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Annals
of
Tropical Medicine and
Parasitology,
Vol. 91,
No.
4,
379-391 (1997)
Country-wide rapid epidemiological mapping
of
onchocerciasis
(REMO)
in
Cameroon
BY
J,
M.
MACÉ
GEOS,
U&wrsité Paul Valéry Montpellier III,
3.
P.
5043, 34032 Montpellier
Cedex,
France
iCP%
M.
BOUSSINESQ
-
ORSTOM,
CS
5,
213
rue
La
Fayette, 75480 Paris
Cedex
IO,
Frame
P.
NGOUMOU
Ministry
of
Public Health,
P.
O.
Box
12892, Yaounde, Canieroon
J.
ENYEGUE
OYE
Sight
Savers
International,
Cameroon
Ofice, Coalition
of
NGDOs,
P.
O.
Box
4794,
Yaouizde,
Ca.meroon
A.
KOÉRANGA
Délégation Provinciale
de
la
Santé Publique,
Garoua,
Canieroon
AND
c.
GODIN"
Organimtion
pour
la
Préuetztion de la Cécité,
9
rue
Matlzurin Régnier, 75015 Paris,
Fran
Received 22
Januarj~
1997, Accepted 4
Februaty
1997
The prevalence of infection in local communities has been used
as
the basis for the country-wide
repartition of onchocerciasis in Cameroon, following the principles for rapid epidemiological mapping
of
onchocerciasis
(REMO)
developed by the World Health Organization. The levels of endemicity were
evaluated in
349
villages by rapid epidemiological assessment
(REA),
a
method based
on
the examination
of nodules in males aged
2
20
years.
An
onchocerciasis map
was
then drawn from the epidemiological data
which had been collected previously, from clinico-parasitological surveys based on the examination of
skin
snips, and the results
of
the
REA
surveys. The
REMO
surveys allowed the main onchocerciasis foci
in
Cameroon to be accurately delineated, and several small endemic areas which had never been reported
before to be identified. The total 'at risk' population (i.e. those for which ivermectin treatment should be
considered
as
urgent or highly desirable) .was estimated by combining the epidemiological results and the
demographical data available from an administrative census. Those at risk were estimated to number
3.5
million, representing about
50%
of the total rural population in Cameroon.
Ivermectin (Mectizan@) has proved to be a
very
effective and safe drug for large-scale
treatment
of
onchocerciasis. In
1987,
the man-
ufacturers, Merck and
Co.
Inc., decided to
donate the drug, free of charge and for as long
as needed, to any government or non-govern-
mental development organization
(NGDO)
in-
*
Author
tÓ
whom correspondence should be addressed.
Fax:
+33 14061 0199.
0003-4983/97/040379-13
$9.00
Carfax
Publishing
Ltd
volved in onchocerciasis control,
As
a result of
this decision, country-wide ivermectin distri-
bution programmes
(IDP)
are being developed
in
most
of the countries where the disease is
endemic, in the hope that onchocercal blind-
ness and severe skin disease can be prevented
in the near future. Most
of
those countries
which, though at-risk, are outside of the area
of the Onchocerciasis Control Programme in
West Africa
(OCP),
are now covered by the
O
1997 Liverpool School
of
Tropical Medicine
380
MACÉ
ET
AL.
African Programme for Onchocerciasis Con-
trol (APOC). In the APOC area, no large-scale
vector-control operations can presently be en-
visaged and control of onchocerciasis depends
almost entirely on ivermectin. Although Mec-
tizan@ is available at
no
cost, governments and
NGDO planning
IDP
still have to pay for the
drug's distribution. There is general agree-
ment that the drug should be distributed first
to those communities whose members are at
risk of developing the severe and disabling
ocular or dermal complications of onchocer-
ciasis (Taylor
et
al.,
1992). In general, this risk
is directly related to the intensity of infection
in the community (Remme
et
al.,
1989). There
are several reviews which present data on the
distribution of onchocerciasis outside
of
the
OCP area and give information on the most
severely affected regions (Crosskey, 1981;
Boussinesq, 1991a; Fain, 1991). However, the
epidemiology of onchocerciasis remains un-
known in many areas, one of which is
Cameroon, and surveys have to be carried out
urgently to fill these gaps in our knowledge.
The classical parasitological method for as-
sessing the endemicity of onchocerciasis in a
region, based on the examination of skin snips,
cannot be used routinely because it is unpopu-
lar, time-consuming, costly, and may spread
hepatitis B virus and HIV. The World Health
Organization has therefore adopted and devel-
oped an alternative method, known as rapid
epidemiological assessment (REA), which is
based on the prevalence of nodules in males
aged 220 years and which was suggested by
Taylor
et
al.
(1992). Using this method to
assess community endemicity levels, and se-
lecting communities according to the princi-
ples described by Ngoumou
et
al.
(1994), it
has been possible to accomplish an initial
rapid epidemiological mapping of onchocer-
ciasis (REMO) over almost the whole of
Cameroon. Now that the main endemic areas
have been defined by REMO, further REA
within those general areas which are selected
for
IDP
will reveal exactly which communities
are above the threshold level of endemicity
that calls for mass treatment with ivermectin.
