Application from RBM to include insecticide treated mosquito nets for prevention of malaria
EVIDENCE OF THE IMPACT OF INSECTICIDE TREATED MOSQUITO NETS
Introduction
1
Malaria is an important cause of illness and death in many parts of the world, especially
in Africa, south of the Sahara. There has been a renewed emphasis on preventive measures, both
at community and at individual level. Insecticide treated mosquito nets are a promising
preventive measure.
2
To evaluate the potential of ITNs, efficacy trials were carried out in countries with a wide
range of transmission intensities in Africa, Asia, Latin America and the Western Pacific. The
majority of these trials were randomised-controlled trials, comparing ITN use with no net use
and, less commonly, comparing ITN use with use of untreated nets. The impacts measured have
included all-cause child mortality (age 1-59 months), incidence of severe malaria, incidence of
uncomplicated malaria episodes, prevalence of parasitaemia, mean haemoglobin level,
splenomegaly, and nutritional status.
Impact on Childhood Mortality and Morbidity
3
A Cochrane review 1 concluded that ITNs reduce overall mortality by about 20% in
Africa (range 14%-29% 2 3 4 5) and that, for every 1,000 children aged 1-59 months protected by
ITNs, about six lives are saved each year. The review also concluded that ITNs reduce clinical
episodes of uncomplicated malaria caused by Plasmodium falciparum and Plasmodium vivax
infections by 50%, as well as reducing parasitaemia. The impact on anaemia status, measured as
increases in Packed Cell Volume (PCV), is variable.
4
Having established the efficacy of ITNs under trial conditions, effectiveness trials were
conducted to evaluate impact under programme conditions. Measuring effectiveness is more
difficult and methods used have included population–based active surveillance, health service
based passive surveillance, repeated cross-sectional surveys, and case control studies. Although
the results have been varied (see Table 1), due in part to different methodologies and choices of
control groups, these trials have provided good evidence of the effectiveness of ITNs.
Table 1
Country
The Gambia
The Gambia
Pakistan
Impact of ITNs on overall mortality, mild malaria disease, parasitaemia and
anaemia, measured under programme conditions
Impact (protective efficiency 6)
Study
Longitudinal
surveillance
Case control
study
Case control
study
Overall
mortality
25-40%
0%
Mild disease
59% 8
0% 9
78% 11
69% 12
Parasitaemia
Source
Anaemia
D’Alessandro
et al (1995) 7
D’Alessandro
et al (1997)10
Rowland et al
(1997) 13
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Application from RBM to include insecticide treated mosquito nets for prevention of malaria
Tanzania
Tanzania
Cross
sectional
survey
Case control
study
62%
27% 15
63%
Abdulla et al
(2001) 14
Armstrong
Schellenburg
et al (2001) 16
5
A study in Tanzania (KINET) showed that the prevalence of anaemia in the study
population of children aged under 2 years decrea+sed from 49% to 26% in the two years studied,
and an increase in the mean haemoglobin level from 80 g/l to 89 g/l. ITNs had a protective
efficacy of 62% (95% confidence interval 38% to 77%) on the prevalence of parasitaemia and of
63% (27% to 82%) on anaemia.
Impact of the Use of Insecticide Treated Bednets in Pregnancy
6
Two of the studies carried out in Africa, south of the Sahara show that insecticide treated
bednets reduce morbidity and mortality in pregnant women. The Gambia study, carried out in a
area of high malaria endemicity with seasonal transmission and parasite inoculation rate of 1-10
demonstrated that during the rainy season there were significantly fewer primigravidae with
parasitaemia in villages with insecticide treated bednets than in control villages even though
there was no difference in the prevalence of severe anaemia or in the mean haemoglobin level.
Thus insecticide treated bednet had an effect on malaria prevalence but not on severe anaemia
which was demonstrated to be low during the dry season in women using insecticide bednets
than in control villages but no difference between the two villages during the rainy season. On
the other hand, during the rainy season there were fewer preterm deliveries among women who
used insecticide treated nets than women who used no nets. The mean birth weight of children
born in villages with treated bednets was 130g higher than that of children born in control
villages and at the individual level.
7
In an area of perennial malaria transmission in Kenya, where women receive as many as
45 - 230 infective bites on the average during 40 weeks gestation, insecticide treated bednets
were associated, in the first four pregnancies, with significant reduction a) in parasitaemia during
pregnancy (by 38%), b) at the time of delivery (by 23 %), c) in the risk of low birth weight (by
28%), and c) in any adverse birth outcome (by 25%). This impact goes beyond primigravidae to
include women of other higher pregnancy order up to the fourth. However unlike The Gambia
study, the effect was observed throughout the year, with little seasonal variation.
8
Ter Kuile et al (1999) reported that women in their first to third pregnancies living in
insecticide treated bednet villages were significantly less likely a) to develop malaria
parasitaemia compared to those living in control villages, and b) to become anaemic. The
incidence of low birth weight and low birth weight combined with stillbirths, abortions and intrauterine growth retardation were significantly reduced by 28% and 25% respectively in parities
1- 4.
