House Screening - Biological and Environmental Control of Disease Vectors - page 131

2010), and the same is likely to be true of house
screening. Where mosquitoes bite outdoors but
rest indoors, such as An . culicifacies in Sri Lanka
(Gunawardena et al ., 1998), house screening
should have partial success at the very least:
exposing vectors to harsh outdoors conditions
could reduce average life expectancy and thereby
reduce vectorial capacity.
It is true that not all houses will be suitable
for screening. Poorly or partially built rural
tropical houses can be missing entire walls,
while others have unusually large eave gaps or
are made of such poor quality materials that it is
likely the house will not last for the lifetime of the
screening. But no intervention tools are truly
universally applicable. All public health control
interventions must identify and address the
socio-economic factors that have the greatest
infl uence on acceptability and use. Perhaps most
critical to the acceptability of house screening
are the related issues of durability, af ordability,
ventilation and indoor microclimate.

curtains in the past, i.e. that they are dii cult to
install and keep in good condition (Greenwood,
1999). Nevertheless, several studies of curtains
have demonstrated that even without a perfect fi t
to completely exclude mosquito entry, a large
reduction in indoor mosquito densities can be
achieved and maintained (Habluetzel et al .,
1999; Fanello et al ., 2003). It seems likely that
this is also the case for house screening. If
mosquito passage through holes in screening is
in future demonstrated to be a signifi cant
problem, the protective ei cacy duration of the
screening could be extended by treating it with
insecticide. Unsurprisingly, the best approach to
maximizing durability is to use the most
appropriate screening materials. Sophisticated
porch screening systems sold in the USA (e.g.
Screen Tight TM and ScreenEze®) use heavy-duty
weatherproof UV-resistant vinyl or fibreglass,
and claim to be resistant to scratching by animals
and ideal for areas where children push against
the screening. These systems use cambered
aluminium framing to retain screen tension, and
the screening is usually held in place by a rubber
spline in the frame, allowing the material to be
easily removed, repaired and replaced without
damage to the material or the frame. If such
technology could be made cheap enough for use
in impoverished rural communities, it would
provide increased durability over the simple
traditional system of staples plus wooden trim. In
a system where panels can be removed,
alternative materials could be used seasonally
according to the most important parameter,
including stopping insects, maximizing
ventilation or even reducing heat loss. Screens
using Velcro TM already exist for this purpose in
the USA and are used in experimental hut trials
in the tropics where panels need to be oriented or
rotated relative to the prevailing winds.
A fi nal determinant of house screening
durability is the ability and motivation of users
to make repairs. In a trial in The Gambia holes in
the netting were much more common, and
easier to repair, than damage to the wooden
frames. Although trial participants in the main
did not think they could af ord to install
screening themselves, they could af ord some
repair work and there was evidence that self-
initiated repair was happening throughout the
trial (e.g. Fig. 7.3b).

7.5.1 Durability

Studies of house screening durability are limited
in number. The durability of any house
screening intervention will be determined by the
intervention design, the construction materials
employed and the behaviour of the users.
Screened doors and (to a lesser extent) windows
must be designed to withstand frequent use as
the house occupants will be interacting with
these much more frequently than a screened
ceiling. As expected, in an intervention trial in
The Gambia, screened doors suf ered much
more damage than either windows or ceilings
(Kirby et al ., 2010). The most common causes of
damage were misuse by children and inadvertent
damage caused during the passage of domestic
animals into the house. However, it is interesting
to note that there were no statistically signifi cant
relationships between any measure of damage
after 6 months or 1 year and the number of
mosquitoes caught indoors (Kirby et al ., 2010),
which hints that screening can sustain
considerable damage before the ei cacy against
mosquito house entry is af ected.
There have been similar arguments against
house screening as have been used against