Asidi, N.

Karch, Saïd

Manzambi, Z.

Mouchet, Jean

Salaun, J. J.

Horizon / Pleins textes

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Journal of the American Mosquito Control Association, 1 l(2): 19 1-194, 1995 
Copyright O 1995 by the American Mosquito Control Association, Inc. 
IMPACT OF DELTAMETHRIN-IMPREGNATED BEDNETS ON 
I BITING RATES OF MOSQUITOES IN ZAIRE 
b 
S .  KARCH,' N. ASIDIY2 Z. MANZAMBIY2 
J. J. SALAUN3 AND J. MOUCHET3 .. 
ABSTRACT: In a rural area of Zaire, the whole population of a village was protected by deltamethrin- 
impregnated m$squitoes bednets. A similar village was observed as a control. Biting rates for mosquitoes 
were recorded in both villages. The principal man-biting species were Mansonia africana, Mansonia 
uniformis, and Aedes aegypti. In the village protected by the impregnated mosquito bednets, t.hG,number 
of Mansonia bites was reduced 96% indoors and at a lesser rate outdoors. Biting rates of Ae. aegypti 
dropped to O indoors, but the outdoor biting rate remained unchanged. It is concluded that the reduction 
in mosquito bites is not only caused by the repellent action of the deltamethrin but also by a reduction 
in mosquito numbers. 
INTRODUCTION 
The use of insecticide-treated mosquito bed- 
nets for the control of malaria has generated much 
interest (Bermejo and Veeken 1992). Insecticide- 
impregnated bednets have been used successfully 
in several countries: China (Li Zuzi et al. 1989), 
Gambia (Lindsay and Adiamah 1992, Alonso et 
al. 1993) and Burkina Faso (Robert and Came- 
vale 199 l), In a study in Zaire, this strategy re- 
sulted in a reduction in the number of bites from 
the malaria vector Anopheles gambiae S.I. by 94% 
(Karch et al. 1993). Parasite inoculation rates in 
the treated area were similarly reduced. Addi- 
tionally, other pests such as bedbugs, ticks, and 
lice were controlled by the treatment (Lindsay et 
al. 1989). 
In this paper we evaluate the effect of delta- 
methrin-impregnated mosquito bednets on the 
biting rates of the significant species Mansonia 
africana (Theobald), Mansonia uniformis (Theo- 
bald), and Aedes aegypti (Linn.) 
whom share the same bed, particularly children 
and their mothers. Distribution of bednets was 
based on the number of beds in the village. Some 
800 mosquito bednets impregnated with delta- 
methrin (K-Othrinm) at the rate of 25 mg/m2 
were issued. The number of houses in the village 
was 450. 
The village of MbansalC, with some 900 in- 
habitants and 135 houses, served as a control. It 
should be noted that the residents ofboth villages 
were protected against malaria attacks by the use 
of chloroquine and quinine made available at 
local health centers. 
From February 1990 to November 1991, 
weekly collections were made in each village by 
a team of 6 collectors and a leader. The teams 
worked from 1700 to 0600 h, with 3 collectors 
in the same room as the treated mosquito bednet 
and 3 outside the house. The most abundant 
species were Ma. africana, Ma. uniformis, and 
Ae. aegypti. The daily biting of Mansonia species 
was calculated for the 1700-0600 h time period, 
whereas the Aedes rate was estimated from 1700 
to 2 1 O0 h because its activity fell off at 2 1 O0 h. MATERIALS AND METHODS 
The 2 villages selected for this study were sit- 
uated some 60 km east of Kinshasa on the Bateké 
plateau in Zaire. The distance between the 2 vil- 
lages was 8 km. Houses in the 2 villages are 
clustered in widely dispersed compounds. Most 
houses consist of 2 rooms and have mud and 
stick walls. Approximately 50% of the houses 
have corrugated tin roofs. 
During the first year (February 1990-January 
199 I), entomological baseline data were collect- 
ed. Subsequently the village of Mbangu-mbamu 
was selected as the trial site for control of malaria 
using impregnated mosquito bednets. Mbangu- 
mbamu has some 3,000 inhabitants, many of 
Department of Medical Entomology, 72 Route 
INRP, B. P. 1 197, Kinshasa, Zaire. 
d'Aulnay, 93 140 Bondy, France. 
