecological level. Rev. Inst. Med. úrop, Sio paulo _{26:290.235, 19g4.}

being present whenever the spleen ,was palpa-ble.

Variables

For each town were calculated: a) the pre_ valence

of

S. mansoni infection

(Xr);

_b)

_the

intensity

of

infection

_in

all

children examined

(Xr) (the _{geometric mean of eggs per gram of} stool

_{in all}

children examined was calculated, meanwhile 1.0 was added to each egg count to

avoid values zero

_in

the

calculation

_of

loga_

rithms);

c)

the

prevalence

of

_hepatomegaly

(Y,);

_d)

the prevalence

of

splenomegaly (yr);

e)

the mean size

of

the liver below the right costal margin

in

the wISL

(\); f)

the mean size of the liver below the xiphoid

in

the MCL (Yo).

Regression equations were computed,with X, and

X,

as the independent and

yr, yr,

y,

and Yo as the dependent variables. Correlation

coe-ficients

(r)

_{and determination coeficients} (r2)

were also computed. The

p

values were com-puted using a one-sided

t

test tz.

RESULTS

The number

of

children examined.

in

each town and the value

of

the

several variables are presented

in

Table

I.

The prevalence of

S. m.ansoni ranged from 0

to

BI.7%, while the intensity of infection ranged from 0 to 5b eggs

per gram of

stool.

Similarly, all the other

va-riables varied considerably between areas.

Figures 2 and 3 present a summaly of the

analysis. The intensity

of

infection (Xr) was significantlSr associated rwith

_all

the depend.ent

variaþles. The correlation between

X,

(preva-lence of S. mansoni infection) and the outcome variables were stafistically significant for yr,

y,

and Yo,

but not

quite statistically significant

for

Y,

(r-0.543, p:0.052), although

it

'was in the expected direction and

of

reasonable mag-nitude.

For

every outcome varÍable,

the

associa-tion

with

the intensity

of

infection was

stron-ger than

for

prevalence. The prevalence of splenornegaly

(%)

ano

the

mean size

of

the liver in the MSL (Yr) gave the highest correla-tion coefficients as well as determination coeffi-cients 'with both independent variables.

The intensily of infection (X2)

in

the town

of Conde was r¡uch higher than

in

any other

(Table

I,

Fig.

2).

If

this town's results was excluded from the analysis only the correlation

of Y,

with

X,

remain statisticalþ significant

(Y2

_-

_7.73

₊

_{0.25 X2,}

_{r :}

_0.781,

_rz

_:

_0.610,

t -

3.54, Þ

:

0.005), however the other varia-bles' correlations remained

in

the same

direc-tion

and

of

reasonable magnitude

(r =

0.4?1,

0.532, 0.386 respectivelly for

y,,

_\

and yo). DISCUSSION

Schistosoma mansoni

is

an important cau-se of morbidily

in

infected population and be-cause of this the need

for

its control has been

Municipality Ibotiruma

Itacare

Barra do Choca

Rui Barbosâ

Cruz das Almas

Mutuipe Jaguarari Jorro

Conde Lencois

TABLEI

values of the basic variables in each of the 10 studied towns of the state of Bahia, Brazil

No. Examined Xl _E yr

X1 _- P¡evalence of S. mansoni infection (o/o)

X" _- Intensity of S, mansoni infection (Geom. mean of eggs/g of stool)

Y1 _- Prevalence of hepatomegaly (o/o)

Y" _- Prevalence _of splenomegaly (%)

Y.r

-Mean size of the liver in MSL (cm.) Y{ _- Mean size of the liver in MCL (cm.)

96

82

't5 94 88 87 62 92

81

0.0

10.5

ó1. o 41.8 49.0 60.0 71.4 't7.9 81.7

0.0

r.2

4.4 10.8 34.4 26.1

25.0

21.0 2.5 t.11 0.86

23.7 0.0 1.06 0.?8

12.3 1.3 0.59 0.63

zL.L 5.3 1.5? 0.93

34.2 5.1 2.06 0.54

10.6 2.2 0.86 0.45

30.6 11.8 1.?8 0.51

48.5 7t.4 z.zg 1.55

55.2 13.S A.B? 1.99

21.5 3.3 1.46 1.63

BARR'ETo, M. L. & LOUREIR'O, s' - Tt¡e effect of Schisúosoma mansoni infection on child morbidity in the state of

Bahia, Brazil. _{r -} Analysis at the ecological level. Rev. Insú. Meil. trop. São p¿ulo 26'.280-2g5, IgB4.

Y1 _- Prevalence of,

hepatomegaly (9í)

., _¡l 60 50

X1 _- Prevalence of infection (îó)

40 JO 20 IO

Y2

Y2 - Prevalence of splenomegaly (9ó)

20 40 60 80 X1

Y1 : 17.0 + 0.25 X1

r ₌ 0.543 _{12 =} O.2J5 t=1.81 p _=0.052

X2 - Intensity of inf,ection (Geometric mean of eggs/g. of sloo.I )

l6 t4

T2 IO

I

6 4 2

Y2 _{= 0.89} + 0.11 X1 Yz ₌ I_99 + O.22X2 t ₌ 0.699 rZ ₌ 0.489 r ₌ 0.851 rZ _{= O.tZl}

t =2.17 p =0.012 t =4.62 p =0.001

Fig' 2 _- Prevalenæ (Xr) and intensity (xr) of infection by S, mansoni corrêtated with the pre.

valence of hepatomegaly (Yr) and prevalence of hepatomegaly (1¿") in 10 tovms. Bahia, Brazil

stressed

æ.

