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Country-wide rapid epidemiological mapping of onchocerciasis (REMO) in Cameroon

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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 > or = 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.
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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
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);
(:
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
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... Indeed no MDA was ever implemented in the eight Regions surveyed to control LF at the outset of this study. However, as onchocerciasis was shown to be widely distributed in Cameroon-all the Regions are affected with more than 6 million people infected [27,28]-ivermectin was already distributed since 1992 (up to 22 annual rounds in some areas) as part of community interventions. It was shown that mf rate and intensity for LF infections were quite low in villages regularly treated for many years with ivermectin as compared to untreated villages [29]. ...
... These data allow the national program to implement MDA only in those health districts where loiasis is not co-endemic or where community directed treatments with ivermectin (CDTI) had already been ongoing for onchocerciasis control, although loiasis is coendemic. Indeed, onchocerciasis maps were realized using the rapid epidemiological mapping strategy [27,[32][33], and loiasis map drawn [24] in support to onchocerciasis and LF control or elimination programs. In areas free for loiasis and where LF is endemic (ICT rate 1%) and onchocerciasis meso-endemic (20-40% nodules prevalence or 40-60 mf prevalence) or hyperendemic (nodules prevalence > 40% or mf prevalence > 60%), annual treatments (ivermectin in combination with albendazole) are distributed to all eligible population. ...
Article
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Background Lymphatic filariasis (LF) is one of the most debilitating neglected tropical diseases (NTDs). It still presents as an important public health problem in many countries in the tropics. In Cameroon, where many NTDs are endemic, only scant data describing the situation regarding LF epidemiology was available. The aim of this study was to describe the current situation regarding LF infection in Cameroon, and to map this infection and accurately delineate areas where mass drug administration (MDA) was required. Methodology The endemicity status and distribution of LF was assessed in eight of the ten Regions of Cameroon by a rapid-format card test for detection ofW. bancrofti antigen (immunochromatographic test, ICT). The baseline data required to monitor the effectiveness of MDA was collected by assessing microfilariaemia in nocturnal calibrated thick blood smears in sentinel sites selected in the health districts where ICT positivity rate was � 1%. Principal findings Among the 120 health districts visited in the eight Regions during ICT survey, 106 (88.3%) were found to be endemic for LF (i.e. had ICT positivity rate � 1%), with infection rate from 1.0% (95% CI: 0.2–5.5) to 20.0% (95% CI: 10–30). The overall infection rate during the night blood survey was 0.11%(95% CI: 0.08–0.16) in 11 health districts out of the 106 surveyed; the arithmetic mean for microfilaria density was 1.19 mf/ml (95% CI: 0.13–2.26) for the total population examined. Conclusion/significance ICT card test results showed that LF was endemic in all the Regions and in about 90% of the health districts surveyed. All of these health districts qualified for MDA (i.e. ICT positivity rate � 1%). Microfilariaemia data collected as part of this study provided the national program with baseline data (sentinel sites) necessary to measure the impact of MDA on the endemicity level and transmission of LF important for the 2020 deadline for global elimination.
... Rapid Epidemiological Mapping of Onchocerciasis (REMO) surveys conducted in Cameroon in the early 1990s showed that onchocerciasis was a country-wide public health problem with an estimated 12 million people at risk [9,10]. The Ministry of Health (MoH) started the community-directed treatment with ivermectin (CDTI) strategy in the West Region in 1996, initially with the support of The Carter Center, Lions Clubs International Foundation (LCIF) and the African Programme for Onchocerciasis Control (APOC) and then Sightsavers [11,12]. ...
Article
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Background Massangam health district (HD), in the West Region of Cameroon, has received ivermectin mass drug administration (MDA) for 20 years, however there is evidence of continued high transmission of Onchocerca volvulus. In order to better understand the transmission dynamics in the HD and inform intervention strategies there is a need to delineate the boundaries of the suspected area of high transmission within the wider transmission zone. Methodology/Principal findings Parasitological and entomological surveys were conducted to map out the breeding sites of Simulium damnosum and evaluate the prevalence of onchocerciasis in neighbouring communities, including Makouopsap sentinel community. Potential rapids were prospected for identification of S. damnosum larvae and black flies collected to determine infectivity rates. Adults were assessed for the presence of O. volvulus microfilariae through a skin snip biopsy and examined for the presence of nodules. Anti Ov-16 antibodies were tested for in children. Four perennial breeding sites were identified on the Rivers Mbam and Nja. Large number of flies were collected along the River Mbam, especially in the rainy season, with up to 955 flies per day, suggesting this river is a perennial source of black flies. A total of 0.8% of parous flies were infective across the study area. Parasitological studies provided evidence of high rates of infection in the sentinel community and three neighbouring communities, with 37.1% of adults microfilariae positive in Makouopsap. High Ov-16 seropositivity in children also provided evidence of recent on-going transmission. In comparison, communities sampled further away from the sentinel community and neighbouring breeding sites were much closer to reaching onchocerciasis elimination targets. Conclusions/Significance This study provides evidence of a particular geographic area of high transmission in an approximate 12 km range around the sentinel community of Makouopsap and the neighbouring breeding sites on the River Nja. To eliminate onchocerciasis by 2025, there is a need to explore alternative intervention strategies in this area of high transmission.