3 ORSTOM, 2 13 Rue Lafayette, Paris, France. 
Distance from breeding sites to the village was 
200 m for Mbangu-mbamu and 100 m for Mban- 
salé. 
RESULTS 
The effect of the mosquito bednet treatment 
on the 2 Mansonia species was similar. The bit- 
ing rate for Ma. africana decreased from 11.5 
per night to 0.4 in the room with the mosquito 
net, a reduction of 96.5%. Differences between 
the treated area and the control were significant 
(x2 = 5.73, P = 0.01). No significant differences 
were noted for the outdoor biting rate oc2 = 1.33). 
In the control village, both indoor and outdoor 
rates remained unchanged and similar to that of 
the pretreatment years (Fig. 1). 
The indoor biting rate for Ma. uniformis de- 
creased by 92% k2 = 3.71, P = 0.05). No sig- 
191 
I A h  vsa..w Document.aii.6 
192 JOURNAL OF THE AMERICAN MOSQUITO CONTROL ASSOCIATION I VOL. 1 1, NO: 2 
Mansonia africana 
_c Outdoor control -t- Outdoor treated 
-C- Indoor control -e-- Indoor treated 
60 - 
40 - 
20 - 
nificant differences were noted for the outdoor 
biting rate (xz = 2.27) in the protected area, and 
biting rates remained unchanged in the control 
(Fig. 2). 
The indoor biting rate of Ae. aegypti was O 
(Fig. 3), but it should be pointed out that the 
biting rate was never very high. The outdoor 
biting rate remained unchanged. In the control 
area, the situation remained the same during the 
2 years. 
60 
40 
20 I 
o '  0 
1990 Pre-treatment 4 Impregnated nets 1991 
I I  I I ' I ' '  ' 
J F M A M J J A S O N D J F M A M J J A S O N D  
Mansonia uniformis 
Outdoor control + Outdoor treated - 
+ Indoor control -ff- Indoor treated 
Fig. 2. Biting of Mansonia uniformis in 2 villages before and after treatment with impregnated bednets. 
4 i. JUNE 1995 DELTAMETHRIN-IMPREGNATED BEDNETS 193 
b 10 
O 
.r 
10 
8 
6 
4 
2 
O 
J F M A M J J A S O N D J F M A M J J A S O N D  
1990 Pre-treatment 4 Impregnated nets 1991 
Aedes aegypti 
Outdoor control + Outdoor treated - 
I I +t+ Indoor control -e- Indoor treated 
Fig. 3. Biting of Aedes aegypti in 2 villages before and after treatment with impregnated bednets. 
DISCUSSION 
Mosquitoes are a serious problem on the Ba- 
tek6 plateau. The average culicine biting rate is 
91 per night, compared to 26 for anophelines. 
Under such conditions, the acceptance of treated 
mosquito bednets is important because it is an 
effective method of control. Both Ma. africana 
and Ma. uniformis are considered to be major 
pest species (Karch et al. 1992). 
The reduction of Mansonia species inside 
houses was welcomed by the population as the 
bites of these mosquitoes are painful. This re- 
duction could be caused by the repellent action 
of deltamethrin or a decrease in the numbers of 
mosquitoes. The decrease in outdoor biting rates 
supports the latter hypothesis. Such insect pop- 
ulation reductions following ithe use of impreg- 
nated mosquito bednets by an entire community 
has been observed in China with Anopheles si- 
nensis Wied. and Anopheles anthropophagus Xu 
& Feng (Li Zuzi et al. 1989). This effect was not 
anticipated for Mansonia, which are primarily 
outdoor biters. 
The reduction to a O biting rate for Ae. aegypti 
is interesting, but we make no conclusions be- 
cause the biting rate was already low. Further 
investigations in areas of high Ae. aegypti pop- 
ulation densities should be carried out to deter- 
mine the precise effect of deltamethrin. Outdoor 
biting rates of Ae. aegypti remained unchanged. 
This finding would support the hypothesis of a 
genetic segregation between the indoor and out- 
door populations of Ae. aegypti observed in East 
Africa (Trpis et al. 1973). 
ACKNOWLEDGMENT 
We thank Pierre Carnevale, TDR-WHO/OMS, 
Geneva, Switzerland, for his support and sug- 
gestions. 
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c 
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Impact of deltamethrin-impregnated bednets on biting rates of mosquitoes in Zaire

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