WORLD HEALTH ORGANIZATION AFRICAN REGION
ORGANISATION TVIONDIALE DE LA SANTE REGION DE L'AFRIQUE
ONCHOCERCIASIS CONTROL PROGRAMME IN WEST AFRICA
PROGRAMME DE LUTTE CONTRE L'ONCHOCERCOSE EN AFRIQUE DE L'OUEST B P. 549 OUAGADOUGOU, Burkrna Faso Télégr . ONCHO OUAGADOUGOU
:34 29 53 - 34 29 59 - 3429 60 Télex. ONCHO 5241 BF Fax' 34 2875
REPORT OF OCP ACTIVITIES AND THE ENTOMOLOGICAL RESULTS IN THE OUEME
Samuel A. SOWAH* and Hyacinthe AGOUA*
Under contractualservice agreement
firstversion of this report was written by
MrS.A. Sowah for the period 1978-1998.
The document was reviewed and updated by Dr. Hyacinthe
AGOUA until2001, withthe collaboration of the Programme Director and the Chiefs of Units.
*MedicalEntomologists. Previously WHO-Oncho control Programme staff members
Ouagadougou, June 2002
2. OVERVIEW OF THE ONCHOCERCIASIS CONTROL PROGRAMME IN WEST AFRICA
DESCRIPTION OF THE OUEME BASIN AREA
ENTOMOLOGICAL ACTIVITIES (EVALUATION AND VECTOR CONTROL)
4.2.3.Insecticides used (Insecticides rotation) 4.3.
4.3.1 4.3.2 4.3.3 4.3.4 4.3.5
Special studies on S. soubrense Beffa form.
Entomological results on 3 1 -12-2001.
SURVEILLANCE OF AQUATIC FAUNA EPIDEMIOLOGICAL EVALUATIONS
6.1. Epidemiologicalresults before
during vector control.
9. POPULATIONS SENSITIZATION AND MOBILIZATION ACTIVITIES
This report is written as a result
ofcontractual service agreement entered into
of thisreport is
togive a consolidated account
wellas the results obtained from the beginning of OCP activities to date.
The report should cover not
onlyentomological activities but also
ofOCP activities such
carried out (with theircorresponding
results),Ivermectin clistribution. sociological investigations
ifany, sensitisation carried
field staff.and any other relevant inforrnation available.
2. OVERVIBW OF THE ONCHOCERCIASIS CONTROL PROGRAMME IN WEST AFRICA
in West Africastarted
its activities in 1974and
Mali, Nigerand Togo).
Itsoriginal savannah area covered 654,000 km2.
form ofonchocerciasis resulting in blindness prevailed leading to the depopulation
tlre Programme activities
d'Ivoire in1978-lg7g, the Programme area covered
764,000km2,which represents about 18,000 kms of rivers treated.
Inview of the good results obtained and
to prevent reinvasion, furtherextensions
and westwards in1987-1988.
Currently, the Programme concerns 11 countries (Benin, Burkina Faso, Côte
d'Ivoire,Ghana, Guinea, Guinea-Bisau.
Mali. Niger,Senegal, Sierra Leone and Togo) and covers 1,300,000 t<m'z 1fig.
The Prograrnme aimed at
controllingonchocerciasis to ensure that
thisdisesase is no longer a
tosocio-economic development, and also
thatcountries involved are able to perpetuate this realisation.
On the administrative level, theHead
Office of theOnchocerciasis
ControlProgramme ls based
inOuagadougou, Burkina Faso and includes the Administrative
Unit,the Planning, Evaluation and Transfer
Unit,and the Vector Control Unit.
On the operational level. the
Vector Control Unit is divided into two(Eastem and Western) zones
withsectors, sub-sectors and operations bases
through a radionetwork,
which allows a rapidtransmission
ofepidemiological data as
scientificand administrative directives.
In1990. there were
5sectors,20 sub-sectors and one antenna
and itssouthern extension.
counts 8 sectorsand 25 operations bases.
The Administration Board is the Joint Programme Committee (JPC) thatincludes representatives
of programme countries, Sponsoring Agencies and delegates of 23Donor Organisations
(WHO)that is the implementing agency
ofthe programme, the Food and
(FAO)the United Nations Development Programme (LINDP) and the World Bank.
As from themid-9Os,
andoperations bases were closed
tothe gradual reduction
activities in view of thesatisfactory results obtained
inmost river basins. OCP activities
3. DESCRIPTION OF THE OUEME BASIN AREA
The entireOueme basin
lies in theRepublic
of Benin. Itstretches
from latitude10 degree
into the Gulf of Beninat the coast
of Benin (fig. l), ina woody
Savannah area known as the Dahomey Gap, where the Savannah type
ofvegetation stretches from the
rightto the coast.
namely therainy season and the
in theSouth around late
mid May to midJune. The
rainyseason ends around
inthe Harmattan, which marks the beginning of the dry season.
ofthe Oueme are: the
Yerou Maro,the Wewe and the
North. Inthe middle portion are the
Adjiro. Inthe South are the
Okparaand the Zou.