... Rapid Epidemiological Mapping of Onchocerciasis (REMO) surveys conducted in Cameroon in the early 1990s showed that onchocerciasis was a country-wide public health problem with an estimated 12 million people at risk [9,10]. The Ministry of Health (MoH) started the community-directed treatment with ivermectin (CDTI) strategy in the West Region in 1996, initially with the support of The Carter Center, Lions Clubs International Foundation (LCIF) and the African Programme for Onchocerciasis Control (APOC) and then Sightsavers [11,12]. ...
Article
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BACKGROUND: Massangam health district (HD), in the West Region of Cameroon, has received ivermectin mass drug administration (MDA) for 20 years, however there is evidence of continued high transmission of Onchocerca volvulus. In order to better understand the transmission dynamics in the HD and inform intervention strategies there is a need to delineate the boundaries of the suspected area of high transmission within the wider transmission zone. METHODOLOGY/PRINCIPAL FINDINGS: Parasitological and entomological surveys were conducted to map out the breeding sites of Simulium damnosum and evaluate the prevalence of onchocerciasis in neighbouring communities, including Makouopsap sentinel community. Potential rapids were prospected for identification of S. damnosum larvae and black flies collected to determine infectivity rates. Adults were assessed for the presence of O. volvulus microfilariae through a skin snip biopsy and examined for the presence of nodules. Anti Ov-16 antibodies were tested for in children. Four perennial breeding sites were identified on the Rivers Mbam and Nja. Large number of flies were collected along the River Mbam, especially in the rainy season, with up to 955 flies per day, suggesting this river is a perennial source of black flies. A total of 0.8% of parous flies were infective across the study area. Parasitological studies provided evidence of high rates of infection in the sentinel community and three neighbouring communities, with 37.1% of adults microfilariae positive in Makouopsap. High Ov-16 seropositivity in children also provided evidence of recent on-going transmission. In comparison, communities sampled further away from the sentinel community and neighbouring breeding sites were much closer to reaching onchocerciasis elimination targets. CONCLUSIONS/SIGNIFICANCE: This study provides evidence of a particular geographic area of high transmission in an approximate 12 km range around the sentinel community of Makouopsap and the neighbouring breeding sites on the River Nja. To eliminate onchocerciasis by 2025, there is a need to explore alternative intervention strategies in this area of high transmission.
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Onchocerciasis is a Neglected Tropical Disease that has a significant socioeconomic impact, especially in Sub-Saharan Africa. Numerous reports indicate that the Expanded Special Project for the Elimination of Neglected Tropical Diseases needs novel diagnostic tools before achieving its goal of successful elimination of onchocerciasis in Africa. The current diagnostic tests are either invasive, insensitive, or not applicable in the field and about 25% of persons infected cannot mount immune responses against the single antigen used in the only approved Ov-16 serological test. In the quest to identify novel biomarkers that can be used to certify that a patient is free from the disease, evaluate the progress of elimination programmes, and conduct post elimination surveillances, mass spectrometric analysis of Onchocerca volvulus crude extract revealed that 1392 proteins are expressed in the adult and microfilariae stages of the parasite. Computational analysis predicted six of the proteins as O. volvulus potential diagnostic targets. Linear B-epitopes were predicted from the six proteins and used to construct a multiepitope antigen (OvMCBL02). Serological analysis revealed that the OvMCBL02 test significantly differentiated between serum samples of onchocerciasis patients from the Kombone Health Area in the South West Region of Cameroon (n = 63) and control serum samples from Rwanda (n = 29) and Europe (n = 26) as well as between serum samples from the onchocerciasis hyperendemic region of Kombone Health Area (n = 63) and the hypoendemic region of Bandjoun Health District (n = 54). Interestingly, the test did not cross-react with serum samples from patients suffering from related nematode infections, thereby suggesting that further characterization of the OvMCBL02 multiepitope antigen will render it an additional member of the diagnostic toolbox for the elimination of onchocerciasis.
