Progress & ImPact serIes - Roll Back Malaria - World Health ...

Vectors: Vector behaviour contributes to the
different epidemiologies observed. There are
three highly efficient forest vector species
in Asia, namely: An. minimus, An. Dirus, and
An. Fluviatilis (21). An. dirus is a shade-loving
deep-forest species: its archetypal breeding site
is an elephant’s footprint filled with dead leaves.
It has a long lifespan and a strong preference
for primate blood (and in forest villages, human
are often the most abundant primates). Despite
sometimes being responsible for less than 5% of
bites it can still cause the majority of infections.
An. minimus is associated with the forest-fringe
and breeds in the pools formed at the edges of
mountain streams which may have emergent or
dangling vegetation. An. minimus is more common
than An. dirus but has a shorter lifespan than and
is more zoophilic. An. fluviatilis is associated with
intense malaria transmission in forested areas
of Orissa, India, and is commonly found around
slow moving streams, springs, and irrigation
channels. The species is mainly zoophilic and
only moderately long lived. An. culicifacies is
responsible for much of the transmission of
malaria in plain areas but it is not an efficient
vector. It is an endophilic mosquito with females
feeding outdoors and often resting indoors.
Because it rests on the walls of houses it is easily
controlled by IRS. Larvae of An. stephensi are
commonly found in man-made structures such
as water tanks, roof gutters, and collections of
water on building sites in urban areas.
Interventions: Development activities have had
an important influence on malaria transmission
over the years (21). In Kheda District, India,
marshy land that sustained large populations of
An. culicifacies was reclaimed for rice cultivation
in the 1980s which led to a reduction in malaria
transmission. In Indonesia, prawn and fish
culture requiring high salinity proved injurious
to An. sundiacus, thus eliminating its breeding
in the coastal areas affected. Widespread
deforestation in Asia has destroyed the habitats
of some of the most efficient malaria vectors
although in some cases natural forests may be
replaced by oil palm plantations which are also
associated with a high malaria risk (24).
Preventive measures have also contributed to
malaria control. More than 150 million people in
the region were protected with IRS in 2009; IRS
covers more than 5% of the population at highest
risk in Bhutan, Democratic People’s Republic
of Korea, India, Malaysia, Nepal, and Sri Lanka.
Larvivorous fish are used in India, Indonesia,
Myanmar, Sri Lanka, and Thailand. The number
of ITNs distributed by national malaria control
programmes between 2007 and 2009 was
sufficient to protect approximately 70 million
people with coverage potentially exceeding
10% in Cambodia, the Lao People’s Democratic
Republic, Malaysia, Sri Lanka, and Timor-Leste
but in no case exceeding 20%. The apparent
low coverage of preventive measures may be
due to populations at risk being overestimated;
when transmission is very focal the risk of
transmission may be confined to only a small
percentage of the population and preventive
measures need to be targeted to ensure efficient
use of resources (Box 3.2). It is also evident
that populations acquire mosquito nets from
sources other than national malaria control
programmes and so are not accounted for in
quantification exercises. These nets tend not to
be treated with insecticide. Household surveys
suggest that 80% of children under five years
of age sleep under a mosquito net in Cambodia,
the Lao People’s Democratic Republic, and
Viet Nam, but only a small percentage of these
were treated with insecticide (ITNs) (25). Hence
the national malaria control programmes have
emphasized treating existing mosquito nets as
well as distributing new ITNs in order to boost
the proportion of the population that have access
to them. This strategy differs from that practiced
in most other regions of the world in which
retreatment of nets has been discontinued owing
to the introduction of long-lasting insecticidal
nets (LLINs) which do not need retreatment.
DEFEATING MALARIA IN ASIA, THE PACIFIC, AMERICAS, MIDDLE EAST AND EuROPE
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