Generally, the main
riverand its tributaries
flow mainly inthe
withthe peak around the month
Fromlate October to the
middle ofNovember most
ofthe tributaries stop
river,however, continues to
flowup to the middle of January.
of theOueme can
be more than1000
Thiswas recorded in week 36
On the tributaries the discharge can be around 500 cubic metres per second. This was recorded at Atcherigbe on the Zou
in1999 in week 35
In the dryseason,
theentire basin dries
up with no flow at all from the North to thearea around Zagnanado where
minor flowcan be observed. Eventually these
flowsalso stop a month or two before the onset of the rainy season.
river and its tributaries are devided intoseveral stretches,
according tothe irnportance of the tributaries and the discharge, -OU
100, OU 400...etc.
(EVALUATTON AND VECTOR CONTROL)
4.1 Entomologicalsurveillance 4.1.1.
.ln order to make the work easer for the Aerial Operations team, nver sfrefches are coded by taking into account, the name of the river basin and adding a number from 100 to 900.
For example : OU 100 and OU 400 means: Oueme nver, stretches : 100 and 400.
from lat. 9degrees
40minutes north, a
point tothe confluence of the Yerou Maro, six other important breeding points can be found
Eleven other major breeding points are found
(lat.9 degrees 13 minutes North) to the confluence
ofthe Odola (lat. 8 degrees 46 minutes north). Note that these points are identified
only inlatitudes because
ofthe fact that the Oueme
flows virtually from North toSouth, hence, the latitudes pinpoint to a particular point on the
river.From the confluence of the Odola to the Atchakpa breeding point, eleven other major breeding points can be identified.
The main complex breeding points on the Oueme are found between Atchakpa catching
point. At thisstretch
(from lat.8 degrees north
to lat. 7degrees 29 minutes north), the breeding points are
withvery few pools in-between.
Below the Atchakpa-Aguigadji stretch apart from the complex breeding
practically, nonatural breeding
points. On theother hand occasionally man made fish traps can be found here and there
Very few breeding points are found on the Alpouro, which are not important forS.damnosum s.l. breeding.
On the Yerou Maroalso
very few S.damnosum
points are found. Theonly important breeding point is found near its confluence
notmany and are
forS. damnosum s.l breeding.
There are very
fewbreeding points on the upper stretches
ofthe Terou, where the
North toSouth. The important breeding sites are located frorn the confluence
Aguimoto the confluence of the Terou
One important breeding
minorbreeding points are found upstream but these do not play important role
inS. damnosum s.l breeding because of the short duration of
flowof this tributary.
The uppermost breeding
lat.8 degrees 48 minutes
are no breeding points down to lat. 8degrees
39 minutes north. From this point down tothe confluence
withthe Oueme twelve important breeding points can be found.
Itis important to note that S. soubrense Beffa form is named after this
riversince this specie was
firstdiscovered on this
principalbreeding points about
2degrees East and2 degrees
l5minutes East around latitude 8 degrees 29 minutes North.
Among allthe tributaries
ofthe Oueme, the Okpara
tributary withthe greatest number breeding
points, for, atleast, about one hundred and eighteen
pointscan easily be identified. The
majorityof these are found between lat. 9 degrees 4 minutes
the Republic ofBenin and Nigeria. The rest of the breeding points (about
thirty-eight innumber) are entirely found
inthe Republic of Benin.
entirely inthe Republic
of Beninand takes
lat. 8degrees 27 nrinutes
into theOueme around
lat. 7degrees near a
village called Gongbe.
TheZouis considered to be one of the longest tributaries of the Oueme but has
long tributary. Theprincipal breeding points, twenty-one in number, are situated between latitudes 7 degrees 35 rninutes
Northand 7 degrees 20 minutes North.
point on lat. 7degrees
North. no morenatural breeding
pointsoccur, except one
or twoman made
littleat this stretch
of lot ofgreen algae
Kouffo is nota
tributary ofthe Oueme.
It isa coastal
in Togo inthe legion of Dotoé on the east of the "Okéloukoulou Rocs" and enters into the Ahémé Lake in Benin.
twostretches: the stretch OU801, upstream Lanta that
withbreeding sites, and the stretch OU802 that is downstream Lanta.
ofcatching points on the Oueme
itselfalong the years had been
six.These are; Beterou. M'Betekoukou, Atchakpa,
Affon, Aguigadji.and Zagnanado,
firstcatch was made at
of Natitingou inOctober
1976.Thepoint was then passed on to the Parakou Sub-sector after the creation
pointhas therefore been under
point onthe Oueme, is regularly used as monitoring point to date.
Atchakpa was created
firstcatch was made at this point in the rnonth of December 1978, and is being used regularly to date.