2
Application from RBM to include insecticide treated mosquito nets for prevention of malaria
9
In the Thai-Burmese border (Dolan et al, 1993), with low transmission and inoculation
rate of 0.5 - 1 also showed a reduction in maternal malaria associated anaemia with insecticide
treated bednet use.
Conclusion
10
Insecticide-treated nets are effective in reducing a) childhood mortality and morbidity,
and b) morbidity and mortality in pregnant women from malaria. Increased access to insecticide
treated nets will require major financial, technical and operational inputs.
REFERENCES
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2 Habluetzel A, Diallo D, Esposito F, Lamizana L, Pagnoni F, Lengeler C, Traore C, Cousens S. Do insecticideimpregnated curtains reduce all-cause child mortality in Burkina Faso? Tropical Medicine and International Health
1997; 2(9): 855-62.
3 Binka F, Kubaje A, Adjuik M, Williams L, Lengeler C, Maude G, Armah G, Kajihara B, Adiamah J, Smith P. Impact
of permethrin impregnated bednets on child mortality in Kassena-Nankana district, Ghana: a randomised controlled
trial. Tropical Medicine and International Health 1996; 1(2): 147-54.
4
D’Alessandro U, Olaleye B, McGuire W, Langerock P, Bennett S, Aikins M, Thomson M, Cham M, Cham B,
Greenwood B. Mortality and morbidity from malaria in Gambian children after introduction of an impregnated bednet
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5 Nevill C, Some E, Mung’ala V, Mutemi W, New L, Marsh K, Lengeler C, Snow R. Insecticide-treated bednets
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International Health 1996; 1(2): 139-46.
6 Impact under operational conditions
7 D’Alessandro U, Olaleye B, McGuire W, Langerock P, Bennett S, Aikins M, Thomson M, Cham M, Cham B,
Greenwood B. Mortality and morbidity from malaria in Gambian children after introduction of an impregnated bednet
programme. Lancet 1995; 345: 479-83.
8 Matched with health centre controls.
9 Matched with village controls.
10 D’Alessandro U, Olaleye B, Langerock P, Bennett S, Cham K, Cham B, Greenwood B. The Gambian National
Impregnated Bed Net Programme: evaluation of effectiveness by means of case-control studies. Transactions of the
Royal Society of Tropical Medicine and Hygiene 1997; 91: 638-642.
11 Plasmodium falciparum
12 Plasmodium vivax
13 Rowland M, Hewitt S, Durrani N, Saleh P, Bouma M, Sondorp E. Sustainability of pyrethroid-impregnated bednets
for malaria control in Afghan communities. Bulletin of the World Health Organisation 1997; 75(1): 23-9.
14 Abdulla S, Armstrong-Schellenberg J, Nathan R, Mukasa O, Marchant T, Smith T, Tanner M, Lengeler C. Impact
on malaria morbidity of a programme supplying insecticide treated nets in children aged under 2 years in Tanzania:
community cross sectional study. British Medical Journal 2001; 322: 270-273.
15 Reduction in post-neonatal child death. Combined with coverage data this suggests that ITNs prevented 1 in 20
post-neonatal child deaths, if the effect of untreated nets is taken into account, then this increases to 1 in 10 postneonatal child deaths prevented.
16 Armstrong Schellenberg J, Abdulla S, Nathan R, Mukasa O, Marchant T, Kikumbih N, Mushi A, Minja H, Mshinda
H, Tanner M, Lengeler C. Effect of large-scale social marketing of insecticide-treated nets on child survival in rural
Tanzania. Lancet 2001; 357 (21) 1241-1247.
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Application from RBM to include insecticide treated mosquito nets for prevention of malaria
D`Alessandro U, Langerrock P; Bebbtt S; Francis N; Cham K and Greenwood BM (1996) The impact of a national
impregnated bed net programme on the outcome of pregnancy in primigravidae in The Gambia Trans Roy Soc. Trop.
Med. And Hyg. ,90,487-492.
Ter Kuile FO, Terlouw DJ, Phillips- Hopward PA, Hawley WA, Friedman JF, Kariuki S, Ya Ping Shi, Oloo AJ, Nahlen
BJ, 1999. Permethrin- treated bed nets reduce malaria in pregnancy in an area of intense perennial malaria
transmission in western Kenya. Abstracts of the 48th Annual Meeting of the American Society of Tropical Medicine
and Hygiene; Nov 28- Dec 2 1999, Abstract 11
Dolan, G ter Kuile FO, Jacoutot V, White NJ , Luxemburger C, Malankirii,L Chongsuphajaisiddhi T and Nosten 1993
Bed nets for the prevention of malaria and anemia in pregnancy Trans of Royal Soc Trop Med and Hyg 87 620-626
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