The aims of the present study were: (1)
to
produce a map of the general distribution of
onchocerciasis in Cameroon, by combining the
results of a considerable number of clinico-
parasitological surveys (CPS), carried
out
for
public health or research purposes before
1993, with the results of the REA surveys
during 1993-1995; and (2) to estimate the
total number of people exposed to severe
onchocerciasis in Cameroon by combining all
the epidemiological and demographic data
available.
SUBJECTS AND METHODS
At the time of launching the REMO epercise
in Cameroon, it was decided that no REA
surveys would need to be performed in five
areas because epidemiological data were al-
ready available for them from previous, large-
scale CPS. These areas were the wide belt
which extends across the Sudan-savanna area
in the North Province (Anderson
et
al.,
1974;
Le Bras
et
al.,
1976; Louboutin-Croc and
Madi Kambaba, 1983; Boussinesq, 19916;
M.
Boussinesq, unpubl. obs.), the limited focus in
the Extreme-North Province (Pabot du
Chatelard
et
al.,
1978; Stéveny
et
al.,
1981;
Marceau
et
al.,
1986), the region of forest-
savanna mosaic located in the Central Prov-
ince, at the confluence of the Sanaga and
Mbam Rivers (Ripert
et
al.,
1977;
M.
Boussi-
nesq, unpubl. obs.), the forested Mungo and
Meme Valleys in the South-West Province
(Duke
et
al.,
1972; Anderson
et
al.,
1974;
Moyou Somo
et
al.,
1993), and the forested
Dja Valley area in the South Province (Kollo,
1993;
J.
Gardon, unpubl.
obs.)
(Figs
1
and 2).
REA surveys were planned in the remaining
areas, the data for which were very scarce,
rough or completely absent. Despite the avail-
ability of clinico-parasitological data (Brengues
et
al.,
1975), REA surveys were performed in
the Noun Valley (West Province) because
more accurate information was considered
necessary to plan a rational IDP in this very
densely popdated area.
Clinico-parasitological Surveys (CPS)
The numbers of communities and patients
examined during the large-scale CPS carried
out bc
All, ei
were
and
s
Ifzstitn
le
De
19916
preva
stand,
et
al..
REA,
The
1995
tail p
the p
staue<
-?
majo]
(BGI
on
tl
river
(BG;
hydr
sites
consi
patte
with
most
ciasir
met1
logic
map
arca!
also
knoi
POP'
natic
fore
sout
area
blac
swa
lian
area
7
of
E
wit1
the
15
y'
(Ngc
MAPPING
OF
ONCHOCERCIASIS IN CAMEROON
381
out before 1993 are summarized in Table
1.
All, except those carried out in the Dia Valley,
\$rere based
on
examination of both nodules
and skin snips in people of both sexes aged
15
years. During the CPS carried out by the
Institut
Franfais
de Recherche Scient$qiie pour
le Developvielit en Coopération
(Boussinesq,
19916;
Nl.
Boussinesq, unpubl. obs.), the
prevalences of microfilariae were age- and sex-
standardized using the
OCP
method (Moreau
et
al.,
1978).
REA/REMO Surveys
The REMO survey carried
out
during 1993-
1995 followed the principles described in de-
tail previously (Ngouniou
et
al.,
1994). Briefly,
the process was developed in three successive
stages.
First
the country was divided into six
major
bioclimatic/biogeographic
divisions
(ßGD),
which were then further sub-divided,
on the basis of the watersheds of the major
river-drainage systems, into a total of 21 zones
(BGZ),
each showing more or less uniform
hydrology in relation to potential breeding
sites for the
Siniuliim
vectors. Each zone was
considered to be uniform with respect to the
pattern of onchocerciasis transmission and,
within it, a sample of communities considered
most likely to be highly endemic for onchocer-
ciasis was chosen for survey, using the REA
method of Taylor
et
al.
(1992). The detailed
logical process used for the zoning, and the
map obtained, have already been presented
(Ngoumou
et
al.,
1994). During this stage, the
areas to be excluded from REA survey were
also identified. These included:
(1)
the regions
known as ‘empty zones’, where the human
population density is
<
1
inhabitant/km2 (i.e.
national parks, game reserves, areas of dense
forest, and the large savanna area located
south
of
the Adamaoua Plateau); and (2) the
areas totally unsuitable for the breeding of
blackflies (e.g. the densely populated but
swampy area in the eastern part of the Sahe-
Iian Extreme-North Province, and the summit
area of Cameroon Mountain).
The second stage of the
REMO
consisted
of selecting the communities to be surveyed
within each BGZ. The main criteria used were
the distance between the communities and the
rivers, and the location of the communities in
first, second, or third line, according to
the criteria defined in West Africa (Rolland
and Balay, 1969). In addition, the selection
was performed
so
that the maximal distance
between one selected village and the next was
5
50
km. Using this method, a total of 322
villages was selected for REA.
The third stage consisted in carrying out
the
REA
surveys themselves. The
REA
team
had four members (i.e. supervisor, nurse,
driver, and interpreter). The co-ordinates of
the villages surveyed were recorded with an
accuracy of 1
km
using
a
global positioning
system (Pyxis@ IPS360, Sony). The REA was
based
on
the examination, in each selected
community, of a sample of 30 adult males,
aged
220
years, for the presence of nodules
(Taylor
et
al.,
1992). The sample was selected
randomly from those residents whose activity
was principally rural.