M'Betekoukou has a
similar history likeAtchakpa.
in1978 and the
firstcatch was made
inthe month of November 7978, and
is stillbeing used as a monitoring point
todate. This point was
firstunder the Parakou Sub-sector but passed on to the Bohicon Sub-sector
firstcatch was made
inJanuary 1979. This
pointwas used regularly
until Aplil1986. Catching was stopped because
lowcatches registered at
this pointand also because
In1987 OCP had
totake strong economic measures
withinthe budget. because
offunds. There was therefore reduction
in VCU (VectorControl
Thisreduction affected certain number
was one of them.
in1982 and the
firstcatch was made
inSeptember 1982. The point was
flrstunder Parakou Sub-sector
butlater on transfemed
in1982. Since its creation
Aguigadjihas been a regular catching point to date.
This pointwas created
regularly used fromSeptember 1982
untilSeptember 1987. because
of similarreasons already rnentioned under
firstcatch was made at Barerou
in1982 and has been used regularly to date.
Wari Maro 2705
The only catching point on the Terou wascreated
and first catch wasmade
inNovember same year, and has been used regularly as a monitoring point to date.
Like Wari Maro, theBanon
It is the onlycatching
firstcatch was made in November in the same year and has been used regularly to date.
Vossa was created
firstcatching made in November and
is stilla monitoring point to date.
Created in June 1978 and used regularly
Kaboua was created
firstcatch was made
inNovember same year and has been used regularly to date.
The point was created
firstcatch was made in June 1978 and is
stillbeing used as
rnonitoring point to date.
Okeo was created
inJune the same year.
Itwas used as a regular monitoring point
Tlre Zou has three catching points, namely. Atcherigbe, Zoudli and Cove.
The point was created
in1978 and was under the Sub-sector
ofParakou. but transferred to the
in 1982 after the creation of thisSub-sector.
The first catch was made inNovember 1978 and has since been a regular catching point to date.
Cove was created
in1982 and was under the Bohicon Sub-sector. The
firstcatch was made
in August 1982.Itwas a regular catching
point untilOctober 1987 when catches were stopped
forthe same reasons given under
in1982 and was a regular catching point
of it's low flycount.
The hrstcatch was made
in1984 catches were drastically reduced.
Afterthat year, no catches were made
until1989 when only three months catches were made and one month
Lanta (code 3001)
Catches were made atLanta
to1999 Konfopka (code 3008)
This point is located upstream of Lanta. Catches were made between 1995
Several entomological helicopterprospections
were carried out on the Oueme andits tributaries
forvarious reasons. Among these were the
intosuspected treatment failure.
b) Toinvestigate the problem
valley byS. soubrense
from neighbouring Nigerian rivers.
c)For, purely research reasons
d)For. Operational reasons
4.2.1. Aerial larvicidins
Aerial larvicidingbegan in the Oueme basin
inweek 12, 1987.
untilweek 18, then treatment
to lack of flow.Vectobac*
Treatment was resumed
inweeli 36 and continued
for sixcycles, namely,
fromweek 36 to week 41.
The larvicide used this time was temephos (Abate@).
Itis interesting to mention that,
only13 treatment cycles had been carried out
Infact the "attack phase"
of larviciding inthe Oueme basin started
in1988 on week 9
of1987 can be considered as treatment trials.
tonote that the period
aim of thiswas
toeliminate the S. damnosum s.1. population at
focibefore the onset of the
Inso doing, economy could be made
rainyseason by treating shorter stretches of the
riveror suspend treatment in view of good results, namely, absence
This theory was however, dashed because
ofinvasion or contamination of the Oueme basin by S. soubrense Beffa form
fromneighbouring rivers in Nigeria.
Since the "attack phase"
in1988, aerial operations have continued uninterrupted
inthe Oueme basin
Aerialoperations are suspended
dryseason when the entire basin dries up (see section 2 paragraph 7 of this report).
fora minirnum treatment
inthe Oueme basin
fora given year is between weeks I
period lbra maximum treatment
with thepeak, occurring between, weeks 36 to 40.
These treatment cycles correspond to the pattem of discharge of the Oueme and
it'stributaries during a given year as already mentioned.
The treatment cycles
ofthe Oueme basin including the Okpara, the
to2001 are in the annex of this report (tables
7.2,3, 4. 4a, 4b and 4c).
4.2.2. Ground larvrcldrug
larvicidingis not used in the Oueme basin as the main method
ofvector control but as
support to aerial
larvicidingin the case of treatment failure due to bad passage
of larvicidesor when a breeding site is missed after the passage of an aircraft.
Itis also used
dryseason on certain isolated breeding points
tominimise treatment cost
lowdischarge in the dry season when aerial
difficultto carry out, ground
larvicidingis again ernployed.
This is usually between weeks 1 to week 8 on the tributaries
larviciding iscarried out
bythe various Sub-sectors
ofex Parakou Sector. depending on the location of the points to be treated.
4.2.3.Insecticides used (insecticides
allthe insecticides employed by the Programme (Abaten',
B.t.H-14, both Vectobac* and Teknarc',
phoxim,chlorphoxim, pyraclofos, permethrin, carbosulfan and etofenprox) are being used on rotational basis in the Oueme basin.
The reasons for the rotation of insecticides are as
1. Toprevent the occurrence
if onlyone insecticide
isused, as occurred
inthe early stages of the Programme.
