Biology Reference
In-Depth Information
screening is becoming increasingly available in
rural towns of tropical and subtropical
countries. Fibreglass screening, woven from
strong glass yarn and coated with protective
vinyl (usually PVC), is the best available
material for house screening. It is resistant to
rot, fi re, corrosion, shrinking and staining and
available in many colours and weaves. Vinyl-
coated polyester is an alternative that is stronger
than fi breglass and could be used for lower
panels of doors with standard fi breglass
screening in upper panels. Dual purpose
screening has been developed to reduce solar
heat gain indoors while maintaining maximum
insect protection, e.g. Suntex® and Sunscreen®
(Phifer Inc.). Any material that can absorb and
dissipate a large percentage of solar heat and
glare while protecting against vector entry will
be ideal for tropical settings. Further advances
in screening technology, including structurally
insecticidal fabrics (currently being developed
by the Institute for Materials Research at the
University of Leeds, UK) and one-way entry
netting (Mikko Aalto, personal communication)
that would trap insects on contact or allow
exiting whilst preventing entry, should improve
the ei cacy of house screening.
Perhaps the ideal screening approach is a
combination of all the eave-, ceiling-, windows-,
doors- and curtain-treatments discussed,
providing that it does not reduce ventilation
and/or increase indoor temperatures to such an
extent that human comfort is compromised.
Combinations of treatments are already being
observed in the tropics. For instance, in 579
houses surveyed in Dar es Salaam, 57% had two
of three methods (eaves/ceiling/window
screening) and 9% had all three (Ogoma et al .,
2009). The general belief of those householders
was that complete proofi ng would provide
greater benefi t than any one of these methods
on its own. In The Gambia, screened ceilings
alone were as ef ective as full screening in most
outcome criteria, but the latter provided greater
protection against culicine mosquito house
entry (Kirby et al ., 2009) and, again, was more
acceptable to the study participants for a range
of social reasons (Kirby et al ., 2010). Ultimately
it will be socio-economic considerations that
dictate which screening approach is most
adopted.
7.5 Socio-economic Considerations
Until recently, the perception of house screening
by the scientifi c community has been that, in
principle, it might reduce house entry by vector
species, especially endophilic and endophagic
mosquitoes, but that disadvantages would be too
numerous for it to be a practical solution for
vector control. The degree of protection af orded
against vector-borne diseases would be slight, it
would be very dii cult to install screening on a
large scale, it would be costly, it would not be
durable, it would make the indoor environment
too uncomfortable for the occupants, and in
combination, these factors would make house
screening unacceptable to rural tropical
communities. One very common criticism is that
house design shows considerable ethno-
geographic variation and, as such, the screening
must be tailor-made to suit individual houses.
However, these types of criticism could also be
levelled at other vector control tools; even the
simple bed net. The individual preferences of
insecticide-treated net users have had such an
infl uence on manufacturers that companies
such as Vestergaard Frandsen and Sumitomo
now produce nets in at least three dif erent
shapes, ten colours, fi ve sizes and a range of
fabrics and deniers. Yet even with these options,
uptake is not universal - sleeping under a net
can be hot and stuf y (Alaii et al ., 2003), nets are
often used for only part of the year (unlike
screening) (Binka and Adongo, 1997; Okrah et
al ., 2002), and some houses are so small that
hanging a net inside can be dii cult (Ilboudo-
Sanogo et al ., 2001).
House screening will not work to the same
degree against all vectors. There are species with
high vectorial capacity for malaria that are
predominantly exophagic and exophilic, e.g. An .
nuneztovari in western Venezuela (Rubio-Palis
and Curtis, 1992), An . albimanus across much of
its range (PAHO, 1996) and An . gambiae s.s. on
São Tomé (Charlwood et al ., 2003). It seems
inherent that malaria transmission by such
species would not be controlled by house
screening. However, ITNs can still be ef ective in
such situations (Richards et al ., 1993;
Charlwood et al ., 2005) if peak biting is confi ned
to times when most people are indoors and
community coverage is high (Govella et al .,
 
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