Additional
REA
Survey
in
the Northern
Part
of
the North Province
In 1992, the NGDO River Blindness
Foun-
dation, in co-operation with the Cameroon
Ministry of Public Health, launched a mass
IDP in the North Province of Cameroon.
Baseline data were available from the CPS
quoted above, but the northern limit of the
meso- and hyper-endemic area was not well
defined.
A
specific REA survey was therefore
carried out to determine this boundary. This
was an important issue because
it
was decided
that the hypo-endemic communities of the
focus should only receive clinic-based treat-
ment. Owing to the greater degree of accuracy
required, the selection of the villages to be
surveyed was not done using the REMO pro-
cedure described above. Rather, it was per-
formed
so
that the maximal distance between
one selected village and the next was at the
most
5
km,
and
it
included
68
villages. Other-
wise, the examination was carried out follow-
ing the protocol described above.
Indices
used
for
Assessing Endemicity
Levels
As the cornerstone of the present study was
the REA survey, the main index used for
TABLE 1
The numberr
of
comnw~ities surveyed (AJCS) and subjects examined (NSE) and the epidemiological iadices recorded durifzg the cliuico-parasitological surveys
of
omhocerciasis in Cameroon prior to 1993
Surney area
NCS NSE
Index” Reference
Mandara Mountains, Extreme-North Province 7
1039 PN, PMF StCveny et al. (1981)
7 1000 PN, PMF Marceau
et
al. (1986)
Koza, Extreme-North Province 17
2657 CPI Pabot du Chatelard et nl. (1978)
Vina-IMbere Basin, North Province
6
1126
PN, CPI Anderson
et al. (1974)
13 lSO1 PN, PMF Le Bras
et al.
(1976)
39 11416 CPI Louboutin-Croc and Madi Kambaba (1983)
49 8828 PN, PMF Boussinesq (1991b)
Benoue Valley, North Province 5 795 PN, CPI Anderson
et al. (1974)
8
2124
CPI Louboutin-Croc and Madi Kambaba (1983)
7 1489 PN, PMF Boussinesq
(199111)
Faro-Deo Basin, North Province 48 6980 PN, PMF Louboutin-Croc and Madi Kambaba (1983)
14 1643 PN, PMF M. Boussinesq (unpubl. obs.)
Sanaga Valley (left bank), Central Province
5 1132 PN, PMF Ripert el
al. (1977)
25 4678 PN, PMF M. Boussinesq (unpubl. obs.)
Sanaga Valley (right bank), Central Province 39 7283 PN, PMF
M. Boussinesq (unpubl. obs.)
Noun Valley, West Province 12
1039 PN, PMF Brengues et al. (1975)
Mungo and Meme Valleys, South-West Province 4 702 PN, PMF Duke
et a/.
(1972)
11 1913 PN, CPI
Anderson
et al.
(1974)
4 1213 PN, PMF Moyou Somo
et a/. (1993)
Dja Valley, South Province
12 1567 PMF J. Gardon, unpubl. obs.
32 84G.t PN, PMF
Kollo (1993)
“‘PN, Prevalence of nodules; PMF, prevalence of skin microfilariae; CPI, clinico-parasitological index (percentage of patients with nodules and/or skin
microfilariae).
t All males aged 20 years.
MAPPING
OF
ONCHOCERCIASIS IN CAMEROON
383
\P
,
-----
25:
Swampy
areas
Il
-----
I
\\
I
384
MACÉ
ETAL.
Fig.
2.
The main towns and
rivers
of
Cameroon,
the
rural
population densities
in
each
administrative division
(dépnrtemcrzt)
and the boundaries
of
the provinces
-
--
and
dépnrtemenis
.. .
.
..
cc__
defining
tl
\vas
the
PI
aged
22C
defined thi
when the
desirable
Miere
class
non-enden
PNAM
(z
<
j0/o,
res
the target
be
reached
was
regari
resentative
As,
in
r
previous
cluded
>
value cou1
In the
fe
males had
results
ob
sidered
tc
endemicil:
25
gears
Aypo- ani
'
then distil
lence
of
4Oo/o-5
9
0,i
ively).
Tl
and meso-
posed pre
ivermectir
urgent
a
(WHO,
1'
Mapping
All the
REMO
pl
in the
No
using
a
ge
GIS@,
Sti
in which
were
plot1
the levels
lages,
thc
examined
those
n-11~
that
the
tinguishec
(WHO,
1s
MAPPING
OF
ONCHOCERCIASIS IN CAMEROON
385
defining the endemicity levels in the villages
was the prevalence of nodules in adult males
aged 220 years (PNAM). The WHO had
defined that ivermectin treatment was urgent
mhen the PNAM was
r40%,
and highly
desirable when the PNAM was 200/0-39%
(WHO,
1991). In the present study, villages
were classified as hyper-, meso-, hypo- or
non-endemic depending on the value for
PNAM
(
2
40%,
2Oo/o-399Ó, 5%-19%, and
<
5%,
respectively). In some small villages,
the target size
of
sample
(30
men) could not
be reached. In such places, a sample of 20 men
was regarded as giving a satisfactorily rep-
resentative picture of local endemicity.
As, in most of the villages surveyed in the
previous CPS, the population examined in-
cluded
>
20
adult males, a reasonable PNAM
value could be calculated from the CPS data.