Inorder to avoid this, the consecutive use
ofinsecticides belonging to the same chemical compound is discouraged to prevent cross-resistance.
2.The rotation is also carried out
forthe cost-effectiveness of treatment. Using B.t. H-14 at very
willrequire a huge volume
This willmean a requirement
of a lot offèrry time
foran aircraft and loading. On the other hand an insecticide
likepermethrin which is
verysmall volume at very high discharge. thus a small amount can cover a
lot of riverstretch to be treated.
3. Rotation ofinsecticide
toxicity of theinsecticide
B.t. H-I4 whichhas a
very low toxicity onnon- target organisms is used at
from Icubic metre per second
toabout 35 cubic metres per second. While permethrin and carbosulfan,
onlyused when the discharge
ishigher than 70 cubic metres per second and cannot be used
ina given year. Pyraclofos is used at a discharge
of15 cubic metres per second onwards, and this applies to etofenprox also. On the other hand, insecticides
likeAbate@, phoxim. and chlorphoxim, which have relatively
low toxicity.can be used even at
4. Finallyrotation is carried out according to the carry
ofthe insecticide. B.t.
a lot oftreatment
for highdischarge treatment because the volume
willnot be cost effective as pointed out earlier on. However an insecticide
whichhas a very good
with its low toxicity onnon-target organislns can be used
at almost anydischarge.
isanother insecticide, which has a very good carry but because
toxicityas indicated earlier on,
from15 cubic metres per second upwards.
The practical aspect of the rotation
ofinsecticides can be seen on the tables of treatment of the Oueme basin in the annex of this report (tables
In theOueme basin, resistance
totemephos had been
resistance was detected at the
LowerOueme area around
(OU700), Atchakpa (OU 600). the Upper Oueme around
Affon (OUl04),and the Upper Okpara around Bassa
OU 720). The susceptibility totemephos became
normal in 1998.See
graph on"Resistance to temephos Zone East"
the vectors involved in theOuerne
basin, adult flies are caught byvector
collectors as described
al.(1978) and are separated
into differentgroups, through their
wing tuftexamination using
method.These groups are classif,ted as
04. and 05.
The 01groups are
all the individualhairs
wing tuftare pale. The 02 groups are the ones
majority of individualhairs
fewdark hairs (less than 50% of the total numbers of the
wing tufthairs). These
twogroups are considered to belong to the savannah group
ofspecies, namely, S. damnosum s.s. and S. sirbanum.
The 03 groups are the ones
in which50oÂ are pale hairs and 50oÂ are dark hairs. These can be savamrah species
be S.soubrense. These are however rare in the Oueme basin.
The 04 groups are those
majority ofthe hairs on the
wing tuftare dark. The 05
groups are those with 100% dark wing tuft hairs.These
two groups are the forestspecies, S.
sanctipauli or S.soubrense
falthough ithas been
pointed out thatsome members
of adultflies rnorphologically
lookingS. soubrense Beffa form have pale
wing tufts(Garms 1978 and Meredith er
al1983.). these have disappeared after the 1983 drought ( Cheke et
From available data
forboth adult population and larval population, the dominant species on the tributaries
isS. damnosum s.s. On the other hand, on the Oueme South
pointthe dominant species during the major part
isS. soubrense Beffa
form.See graphs on
MBR (Monthly BitingRate) on seasonal variation
Beffa format Atchakpa,
Aguigadjicatching points. These
twographs are obtained
from1980 to 2001
(fig.13, 14, and 15).
No S. sanctipauli and S.)rahense
have ever been found in theOueme
basin, eitherby cytotaxonomy or by adult morphological examinations (table 5).
The parasite involved
Since the creation
ithas been shown that the
majority of theparasites transmitted
theSavannah strains. Occasionally some forest strains are also transmitted.
Itis important to note that these Savannah strains are transmitted
flies(S. damnosum s.s. and S. sirbanum). and the forest
From the tables
ofthe Annual Transmission Potential
(ATP)and the graphs
of ATP forboth the Oueme and
it'stributaries. the pre-control data showed that transmission was
very highon both
for allspecies combined were
M'Betekoukou(Oueme), and Atcherigbe (Zou). On the Okpara at Kaboua, the
slightlyover 8000 (tables 7
The other points
likeAtchakpa, Beterou and
Aguigadjion the Oueme had pre-control
less than 4000.
points of thetributaries,
like Wari Maro (Terou),and Vossa
(Beffa) thepre- control
ATPwas around 5000.
Affon(Oueme), and Barerou (Yerou Maro) had pre-control ATP
ofless than 1000.
