The efficacy of using new
strategies for malaria vector control was studied in certain insecticide-
resistant areas in Africa in an attempt to reduce malaria prevalence and to
bring about better management of the disease.
A lot of effort and
international funding is being directed towards the control and elimination of
malaria. Nevertheless the disease remains an issue of major public health
concern, as the efforts to control and eliminate malaria in Africa are
being challenged by the development of resistance by the parasites to
It has been estimated
globally that there are nearly 216 million cases of malaria per year with about
655 000 deaths, 86% of whom are children below the age of 5 years.
The World Health
Organization (WHO Global Malaria Programme-Roll Back Malaria [RBM] Partnership)
has issued a few recommendations to fight malaria. Their methods include
artemisinin-based combination therapy, long-lasting insecticidal nets (LLIN),
indoor residual spraying of insecticide (IRS) besides intermittent preventive
treatment during the pregnancy period. A combination of insecticide is employed
in the combined use of IRS and LLIN. This has not only helped to check malaria
effectively but is also capable of delaying the emergence of insecticide
-resistant strains of the vector.
In just two years, between
2008 and 2010, approximately 289 million insecticide-treated mosquito nets were
distributed in sub-Saharan Africa; this number was enough to protect 578
million people. Additionally, nearly 81 million people, representing 11% of the
population at risk, were also protected by IRS.
It was observed that such
management strategies brought about a reduction in the incidence of malaria in
areas with moderate to high prevalence in the sub Saharan regions. However of
late a spurt in the incidence was observed in some African countries and this
points a finger at the fragility of the malaria- control programs employed in
these high risk zones.
The main goal of malaria
vector control is to bring down the vector capacity of local mosquito
populations below the critical threshold number required to achieve a malaria
reproduction number below one. Unfortunately, the present control methods
employed, (LLIN and IRS) are extremely dependent on just a single class of
The malaria vectors have
developed various resistance mechanisms anti- pyrethroid resistance mechanisms,
hence there was a need to generate new strategies that would check the growth
of pyrethroid-resistant malaria and prevent disease transmission in high-risk endemic
The present study aims to
find out if the use of both LLIN plus IRS or LLIN plus carbamate-treated
plastic sheeting [CTPS] offered better control of malaria and decreased
pyrethroid-resistance in malaria vectors compared to a selective usage of LLIN,
in children younger than six years. It also aims to find out if the universal
coverage of LLIN could afford better protection against malaria by exerting a
mass killing effect than would selective coverage.
A randomised controlled
trial was carried out in 28 villages in southern Benin, west Africa between
June 23 2008, and Dec 24 2009.Inclusion criteria of the villages was that they
needed to be within a distance of 2km between each other, have moderate levels
of pyrethroid resistance in malaria vectors and an absence of health care
centre. Of 58 villages included in the study,28 were randomly assigned to
vector control intervention -TLLIN, ULLIN, TLLIN+IRS, and ULLIN+CTPS.
Inclusion criteria for
children were age between 0-71 months and domicilliation in these villages. A
random sample of children was obtained from each village. Follow up was done on
413-429 children in each intervention group for 18 months. They were of the
same age group and sex ratios.
Study investigators and
children were not masked to treatment allocation.
Active checking for
malaria episodes was done on children during 12 periods of 6 consecutive days
at six weekly intervals. A nurse collected data and blood from sick children
and everything was supervised by a doctor. Children were treated depending upon
the clinical diagnosis made.
During the period from Jan
14, to Dec 24, 2009, mosquitoes were collected every 6 weeks through eight
surveys of 2 consecutive days and examined for morphology and parity rates.
Heads and thoraces of anopheline female mosquitoes were tested to detect Plasmodium
circumsporozoite protein (CSP) through the ELISA test.
An attempt was made to see if new
strategies would help control malarial incidence in endemic, pyrethroid
-resistance areas. The study revealed
that there was no added benefit in using a combination of vector control
The trend was the same with regard to the parasite density
and prevalence of asymptomatic infections. The insecticide combinations could
not stop the evolution of kdr allele in Anopheles gambiae s.s in comparison to
The rapid evolution of the
allele which contributed to
resistance in malaria vectors, the short-term activity of the carbamate used in
IRS treatment, and the overall behavioral transformation in the vector
populations in response to the various treatments are all causative factors
that contributed to the lack of treatment effect.
There are several other
factors too that have influenced the outcomes, including access to diagnosis
and treatment and the effective use of vector control intervention.
The above results could be
an obstacle to the ongoing malaria elimination programs in Africa.
"Combination of malaria
vector control interventions in pyrethroid resistance area in Benin: a cluster
randomised controlled trial"; Dr.Vincet Corbel et al; The Lancet Infectious