In the few communities where <20 adult
males had been available, the parasitological
results obtained from skin snips were con-
sidered to give an accurate estimate of the
endemicity level when
>
100 residents aged
2
5
years had been examined. Hyper-, meso-,
hypo- and non-endemic communities were
thcn distinguished on the basis of the preva-
lence of skin microfilariae (PMF)
(
2
6O%,
40%-59%, 20%-39% and
<
20%, respect-
ively). The values corresponding to hyper-
and meso-endemicity correspond to those pro-
posed previously to define communities where
ivermectin treatment should be considered as
urgent and highly desirable, respectively
(WHO, 1991).
Mapping
All the villages examined as part of the
REMO project and the additional REA survey
in the North Province were plotted on
a
map,
using a geographical information system (Atlas
GIS’,
Strategic Mapping Inc.). The villages
in which >20 adult males were examined
were plotted in the form of pie charts showing
the levels of endemicity. Amongst these vil-
lages, those in which 20-29 persons were
examined were represented differently from
those where the sample size was higher,
so
that the less reliable values could be dis-
tinguished easily.
The few communities in
which <20 adult males were examined were
also plotted on the map, but the correspond-
ing estimates
o€
endemicity were not indi-
cated.
As those villages in the areas examined
during the CPS were usually relatively close
to one another, they were not plotted
on
a
map in the same way as the REA villages.
However, all the data available from the REA
surveys and
CPS
were combined in another
map, in which the hyper-, meso- and hypo-
endemic areas of each focus were delineated.
The limits of the administrative divisions,
which are the units used to estimate the num-
ber of people exposed to onchocerciasis (see
below), were included on this map.
Estimation
of
the Population Exposed to
Onchocerciasis
The population exposed to onchocerciasis was
estimated by combining the epidemiological
data obtained from the CPS and REA surveys
with the demographic data available from the
1987, country-wide, population census. The
geographical units used for estimating the ex-
posed population were administrative divi-
sions, for which demographic data were
available, and not the bio-geographic divisions
used for selecting the villages to be surveyed.
For various reasons, the demographic data
recorded at the lowest administrative levels
(i.e. the village and the ‘canton’) were not
available. The administrative unit used to esti-
mate the population exposed to onchocerciasis
therefore had to be at the higher level of
district
(‘nl.~oolzlzissemenl’).
At this level, the
1987
census distinguished urban and rural
populations.
As
the urban population was not
thought to
be
exposed to significant onchocer-
ciasis transmission, the estimates of the popu-
lation exposed to onchocerciasis were
calculated on the basis of the rural population.
The population in 1995 was estimated from
the
1987
figures by assuming an increase
of
2.9% per year.
No
attempt was made to delineate the hy-
per-, meso- or hypo-endemic areas within
a
given
nrroizdisseirrent.
As
the population within
an
awoizdissement
was often
not
homoge-
neously distributed, the proportions of the
386
MACÉ
ETAL.
~~
TABLE
2
Distribution
of
the
villages suivejied
$1
rapid epideiniological assessment
of
oncliocerciasis, according
to
the
iiuinbers
of
subjects/village
(da)
and
the
level
of
eizdeiiiicitji
No.
of
aillages
in
niain
survejr
No.
of
villages
iiz
survejl
iii
North
Province
Endemicity
2
30
s/v 20-29
s/v
3
20
s/v
I)
30
s/v 20-29 s/v
3
20
s/v
Non-endemic
50
13
63 17
O
17
Hypo-endemic
35
15
50
24
1
25
Meso-endemic
29
4
33 9
O
9
Hyper-endemic
126
15
141
9
2
11
All
240
47
287 59
3
62
population exposed to hyper-, meso- and
hypo-endemicity could not be estimated from
the proportions of communities found to be
hyper-, meso- or hypo-endemic in the CPS or
REA surveys. The level of endemicity was
thus considered homogeneous within an arron-
dissemeiit, and this level was defined by the
highest level recorded amongst all the villages
surveyed in the nrrondissemeat. Following
these principles, the ‘population exposed to
onchocerciasis’ or the ‘population at risk’ was
defined as the total rural population living in
the arrondissenimts where at least one meso- or
hyper-endemic village was detected by the
CPS
or REA surveys. Although geographical
and information constraints led to this
definition, it is probably a very useful
definition, in terms of any subsequent organi-
zation of ivermectin distribution, because the
arrondissements usually correspond geographi-
cally to health districts (‘districts
saizitaires’),
at
which level the health activities,
including
ivermectin distribution, are organized.
RESULTS
Results
of
the
REA
Surveys
A
total of 10 712 males aged
2
20 years, living
in 322 communities, was examined as part of
the main REAIREMO survey. The number
of men examined exceeded 30 in each of 240
of these villages, ranged between 20 and 29 in
another 47, and was
<
20 in the 35 remaining
communities. A total of 1831 males aged
2
20
years, living in 68 communities, was examined
as
part of the additional REA survey carried
out in the North Province; the number of men
examined exceeded 30 in 59 of the 68 com-
munities and ranged between
20
and 29 in
three others.
Combining the results from both REA sur-
veys, Fig.
1
shows the endemicity levels of the
349 communities in which at least 20 males
were examined, and Table 2 shows the distri-
bution of the surveyed villages according to
their level of endemicity.