Before vector control operations started, there was a severe drought
in1983, and the situation returned to normal after 1985. This drought affected both the pre-control
ABRsignificantly, as shown on the graphs of ATPs and ABRs
The transmission during the
to2001. The drought mentioned above greatly helped
to bringdown transmission
ATP ofabout 1000 as early as 1986. a year before aerial
only point whichhad
ATP ofmore than 1000 was M'Betekoukou,
withATP of more than 2000
In1994, after seven years of larviciding, the ATPs on all the points in the Oueme basin, except at Kaboua on the Okpara, had fallen
below1000. These results are exceptionally good, considering
the time involved. It ishowever important
from the drought factor,large-scale ivermectin distribution began in the Oueme basin
is by S.soubrense
of ATPs at the followingcatching
points, M'Betekoukou, Aguigadji,and Atchakpa. However, on the Upper Oueme at Beterou transmission
is mainly bySavannah species S.
damnosum s.s and S. sirbanum
Onthe northern tributaries
likethe Terou and
Yerou Maro,again S. damnosum s.s. and S.
sirbanum are the major transmitters;
ATPhistograms of Wari Maro and Barerou catching points show tlris clearly
Asone goes down south, transmission
byS. soubrense Beffa
formbecomes important on the tributaries
likeBeffa, Okpara, and the Zou
qn§. soubrenseBef for
Special studies on
Beffa formhad been carried
out intlre rainy season on the Oueme river and its tributaries
in1991 and 1992.
These studies had shown that the M'Betecoucou area was
importantcontamination was also observed around Kaboua
fromthe Nigerian border towards 'West
North,less or no contamination had been observed (frg.
4.3.5. EntomologicalResults on
In the Ouérné basin, out
of15 catching points regularly monitored
in 2001,three (3) showed a corrected ATP O. volvulus above 100. These points are M'Bétékoukou
with ATP :294:.
with ATP :210and Djabata
with ATP :261.
Allthese points are located near the nigerian border and are regularly re-invaded in the rainy season
byS.soubrense Beffa form.
Considering the transmission
bythe savanna species
of similium, only thecatching
Diabata (on the Okpara
ATPabove 100 which was 138.
Given the very high precontrol data
(ATPabove 2,000 at most catching points and 6.000
8.000 at M'Bétékoukou and Kaboua)
itcan be said that the entomological situation is
relativelygood in tlre Oueme
basin(tabl es J , 7
a,7b,et frg. 26 to 3 5).
5. SURVEILLANCE OF AQUATIC FAUNA
The chemical insecticides used by OCP are degradable and do not accumulate
inthe food chain.
to kill simuliumlarvae are
not toxic forhumans and mammals.
firstrequirement in the choice
Insecticides that meet these requirements are submitted
to thescreening procedure established by OCP Programme and its Ecological Group.
Thisindependant Ecological Group
whichincludes international Experts scientists analyzes the results to provide guidance to OCP monitoring and aquatic environment protection action.
National teams of hydrobiologists are in charge of the surveillance of aquaticfauna
(invertebrates and fish). See figure 36 for the location of aquatic fauna surveillance sites.
Most hydrobiologicalsurveillance stations
in Benin are located on theOuémé
M'Bétékoukou,Atchakpa and Bétérou. The stations on the tributaries are; Atchérigbé on the
ZoqKaboua on the Okpara, Vossa on the
Beffaand Lanta on
the Kouffo. The Béninnational hydrobiologists team, had undertaken monitoring at these sites
of thesurveillance stations
bythe Ecological Group and the financial
difficultiesof the Programme.
In1995, OCP consultants
didsome samplings at
the ichtyofauna, the twostations
regularly monitored were M'Bétékoukouand Bétérou on the Ouémé river.
ofCEU showed an increasing trend
forthe Bétérou station and
for the M'Bétékoukoustation.
confirmed bythe ponctual catches carried
noted in13 fishing sessions showed
atBétérou and 55 species at
M'Bétékoukou in16 samplings.
The fish inventory carried out in 1995 did not show thedisappearance
of any fishspecies because
of larviciding. However, itshould
of fish mortalityrelated
inlow waters were reported several times in the Ouémé basin.
ofaquatic entomofauna was not organized due to unfavorable hydrological conditions. Ponctual samplings carried out at Atchakpa and
not allow todraw any conclusion concerning the impact
oflarvicides on the fauna at these
whichshowed poor taxonomic abundance
AtBétérou, the taxonomic abundance
ofsaxicole fauna is more important than
twoother stations. On the contrary, the density
in1995 is lower compared to densities recorded
in1985 and 1986.
the whole,as the period
onOuémé was short,
possible to detect any effect
of larvicidingon the fauna in this river. But
fromobservations carried out on other
withthe same larvicides
itcan be envisaged that there
is noimpact on non- target aquatic fauna.