However

the

implementation of effective control measures has p,roved difficult, especiaUy

in

large developing coì.rntries such as Brazil 18.

Brazil has large regional and local varia-tions

in

infection rates 7,1e. The reasons for these variations

are

in

general retated \¡/ith characteristics of the focus 1 _{and the frequency}

of

the

human contact ,with

the

fssusl,ó,8,16. However, the most important factor

_-

at least in Byazil

_-

seems to be the directions of popu-lations movements

in

the country's history z,ts.

In

the present study we have documented

that:

a)

schistosomiasis mansoni morbidity (prevalences of hepatomegaly and

splenomega-iy)

in children in different areas of Bahia, Bra:

zil,

was directly correlated

to

the prevalence and intensity of infection with the S. mansoni;

b) the intensity of infection is a good indicator of morbidity and explains the variation in

mor-Þidity better than the prevalence

of

infection;

c)

the

prevalence

of

splenomegaly and the

l0 20 l0 40 5o 6o x2

Yl=tS.O+0.54X2 ¡ = 0.706 12 = 0.498 t =2.8? p =0.011

20 40 60 80 X1 l0 20 30 40 50 60 Xz

mean size of the liver in the MSL appear to be

good indicators

of

the S. mansoni prevalence and intensity of infection

in

a community.

Our

conclusions raised the possibility of construction

of

definitive regression equations between indicators of morbidity and indicators

of infection, so that the values of one could be used

to

predict the

other.

The fact that we study ontry few areas was possible responsible

for

some

of

the irregularites

in

our

analysis, such as the problem of the value of the

inten-siff

of

infection

in

the town

of

Conde. How-ever, the constant high values of the correlation

and

determination coefficients

were

stongly sugestive that the occasional aþsence

of

statis-tically

signifficant correlations, were due the small number

of

areas studied.

Since KLOTZEL 12 _observed the relationship

BAR'R'ETO, M. L. & LOUREIRO, _{S. -} The effect of Schistosoma mansoni infection on child morbidity in the State of

Bahia, _{Brazil. I -} Analysis at the ecological level. Rev. Insú. Med, úÌop. São Paulo 26:230-235, 1984.

Y3 J Y3. - l'4ean size of the liver in lilsL (cm) 2

I

Yr - P¡owalanno nF

infection (9ó)

Y4

Y4 - Mean size of the liver in MCL (cm)

20 40 60 B0 X1

Y¡ ₌ O.eZ + 0.02 Xt r ₌ 0.658 r? _{= 0.411} L =2.47 p :0.01,9

X2 _- Intensity ol infectron (Geomctric mean of e99s/g. of stool )

Y4 _{= 0.52} + 0.01 X1 _{y4 = 0.66} + O.O2X2 ¡ ₌ 0.610 rZ ₌ O.)t? r ₌ 0.681 .J _{= 0.q64}

t =2.18 p =0.011 L =2.6J p =0.0t5

Fig. 3 _- Prevalence (x1) and intensity (x") _{of infection by S. mansoni correlated. with the mean}

size of the liver Ín MSL(yr) and in MCL(Y{) in 10 towns. Bahia, Brazil þy the selective treatment of persons with high

infection loadt3,22. However,

the

definition of

a communiüy level of prevalence and intensity

of infection represents more than the dinamics

of infection in the community, because, as was demonstrated

_{here and}

elsewhs¡s4,e,10, they also reflect the general level of morbidity. This enables one to think about of the prevention of

the schistosomiasis morbidity and stresses the importance of measures to decrease, in perma-nent basis, the prevalence and infection rwhen

control

of

transmission

_is

not

possible. The Iesults reported here suggest

that

actions di-Iected to,wards

a

reduction

in

the prevalence and especiaUy

in

the intensity of infection will be benefical

in

diminishing

morbidiff

in

the population.

RESUMO

O efeito da infecção por Schistosoma mansoni

na

molbidade

infantil

no

Estado

da

Bahia. Brasil.

I -

Análise do nível ecológico

IO 20 iO 40 50 60 x2

: Ì.05 + 0.04 X2

: 0.798 r2 ₌ 0.6J6 =3.75 p =0.003

v3

r t

20 40 60 80 X.t l0 20 30 40 50 60 x.¿

Esta investigaçáo

foi

levada

a

efeito em 10 pequenas cidades do Estado da Bahia (Nor-deste do Brasil), escolhidas através de um pro-cesso amostral. O objetivo foi estudar as cor-relações entre as prevalências de

hepatomega-lia

e esplenomegalia, em diJerentes áreas, com a prevalência

_{e a}

intensiclade

da

infecção pelo S. mansoni nas mesmas áreas. Nossas conclu-sões são:

a)

a

morbidade esquistossomótica

(prevalências _{de hepatomegalia e}

esplenomega-lia) foi

diretamente correlacionada com a pre-valência e a intensidade da infecção;

b)

a

in-tensidade

da

infecção (medida pelo número de ovos nas fezes) mostrou ser um bom in-dicador do grau de morbidade, explicando a

và-riação

da

morbidade entre

as

áreas melhor

que

a

prevalência da infecção;

c)

a prevalêÐ-cia de esplenomegalia

e o

tamanho médio do

BARRETO, M' L. & LOUR'EIR'O, S. - The effect of Schistosoma mansoni infection on child. morbiditJ¡ in the Stâte of

Bahia, _{Brazil. I -} Analysis at the ecological level. Rev, Inst. Med. úrop. São Paulo 26:230.285, 1984.

a possibilidade da construção de equações de regressão definitivas entre indicadores de mor-bidade e indicadores de infecção, de

tal

forma

que o valor de um possa ser usado pârâ predi-zer o valor do outro.

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