Distribution
of
Onchocerciasis
in
Cameroon
Figure 3 combines the results of both REA
surveys with those of the CPS, and demon-
strates that five main hyperendemic foci exist
in Cameroon. Four of them have been de-
scribed by CPS: the two contiguous savanna
foci extending across northern Cameroon in
the Vina-Mbere and Benoue Basins; the Dia
and Lobo forest focus in southern Cameroon;
and the focus located along the Sanaga River
and the lower part of the Mbam River, before
its confluence with the Sanaga. The REA
surveys provided additional accurate details
on
the limits of these previously known foci, such
as the southern and northern limits of the two
contiguous foci extending across the North
Province. However, the main findings con-
cerned the western limits of the Sanaga-
Mbam focus, where the REA/REMO surveys
demonstrated that the hyperendemic areas ex-
tended westwards along the Noun River,
which is the main tributary of the Mbam
River, and that most of the West Province was
-
hyperenden
the REA
s
hyperender
%Vest Provi
demonstrat
tween this
focus. The!
because thc
are dense13
Other ir
in which i
the South
survey sho
known
Di
focus alon
was usual1
demic. Si
were founc
of Adamac
surveyed
I
Estimatic
Onchocer
Cameroon
administr:
year for
able), the
215
nrro?~
have beel
clinico-pa
endemic
1
SO
of
th
another
endemic,
was founc
dissemeizts
endemic
whole rui
to be 3 3:
people is
disseiizents
The pres
of count
onchocer
method,
(1992)
a
MAPPING
OF
ONCHOCERCIASIS
IN
CAMEROON
387
hyperendemic for onchocerciasis. In addition,
the
REA
surveys gave original data on the
hyperendemic areas located in the South-
West Province in the Cross River Basin, and
demonstrated that there is a continuity be-
tween this focus and the Sanaga-Mbam-Noun
focus. These results are particularly important
because the West and South-West Provinces
are densely populated.
Other interesting data concerned the areas
in which information was scarce, particularly
the South and East Provinces, where the
REA
survey showed that, apart from the previously
known
Dia
and Lobo focus and a limited
focus along the Ntem River, onchocerciasis
was usually non-endemic or only hypo-en-
demic. Similarly, the levels
of
endemicity
were found to be fairly low in the western part
of Adamaoua Province, which had never been
surveyed previously.
Estimation
of
the Population Exposed to
Onchocerciasis
Cameroon is divided into
10
provinces and
58
administrative
‘départememts’.
In 198’7 (i.e. the
year for which demographic data are avail-
able), the 58
départements
were divided into
21
5
arroiidissements.
In all, 108
arrondissements
have been surveyed, either by
REA
or by
clinico-parasitological methods, and hyper-
endemic communities have been recorded in
80 of them. Some of the communities in
another
11
arrondissements
were meso-
endemic, although no village in these areas
was found to be hyperendemic. Thus 91
arron-
dissements
were classed as meso- or hyper-
endemic and therefore ‘at risk’. In 1995, the
whole rural population ‘at risk’ was estimated
to
be 3 330
O00
people
(2
’795
O00
and 535
O00
people in hyper- and meso-endemic
arron-
dissements,
respectively).
DISCUSSION
The present results demonstrate the feasibility
of country-wide epidemiological mapping
of
onchocerciasis using the rapid assessment
method, which was proposed by Taylor
et
al.
(1992) and further developed by
WHO.
In
Cameroon, the
REA
surveys were carried out
by a team of four people who covered some
33 000 km during
175
days. The survey cost
about
U.S.$40
000,
or
US:$3.’73/person ex-
amined. This amount, which includes the
per
diems
of the team, the fuel and the mainte-
nance of one vehicle, might be considered as
reasonable, especially as
per
dìems
are relatively
high in Cameroon.
The only alteration which was made
to
the
REA/REMO
protocols of Taylor
et
al.
(1992)
and Ngoumou
et
al.
(1994) was in the mini-
mum sample size considered acceptable for an
accurate estimate of the level of endemicity.
Taylor
et al.
(1992) and Ngoumou
et
al.
(1994)
thought at least 30 adult males ought to be
examined to give a representative picture of
the community surveyed. Although attempts
were made to examine this number in each of
the present study communities, samples were
sometimes smaller. Rather than ignore all
of
the data for the smaller samples, endemicity
was estimated for communities where only
20-29 adult males could be examined. Figure
1
shows that the results obtained in these
villages, usually small ones, are generally simi-
lar
to
the levels of endemicity recorded in the
neighbouring communities where
>
30
per-
sons could be examined.
It
therefore appears
that a sample of 20-29 adult males is accept-
able and can give useful data
as
part of a
REMO.
At present, Cameroon and Nigeria are the
only two countries where a
REMO
has been
completed, (i.e. where most of the high-risk
communities have been located; Anon., 1996).
However, several areas have not yet been
surveyed in Cameroon because, although not
corresponding to ‘empty zones’, they were
sparsely populated (less than two inhabitants/
km2) and/or because the endemicity of
onchocerciasis in them is assumed to be low.
These areas were the swampy coastal area near
the boundary with Nigeria (BGZ Vb), the
coastal strip between the mouth
of
the Sanaga
and the boundary with Equatorial Guinea
(BGZ Va), the Upper-Sanaga (Djerem) and
Lom Valleys
(BGZ
IIIc), and the Kadei Valley
(BGZ IVb). The fairly densely populated
North-West Province (BGZ VIb), in which
388
MACÉ
ET
AL.