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A simple force-of-infection model for onchocerciasis has been developed for a study of the age-specific epidemiological trends during a period of vector control in the Onchocerciasis Control Programme in the Volta River basin area (OCP). The most important factors included in the model are the longevity of an infection, the aspect of super-infection, age-specific exposure, and the intensity of transmission during the pre-control period. The aim of the study was to determine the most appropriate statistics for the epidemiological evaluation in the OCP. There was generally good agreement between the epidemiological trends, predicted by the model, and the observed trends in the prevalence and mean load of microfilariae in skin snips taken from a cohort population from 23 villages in an area with 8 years of successful vector control in the OCP. It is concluded that the epidemiological trends during the control period are not uniform but depend on the initial age and the initial endemicity level of the population. The epidemiological indices for cohorts of children, born before the start of control, will not show a decrease during the first 8 years of interruption of transmission. The prevalence is too insensitive to be useful for the evaluation in hyperendemic villages during most of the control period. The most sensitive and meaningful statistic for a comparative analysis and for the assessment of epidemiological changes is the geometric mean microfilarial load in a cohort of adults. This index, which is called the Community Microfilarial Load (CMFL), is now routinely used in the OCP. The new analytical methodology has enabled a much better appreciation of the significant epidemiological impact of 8 years of vector control in the OCP. Several related aspects of the pre- and post-control dynamics of onchocerciasis infection are also discussed and priorities are formulated for further work on applied modelling of onchocerciasis.
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The study carried out in five villages in the Sanaga Valley of Cameroon was concerned with the prevalence of the disease, the level of infection and an evaluation of the effect of the parasites on the health of the people. Entomological data were also collected. The study was concerned with the onchocerciasis found in the forest area where the disease is hyperendemic. The males are infected moreoften than the females. Among the adults the skin and lymphatic lesions are extremly important. It was found that as the visual acuity diminishes with age, from age forty many for the people are blind. The villages most affected are those situated near the Sanaga rapids where there is a concentration of the breeding sites of the vectors.
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In order to be able to compare in time and space the results of onchocerciasis surveys in West Africa, the authors suggest to standardize the methodology of these surveys. The following points are defined : criteria to choose the villages, selection of population specimen, registration of socio-demographic data, clinical examination, assessment of visual acuity, parasitological examination founded on two quantitative bloodless cutaneous biopsies, definition of epidemiologic indices, adjustement of these indices to a standard population, synthesis of results by age-group and sex on the one hand by the presentation of frequency distribution of cutaneous microfilarial densities, on the other hand by calculation of geometric means of these densities.
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In areas endemic for onchocerciasis, active community-based treatment with ivermectin is preferred to individual diagnosis and treatment. Ideally, all infected persons should be treated, although initially priorities may have to be set at local or national levels. We suggest that all communities with a prevalence of O. volvulus infection of 20% or more in adult males aged 20 years or over should be treated; and that elsewhere facilities for passive treatment should be provided. In some areas, for logistical reasons, treatment may first have to be started in communities with the highest prevalences (perhaps above 40% or even 60%) and then expanded to all endemic communities. The available data suggest that a rapid assessment method based on the examination for nodules will give a simple, acceptable, non-invasive and reasonably reliable method of identifying the communities that should be treated. If a nodule is detected in at least three men from a sample of 30 men aged 20 years or over, the community can be assumed to have a true prevalence of infection of 20% or more and should be included in community-based treatment.
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A method is introduced for the analysis of community patterns of ocular onchocerciasis in relation to the intensity of infection as measured by the Community Microfilarial Load (CMFL). Specific features of this method are the clear definition of ocular lesions and their separation into early and advanced stages, and the estimation of the prevalence of onchocercal blindness after exclusion of other causes of blindness. The method is applied to the ophthalmological and parasitological data from 33 villages from the West African savanna in order to obtain a reference pattern for subsequent analyses of ocular onchocerciasis patterns from other bioclimatic zones. In the savanna, there exists a clear linear relationship between most indices of ocular onchocerciasis and the CMFL. Mean ocular microfilarial loads, prevalences of the advanced lesions of the anterior and posterior segment of the eye and prevalences of different classifications of blindness show a high degree of correlation with the CMFL, as does also early sclerosing keratitis. The correlation is poor for the other early ocular lesions. All relationships are similar for the two sexes with the exception of posterior segment lesions which remain more common in males after correction for intensity of infection. The CMFL is superior to the prevalence of microfilariae in the skin as an index of endemicity. It allows a good prediction of the severity of onchocercal ocular disease in savanna communities using parasitological information only.