Agriculture Reference
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feeding and therefore renders the insect
unable to transmit the disease. This effect
has proved unstable, however. Another
approach involves engineering insect denso-
viruses to deliver RNA copies of genes
required for vector competence in the
mosquito. Because RNAi suppresses trans-
cription of genes where double-stranded
RNA copies of that gene are present, this
approach prevents the expression of genes
required for vector competence and the
insect is again unable to transmit disease.
reduced survival when feeding on humans
shortly after drug administration (Chaccour
et al.
, 2010; Kobylinski, 2010). Bockarie
et
al.
(2002) also demonstrated similar drug
use treatment resulted in the death of
An.
punctulatus
. Kobylinski (2011) found that
mass drug administration of ivermectin to
humans in Senegal reduced the survivorship
of wild-caught
An. gambiae
sensu stricto
and probably
An. arabiensis
up to a period
of 6 days post-administration. It also
reduced the proportion of fi eld-caught
P.
falciparum
-infected
An. gambiae
s.s. for at
least 12 days post-treatment.
Sublethal doses of ivermectin can also
inhibit the sporogony (development stages)
of
P. falciparum
in the mosquito (Kobylinski
et al.
, 2012). Chaccour
et al.
(2013) proposed
that there may be a role for ivermectin to be
administered to prevent malaria trans-
mission from patients in the fi rst weeks
after treatment with Artemisinin Combin-
ation Therapy (ACT) when they would
otherwise remain infective.
HEGs
HEGs are genetic elements discovered in
bacteria and introduced into
Ae.
aegypti
and
An.
gambiae. They are an example of
'gene drive' as they are preferentially
inherited and therefore only small numbers
of insects need to be released for the trait to
spread in the population. They can be
engineered to recognize sequences in genes
known to be required for vector competence
and, once inserted, they deactivate the gene
and code for endonucleases that deactivate
the copy of this gene on the paired chromo-
some and become inserted there as well.
This converts HEG heterozygotes into
homozygotes and drives the HEG gene
through the population, destroying vector
competence in the process. Alternatively,
HEGs can be used as a form of population
suppression by deactivating genes to induce
sterility or to cause reductions in survival or
distortions in sex ratio. Simulation models
on
An. gambiae
show HEGs could eliminate
this mosquito species.
Spatial Decision Support Systems
The advent of Global Positioning System
(GPS) and Geographical Information System
(GIS) technology has enabled precise and
rapidly updated, location-based analyses of
diseases and vector incidence. Computing
capability offers the potential to build this
information into Spatial Decision Support
Systems (SDSS) that focus the interventions
for vector management onto the areas
required. Several such systems have been
developed, principally for malaria, but also
for dengue, and have been reviewed by
Kelly
et al.
(2012).
Human drug for mosquito control
Many studies have demonstrated the sus-
ceptibility of
Anopheles
to ivermectin
through blood feeding. For example, Foley
(2000) found that a single oral dose of 250
μg/kg resulted in 93% mortality of
Anopheles farauti
when feeding takes place
7 days after the drug administration and
40% mortality if feeding takes place 14 days
after administration.
An. gambiae
and
An.
arabiensis
were also tested and showed
Malaria
Martin
et al.
(2002) described the use of an
SDSS at national level in South Africa in
1998/9 for mapping malaria and highlighting
priority areas for treatment. A system
developed in Tamil Nadu, India, enabled
programme managers to identify clusters of
malaria cases and rapidly determine their
probable causes, so the most appropriate
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