Hyperendemic
zones
8
Mesoendemic
zones
8
Hypoendemic
zones
Emptyzones
Fig.
3.
Distribution ofareas endemic for onchocerciasis in Cameroon. The boundaries
of
the provinces
(..
..
..)
and
départemenis
(white lines) are also shown.
-
the
\
Kimbl
proba1
also
r
Additi
formei
plete
1
Thc
been
survej
that
st
the
R
areas
than
c
nts
in
of blac
and
(.
sampll
males.
3
173
In
(
to
del
foci
a
on
se
the
d;
the
la
and
popul;
50
high
F
logical
savanr
the p
a
givc
popul;
lation
lence
the ir
a
Io\$
comm
logical
cate
tl
the
P
30
of
demic
had a
et
d,
The c
this ai
nts);
(:
MAPPING
OF
ONCHOCERCIASIS IN CAMEROON
389
the villages along the tributaries of the
Kimbe, Katsina Ala and Donga Rivers are
probably highly endemic (Duke, 1967), could
also not be surveyed for logistical reasons.
Additional
REA
surveys should thus be per-
formed in these felv areas in order to com-
plete the map of onchocerciasis in Cameroon.
Those areas of Cameroon that have not yet
been surveyed by any CPS or
REA/REMO
survey include:
(1)
the areas (just mentioned)
that still need to be surveyed
(53
arrondisseme-
fzts);
(2)
the areas excluded at the first stage of
the
RENI0
process (five
arrondissements
in
areas where the population density is
less
than one inhabitant/km2 and 27
arrondissenae-
rzts
in areas totally unsuitable for the breeding
of blackflies);
(3)
the 15 urban
arrondissements;
and
(4)
the seven
arrondissements
where the
samples in each village were all of <20 adult
males. Overall,
107
an.ondissements,
containing
3
173
O00
people, have never been surveyed.
In Cameroon, the REA surveys have served
to define the limits of previously reported
foci and have provided detailed information
on several hyperendemic areas for which
the data were fairly scarce. The largest of
the latter areas spreads through the West
and South-West Provinces, where the
population density is very high (exceeding
50
people/km2 in most areas). Such
high population densities may have epidemio-
logical consequences, In the West African
savanna, Prost
et
al.
(1979) found that
the prevalence of onchocercal blindness in
a
given community was partly related to
population density.
It
seems that high popu-
lation densities do not influence the preva-
lence of infection but lead to a ‘dilution’ of
the intensity of transmission, and thus to
a
low mean microfilarial density in the
communities. The results of a recent parasito-
logical survey
(J.
Kamgno, unpubl. obs.) indi-
cate that such
a
phenomenon may occur in
the West Province of Cameroon;
although
30 of the 41 villages surveyed were hyperen-
demic according to the PNAM, only five
had a community microfilarial load (Remme
et
al.,
1986) above
20
microfilariae/skin-snip.
The clinical consequences of onchocerciasis in
this area, which may thus be relatively mild
despite high levels of endemicity, should be
investigated further.
Besides the identification and delimitation
of the most severe onchocerciasis foci, the
results of REMO may be very helpful in
evaluating the populations at risk, for which
IDP are urgent or highly desirable, and in
planning the number of Mectizan@ tablets to
distribute every year in a given country. This
is all the more useful in the framework
of
the
launching of
APOC,
which aims
to
develop
self-sustaining, country-wide, community-
directed treatments with ivermectin in
16
en-
demic African countries outside the OCP
(Remme, 1995).
Ideally, the most elementary health
divisions should be used to estimate the pop-
ulations exposed to hyper-, meso- or hypo-
endemicity very accurately. In Cameroon,
these elementary divisions are the health areas
(‘aires de santeo),
each of which covers several
villages. Unfortunately, as no demographic
data exist for the health areas in Cameroon,
these divisions could not be used to estimate
the total population at risk. The calculation
had to be based on the higher level of health
district, each of which generally corresponds
geographically to an administrative
ayron-
dissemeizt.
Using this method, the population
at risk, as defined above, was estimated to be
about
3
330
000.
Adding estimates of the
‘at-risk’ populations in the few areas where
surveys are still needed to complete the map,
especially the North-West Province, the total
population
at
risk becomes roughly
3.5
mil-
lion, or about
50%
of the total rural
Cameroonian population. These values
confirm that onchocerciasis is an important
public-health problem in Cameroon. More-
over, although they represent the number of
people exposed to infection and not the popu-
lation actually infected, these values suggest
that the estimate of the number of infected
people in Cameroon (1.3 million), made be-
fore the launching of the REMO (WHO,
1995), was too low.
.
ACKNOWLEDGEMENTS.
The REA/REMO sur-
veys whose results are given in this paper
390 MACÉ
ET
AL.
were carried
out
with financial support from
the
River Blindness Foundation (RBF) and
the UNDP/World Bank/WHO Special Pro-
gramme for Research and Training in Trop-
ical Diseases (TDR).
The
CPS
carried out by
ORSTOM
received financial support from
TDR,
RBF,
and
ORSTOM.