6. EPIDEMIOLOGICAL EVALUATIONS
6.1. Erridemiologicalresults before
ofthe epidemiological data,
forthe Oueme basin, can be found
tlris report (tables 8. 9, 10 and figures 37
The pre-control data for the epidemiological survey showed villages with veryhigh prevalence. The notable ones are villages on the Oueme
(CMFL)was also quite high in these villages, e.g.,
l. A village likeAbgagoule. code 3g2,hadprevalence
in March1979 (8
yearsbefore vector control),
with CMFL of16.74 mf/s, and prevalence
2. Agonlin Kpahou,code 5078, had prevalence
larviciding), with CMFL of13.91 mf/s. no
3. Atchakpa, code 3881, hadprevalence
in May 1978 (9 years beforeaerial
larviciding). with CMFL of23.51 mf/s and prevalence
larviciding), CMFL of19.59 mf/s, and prevalence
Koko.code 205, had prevalence
(9years before aerial
larviciding), with CMFL of36.79 mf/s. and prevalence
Idadjo.code 390, had prevalence
in March l9l9(8 years before aerial larviciding),
with CMFLof 28.89 mf/s. and prevalence
Banicri,code 315, had prevalence
inJune 1977 (10 years before aerial
larviciding), with CMFLof 24.80 mfls, and prevalence
Aguigadji,code 408/5083, had prevalence
of 8l.9yo in April1979
larviciding). with CMFL of33.31 mf/s, and prevalence
Wewe,code 316, had prevalence
(I0years before aerial larviciding),
with CMFL of12.72 mf/s, and prevalence
Zouvalley, epidemiological surveys had been carried
out atleast once
willbe used for this report. These
fourvillages are chosen because of their high pre-control prevalence.
1. Ferme Agbodjime,code 5076, had prevalence
inDecember 1989 (barely
larviciding). with CMFL of17.49 mf/s.
withno record on
Konkondji. code 395, hadprevalence
in March 1979 (8 years beforeaerial
larviciding), with CMFLof 24.56 mf/s, and prevalence blind of 2.3oÂ.
Zonto,code 400, had prevalence
of 695% in April1979 (S years before aerial
witlr CMFL of25.82 mf/s and prevalence
Avideme.code 5249, had prevalence
larviciding), with CMFL of20.16 mf/s. No
01the Terou-Oueme basin. surveys had been carried out at least once
inseven villages. The pre-control prevalence for these seven villages has a range
for twoof these villages, namely, Igbomakoro, code 386, and Sawoundi, code 387, the rest had been visited only once. These villages therefore
first visited in May1978
(9years before aerial
larviciding), with CMFLof 31.89 mf/s, and prevalence
(9years before aerial
larviciding), with CMFL of14.72, and prevalence blind of 0.60Â.
carried out in eight villages in the Kouffo valley.The pre-control prevalence was
not very highcornpared
villageKogbetohoue, code 401, where the pre-control prevalence was 60.4oÂ.
1979, the rest of the villages had prevalence of less than 50oÂ. The range is 6.7Yo to 46.50Â; (table 8).
For pre-control data of epidemiologicalsurveys
two villages arechosen
forillustrative prlrposes, and these are:
Kaboua,code 275, had prevalence
in May1978 (9 years before aerial
larviciding), CMFL of17 .52 mf/s and a prevalence
Woria,code 396, had prevalence
(8years before aerial
larviciding), with CMFLof 23.91 mf/s, and prevalence blind
durins Vector control.
thegood epidemiological results
riverand its tributaries are due to both vector control and ivermectin distribution.
followingvillages illustrate these results
Asalready shown the pre-control prevalence
for M'Betekoukouwas 78.0%
with CMFL of19.59
(78.8%). In1994 during the month of December the prevalence
with CMFL of0.41 mf/s.
Zoudji,code 5396, had a prevalence
with CMFL of4.75
In November 1995, the prevalence
with CMFLof only 0.44
with CMFL of17.45
Twoyears after ivermectin distribution, namely
fiveyears after vector control started, the prevalence
mf/s,and three years later, namely,
1995, the prevalence
with CMFLof only 0.88 mf/s.
6.3. Latest losicalresults
itself, the latest epidemiologicalevaluations
had been carried out inthe
1. Atchakpa.code 381/5880, which had pre-control prevalence
of l2.2yo,as already mentioned, now has prevalence
with CMFLof only 0.13 mf/s.
2. Idadjo, inFebruary 1998 has prevalence
with CMFL of only0.55
mfls,compared to 73.4%o as already mentioned.
3. Koko,in February 1998 has prevalence
of9.8Y" compared to 64.40Â in
April1999, has prevalence
April1999. has prevalence of only 0.6% compared
to 619% inJ:une 7977 .
6.3.2. Tributariesof the Oueme
Latest results of the villages on the tributaries of the Oueme,
like,Okpara, Zott, Terou and the
Kouffo.showed that the prevalence has
low. Insome areas
it isless than l0oÂ,
with CMFLof less than
Irnf/s. (tables 8, 9, 10 and
fig.38 to 41).
1. Konkondji;code 395;
inMarch 2000 had a prevalence
of1 .9oÂ and a
CMFL of0.08 mf/s compared to 72.40Â of prevalence in March 1979.
2. Wokpa;code 5038.
inDecember 2000 had a prevalence
with a CMFL of0.01 mf/s. compared
to54.8% of prevalence
CMFL of7.89 mfls.
3. Zouto:code 400,
inDecember 2001, had a prevalence
of1 .8% and a
CMFL of0.06 mf/s.
to69.5Yo of prevalence
in1979 as already mentioned.