This work would
have not been possible without the support
of
Dr
B.
O.
L.
Duke, who initiated
the
REMO
project in Cameroon and
who
was generous
with his advice and encouragement through-
out the study. We
are
also greatly indebted to
the Cameroon Minister
of
Public Health and
to
Dr
R.
Owona Essomba, Director of Com-
munity Health, for their help at the launching
of
the
REMO,
and
to
all
the
health authorities
for their assistance during the execution of the
surveys
in
the field.
We
wish to acknowledge
especially
Drs
Djibrilla and Abdoulaye in the
North Province.
We
are grateful to Drs
J.
Gardon,
J.
Kamgno and
B.
Kollo for having
kindly provided unpublished data, and to
B.
Bouchité, Dr
J.
P.
Chippaux,
A.
Demanga-
Ngangue,
T.
Nyiama and Dr
J.
Prod’hon for
their assistance.
We
also wish to thank the
technical staff of
the
RBF
in Garoua and the
Centre Pasteur in Yaounde.
27
REFERENCES
ANON.
(1996).
African Programne for Onchocerciasis Control (APOC). Report of the Second Session
of
the
Technical Consultative Comnzittee (TCC), Ouagadougou,
1-4
October
1996.
Mimeographed document.
Ouagadougou: African Programme for Onchocerciasis Control.
ANDERSON,
J.,
FUGLSANG,
H., HAMILTON,
P.
J.
S.
&
MARSHALL,
T.
F.
DE
C. (1974). Studies
on
onchocer-
ciasis in the United Cameroon Republic.
I.
Comparison
of
populations with and without
Oizcllocerca
volvulus. Transactions
of
the Royal Society
of
Tropical Mediciite and Hygiene,
68, 190-208.
BOUSSINESQ,
M.
(1991a). Répartition de l’onchocercose dans les états de 1’OCEAC: revue de la littérature.
Bulletin de Liaison et de Documentation de I’OCEAC,
98, 37-55.
BoUssImsQ,
M.
(199 lb).
Etude épidémiologique de l’onchocercose en zone de savane camerounaise. Effets d’un
traitement de masse par l’ivernzectine.
Ph.D. thesis, University of Montpellier
II,
France.
BRENGUES,
J.,
LE
BRAS,
J.,
FERRARA,
L.
&
OVAZZA,
L.
(1975). Enquête
sur
les filarioses en pays Bamiléké-
Bamoun, République Unie du Cameroun.
In
Proceedings
of
the
IOth
Co?$érence Teclzizique
de
I’OCEAC,
pp. 258-301. Yaounde: Organisation de Coordination pour
la
Lutte Contre les Endémies en Afrique
Centrale.
CROSSKEIY, R.
W.
(1981).
A
review of
Siinuliunz dainizosuirz
s.1. and human onchocerciasis in Nigeria, with
special reference to geographical distribution and the development of
a
Nigerian National Control
Ca-mpaign.
Tropenmedizin und Parasitologie,
32, 2-16.
DUKE, B.
O.
L.
(1967).
O~zclzocerca-Si~i~uliuiunl
complexes.
IV.
Transmission of
a
variant of the forest strain
of
Onchocerca volvulus. Annals
of
Tropical Medicine and Parasitology,
61, 326-33 1.
DU=,
B.
O.
L.,
MOORE,
P.
J.
&
ANDERSON,
J.
(1972). Studies
on
factors influencing the transmission of
onchocerciasis.
VIL
A comparison
of
the
Oitchocerca volvulus
transmission potentials of
Simirliuvz
dantnosum
populations in four Cameroon rain-forest villages and the pattern of onchocerciasis
associated therewith.
Annals of Tropical Medicine and Parasitology,
66, 219-234.
FAIN,
A: (1991).
Distribution and prevalence of onchocerciasis and its ocular complications in Zaire and Burundi.
Document WHO/ONCH0/91.166. Geneva: World Health Organization.
KOLLO;B. (1993).
Evaluation
of
alternate inethods
of
rapid assessment
of
Onchocerca volvulus
injëction in
liuman populations in a forested region
of
southern Cameroon: a
tool
for the classifcation
of
onchocerciasis
ende?nic comwunities
as
a step tomards control.
Ph.D. thesis, Tulane University, LA, U.S.A.
LE
BRAS,
J.,
BOUCHITE, B.,
LAMIZANA,
M.
&
BRENGUES,
J.
(1976). Enquête onchocercose dans le bassin
Vina-Pendé-Logone. Le foyer de Touboro. République Unie du Cameroun.
In
Proceediizgs
of
the
Ilth
Confirence Technique de I’OCEAC,
pp. 544-588. Yaounde: Organisation de Coordination pour
la
Lutte Contre les Endémies en Afrique Centrale.
LOUBOUTIN-CROC,
J.
P.
&
MADI KAMBABA,
T.
(1983). Résultat des différentes enquêtes épidémiologiques
onchocercose effectuées dans
la
Province du Nord-Cameroun dans le cadre du Projet inter-pays
d’étude de faisabilité d’une campagne anti-simulidienne
dans
le bassin de
la
Vina-Pendé-Logone.
Bulletin de Liaison
et
de Documeatation de I’OCEAC,
58,
33-5 1.
MARCEAU,
C. (19
(Mon1
MOEAU,
J
clinic(
MOYOU
Sc
MPOL
hyper
findin
NGOUMOU
distril
88,
+
PABOT
DU
Wanc
Orgai
PROST,
A.
Bulle
REMME,
J
Para!
REMME,
J.
its
ai
Vola
REMME,
J
infec
RIPERT,
C
l’onc
Pal11
ROLLAND
ON
(
gran
STEVEN\-.
Etuc
Cam
TAYLOR,
oncl
WORLD
I
WORLD
I
o11
(
sJ5t
I
MAPPING
OF
ONCHOCERCIASIS IN CAMEROON
391
MARCEAU, C., COUPRIE, B.,
COMRE,
A., SAME-EKOBO, A., TRIBOULEI’,
J.,
PUEL,
V.,
PIQUEMAL, A.
&
&PERT,
C. (1986). Epidémiologie des filarioses (onchocercose et bancroftose) dans la région de Tala-Mokolo
(Monts
Mandara-Nord Cameroun).
Bulletin de
la
Société de Pathologie Exotigue,
79,
755-765.
~IOREAU,
J.
P., PROST, A.
&-
PROD’HON,
J.
(1978). Essai de normalisation de la méthodologie des enquêtes
clinico-parasitologiques
sur l’onchocercose en Afrique de l’Ouest.
Médecine Tropicale,
38,
43-5
1.
MOYOU.SOMO,
R., ENYONG,
P.
A.,
FOBI,
G.,
DINGA,
J.
S.,
LAFLEUR,
C.,
AGNAMEI’, P.,
NGOSSO,
A.
&
MPOUDI
NGOLLE,
E.
(1993). A study of onchocerciasis with severe skin and eye lesions in a
hyperendemic zone in the forest of southwestern Cameroon: clinical, parasitologic, and entomologic
findings.
Ainerican Journal
of
Tropical Medicine aiid Hjgiene,
48,
1419.
NGOUMDU,
P.,
WALSH,
J.
F.
&
MACE, J.-M. (1994). A rapid mapping technique for the prevalence and
distribution
of
onchocerciasis: a Cameroon case study.
Annals of Tropical Medicine and
Parasitology,
88, 463-474.
PABOT
DU
CHATELARD,
P.,
STÉVENY,
J.
&
AURENCHE,
C.
(1978). Enquête onchocercose dans le Margui-
Wandala. In
Proceedings
of
the
12th
Conjiérence Technique de
I’OCEAC,
pp. 246-262. Yaounde:
Organisation de Coordination pour la Lutte Contre les Endémies en Afrique Centrale.
PROST,
A.,
HERVOUET,
J.
P.
&
TWLEFORS,
B.
(1979). Les niveaux d’endémicité dans l’onchocercose.
Biclletin
of
the World Health Organization,
57,
655-662.
REMME,
J.
H.
F.
(1995). The African Programme for Onchocerciasis Control: preparing to launch.
Parasitolog), Todaji,
11,
403-406.
REMME,
j.,
BA,
O.,
DADZIE,
K.
Y.
&URAM,
M.
(1986). A force-of-infection model for onchocerciasis and
its applications
in
the epidemiological evaluation of the Onchocerciasis Control Programme in the
Volta River basin area.
Bulletin
of
the
World
Health Opgaizization,
64,
667-681.
REMME,
‘J.,
DADZIE,
K.
Y.,
ROLLAND, A.
&
THYLEFORS,
B.
(1989). Ocular onchocerciasis and intensity of
infection in the community.
I.
West African savanna.
Tropical Medicine and Parasitology,
40,
340-347.
RIPERT,
G.,
RIEDEL,
D.,
YANG, R.,
FOUDA
ONANA, A.
&
ZIMFLOU,
I.
A. (1977). Etude épidémiologique de
l’onchocercose dans
cinq
villages de la vallée de la Sanaga (Cameroun).
Bulleth de la Société de
Pathologie Exotique,
70, 178-186.
ROLLAND, A.
&
BALAY,
G.
(1969).
L’onchocercose dans le foyer Bisa.
Mimeographed document
1111
ONCHO. Bobo-Dioulasso: Organisation de Coordination et de Coopération pour la Lutte contre les
grandes Endémies.
ST~VENY,
J.,
MALOSSE,
D.,
APPRIOU, M.,
TRIBOULEY,
J.,
ENYONG,
P.,
SAME EKOBO, A.
¿Q
RIPERT,
C. (1981).
Etude épidémiologique de l’onchocercose chez les Matakams des Monts du Mandara (Nord
Cameroun).
Bulletin de la Société de Pathologie Exotique,
74,
197-207.
TAYLOR,
H.
R.,
DUKE,
B.
O.
L.
&
MUNOZ, B. (1992). The selection of communities for treatment
of
onchocerciasis with ivermectin.
Tropical Medicine and Parasitolog)i,
43,
267-270.
WORLD
HEALTH
ORGANIZATION (1991).
Strategies
fir
Ivermectin Distriblition
through
Primaiy Health Care
Sjcsteins.
Document WHO/PBL/91.24. Geneva: WHO.
WORLD
HEALTH
ORGANIZATION (1995).
Onchocerciasis and
its
Corztrol.
Report
of
a
WHO
Expert Committee
on
Onclzocerciasis
Control.
Technical Report Series
No.
852. Geneva: WHO.