1. Lanta; code423 inApril 1999,hadaprevalenceof0.60Â
compared to 42.70Â of prevalence in
2.Kogbetohoué; code 401; in february 1998. had a prevalence
CMFL of 0.47nfls.compared
InDecember 2001, an ophthalmological evaluation was carried
out in 06 villagesin the Oueme basin
of1987 people, 1365 were present.
Skinsnip was made on 1362 people and 1105 people aged 05 years and above underwent ophthalmological tests. This test concerned the anterior and posterior segments of the eye.
Results analysis showed
that skinand eye parasitisms had
ofrnicrofilariae load and number
ofcases. Indeed, the highest
microfilariaeloads were 377 at Zouto
in1987;66 at Okpa and 64 at Madengbé
in1995 compared to 22 at Okpa and I 1 at Madengbé
theeye lesions, the
63 at Zouto in1987; 19 at Madengbé
serious onchocerca eye lesions was noticed.
Allinflamatory lesions had regressed except two cases at Okpa. The highest microfilariae loads were recorded in this village (tables
islocated at the confluence
ofOueme and Okpara rivers close
to the borderbetween
Benin. It is known that the mediumOuémé and Okpara are re-invaded in the rainy season
byS. soubrense Beffa form coming from Nigeria.
Inconclusion, the ophtalmological survey carried out
inDecember 2001 revealed that there was a clear regression of eye onchocerciasis in the 06 villages surveyed.
inthe Oueme basin and the
Kouffo in1989. Nine villages were covered.
In1 990 in Zone 3, eleven ( 1 1 ) villages were covered
In1991 the Oueme area was again visited, this tirne covering 36 villages in Zone 3
In1992 the Lower and the Upper Okpara, as
MiddleOueme were visited, covering again 36 villages. also on the Agbado, the middle
Zot(Zote4), where 104 villages were covered.
In1993 the areas, where large-scale ivermectin
distribution tookplace were
Kouffo,Oueme and Okpara, where 415 villages were covered.
Inthe same year (1993) the Oueme and the
Zouwere visited. covering 347 vlllages. and on the
Kouffo187 villages were covered.
ht1994 the Agbado, the
MiddleZou had large-scale ivermectin distribution
villages; (Zone 4).
In1995, Zones 3 and 4 were visited again covering 349 vlllages.
Inthe same year, the Upper and
the MiddleOkpara (Zone
5)were visited, where 312 vrllages were covered.
In thesame year, Terou (Zone 6) was also visited covering 305 villages.
Itshould be noted here that,
of1996, the national mobile teams. headed by the national Co-ordinator carried
outlarge-scale ivermectin distributions,
localdistrict health units.
to2001. can be
found in table13
inthe annex of this report.
In January1997, the
villagecommunities were trained
to carry outlarge-scale ivermectin distribution themselves, this had therefore been the case since then.
8. SOCIOLOGICAL INVESTIGATIONS.
Atthe time of
writing,no sociological investigation had been carried out in the Oueme basin.
9. POPULATIONS SENSITIZATION AND MOBILIZATION ACTIVITIES
It is irnportant to recall that since 1974, OCPProgramme management
the need to get various community social elements involved in sensitizationand
mobilizationactivities whenever this was feasable.
As from1975 an information campaign through the media and health education services was launched
tosensitize people about the dangers relating
onposters and in the rnedia was used. The communities were rapidly able to understand the relationship between the black flies and blindness as
wellas the objectives of the programme. They understood the weekly intervention of airplanes and helicopters that carried out aerial larviciding.
didnot target populations at
risk only. Theyalso targeted
administrative and health authorities toensure
They also targeteddonors countries which were concerned
ofan action they were supporting.
Population sensitization and mobilization activities areensured
by VCU teamsduring entomological prospections, and by national teams before epidemiological evaluations and ivermectin distribution.
All the socialsegments as
the politicaland administrative authorities
in theareas visited by the teams were targeted by the sensitization (teachers, traditional healers, health agents and religious leaders, etc.).
Talks were organized and leaflets on OCP activities were distributed
inthe villages; and
filmswere shown anytime that was possible.
followingthemes were discussed during the talks
*Onchocerciasis transmission; relation between the
black fliesand the disease
clinicalsigns of the disease: itching, acute skin lesions (onchocerciasis dermatitis), nodules, chronic cutaneous symptoms (depigmentation), dimsight (progressive visual impairment, blindness).
*The socio-economic consequences; disabilities (blindness), abandonment
of firstline villages (closest to the
river)and most fertile valleys, which is an obstacle
tosocio- economic development.
*The control of the disease, vector control, ground
Regarding vector control, the involvement of the populations isrequested
to lookafter kerosene and insecticde stocks to prevent theft.
is laid on thedoses
on patients'size, contra-indications,
regularity,side effects and appropriate behavior.
The progressive intensification
ofsensitization resulted in the gradual increase in the coverage
of ivermectin distribution. It also resulted in the easieracceptance
of skin snipduring epidemiological surveys.
vector control isconcerned,
led to asignificant reduction of cases of theft of kerosene and insecticides in the depots in the field.
. Flycatching data
to2001 showed a particular pattern
variation in fly
snecies oooulation. The seasonal variation is between S. datnnosuln s.s and S. sirbanum on one hand and S. soubrense
Beffa formon the other. From the analysis
it isclearly shown that S. soubrense Beffa form becomes the major component of the
inthe Oueme basin
rainyseason and completely absent during
This is true onlyat the stronghold
ofS. soubrense Beffa
formareas (the Oueme
to Aguigadji,and on the Okpara from Kaboua to the confluence
withthe Oueme). See radar graphs on seasonal variation
S. soubrense Beffa form at Atchakpa and M'Betekoukou
of the"attack phase"
of aerial larviciding todate,
vectorcontrol operations have produced very good results, as can be seen in the various
(fig. l2and 13).
Insome places the ATP had rapidly fallen to very
less than 100 is recorded
insome places. after
inthe Oueme basin
is very rapidcompared
control. Thisrapid drop in ATPs can be attributed to three factors:
firstfactor, being the severe drought,
in1983. From the graphs
theOueme and the tributaries,
it isshown that after
thedrought, and even four years before aerial
larviciding,the ATPs had started dropping already. These ATPs
didnot come up to their
originalvalues after the end of the drought, which was marked
withthe beginning of the 1985 rainy season.
Infact. the ATPs remained low
tillthe beginning of aerial
ivermectin distribution in theOueme basin
Ithas been shown that the intake
ofivermectin by the human population
inan area can reduce the rnean microfilariae load (mf1 in the skin of treated person by 96%,
- 99%. After12 months, tl-re subsequent mf-repopulation
of its original level(Remme J. et
The reduction of microfilariae load in thehuman population therefore results
in the reduction of infectivelarvae
isbased on the presence
(L3H)in the head of the
low iffew L3Hs are obtained.
thirdfactor is vector control
itself.From the graph
can be seen that. although the basin is contaminated each year
byS. soubrense Beffa
form fliesfrom Nigeria, there is progressive downward trend. This means, there is gradual reduction
in flypopulation each year. indicating good control strategy
(fig.10 and 1 1 ).
Itis irnportant also to comment on the vectorial role of the S. soubrense Beffa form in the Oueme bassin.
As already mentioned earlier on in this report, S. soubrense Beffa form is the major transmitter
byS. soubrense Beffa
only ( fig.
in the dryseasou as
it is in thecase
of S. squamosum inperennial
al1991). On the other hand.
ithas been shown
thatS. yahense does not sliow any major seasonal variation in transmission (Cheke el
ul1992). This therefore, means that
Beffa formwere not to be a contaminant
ofthe Oueme. the
ATPs wouldhave been lower tlran what they
actuallyare. This can be seen in the parts of the basin, which are not the strongholds
S. soubrense Beffa
Ifone compares the ATPs
itcan be seen that, the values of ATPs in the strongholds are 3 to 4 times higher.
10.4. It isimportant
very little from their points of arrival in theOueme basin, namely,
the LowerOkpara and
They are therefore rarely found
or tothe north
Although ithas been shown in the laboratory that S. soubrense Beffa form can
flylong distances (Cooter 1983), they seem to restrict themselves to the strongholds in the Oueme basin
10.5.The pre-control epidemiological data showed
for theOueme basin, around the strongholds
forS. soubrense Beffa
-80%). On the other hand prevalence
for thesame areas were
quite low(1 .70%
Beffa form, are goodtransmitters
strain of theOnchocerca parasite
(DNAlab results), the transmission does not result in the blinding type of Onchocerciasis.
is worth looking into for clarification.The question
"Is theSavannah strain
ofOnchocerca parasite transmitted
Beffa form different fromother
blindingSavannah strains found elsewhere?"
The latest entornological and the epidemiological results show that the onchocerciasis situation
inthe Oueme basin is good. There is progressive regression of onchocerciasis by way of transmission by the
fly (ATPs)and the prevalence
population. Thismeans the
inuse (cornbination of vector control and ivermectin distribution) is a good one. Especially,
ifone takes into consideration the duration of vector control in the Oueme basin.
the majority of the fly population on theOueme itself.
dryseason and late rainy season the population composition changes
toS. damnosum s.s and S. sirbanum.
The data available show that S. soubrense Beffa
form isa good and important transmitter during the
rainyseason, but not a good transmitter
dryseason. This means that
ifthere was no contamination phenomenon by S. soubrense Beffa form, the onchocerciasis situation
inthe Oueme basin would have been better.
go tothe Programme
Director ofOCP and
the Chief of VectorControl
Unit (VCU) for givingus
to writethis report.
writing ofthis report
wouldnot have been possible
VCU staffin both Ouagadougou and in the
field.This is to say a big thank you to them all.
Ourspecial thanks go
to Mr. AkéFlavien,
Nikiémaand Robert Toé
writing of thisreport,
making ofthe various graphs and the maps of this report.
to MrS. N'Gadjaga and
for allthe computer installations which made
iteasier to write this report.