House Screening - Biological and Environmental Control of Disease Vectors - page 127

It is relatively common to fi nd ceilings in
urban houses in the tropics. A study of house
proofi ng methods in Dar es Salaam found almost
half of the houses sampled had ceilings, 88% of
which were made from plywood boards and 5%
from mud or palm leaves (Ogoma et al ., 2009).
The motivation for installing ceilings was
primarily to restrict mosquito house entry, but
also to keep the house cool and to make the
interior more beautiful (Ogoma et al ., 2009).
Similarly, in a peri-urban coastal settlement in
The Gambia, 75% of surveyed houses had
ceilings in bedrooms, if not the whole house
(Lindsay et al ., 1990). These ceilings, simple
corrugated cardboard sheets tacked on to a
wooden frame, of ered protection against An .
gambiae s.l. house entry; 32% of rooms without
ceilings contained malaria vectors versus only
14% in rooms with ceilings (Lindsay et al .,
1990).
Descriptive and risk factor studies have
shown that ceilings are associated with a 13-
56% reduction in indoor An . gambiae s.l.
densities (Lindsay et al ., 1990, 1995; Adiamah
et al ., 1993), and experimental hut evaluations
provide supporting evidence. A range of ceiling
treatments tested in experimental huts in The
Gambia, including plywood, synthetic netting
and plastic insect-screen material, all sig-
nifi cantly reduced the number of indoor vectors
( An . gambiae s.l. and Mansonia spp.) compared to
a no-ceiling control (Lindsay et al ., 2003). That
these treatments were ef ective even when doors
and windows were left ajar, and without
insecticide, is indicative of the value of
mechanical prophylaxis against species that
favour eave entry into houses. In addition it is
important to note that the mesh treatments did
not raise the indoor temperature compared to
the control, and were signifi cantly more ef ective
than the plywood ceiling (70-80% reduction in
mosquito numbers versus 52-59% reduction).
This suggests that mesh ceilings, which allow air
carrying host odours to permeate the holes, can
attract and trap mosquitoes in the roof space. In
a randomized-controlled intervention trial, also
carried out in The Gambia, installing PVC-
coated fi breglass mesh ceilings signifi cantly
reduced house entry by An . gambiae s.l. (ratio of
means 0.53), entomological inoculation rates,
and anaemia in children (adjusted OR 0.51)
compared to unscreened houses (Kirby et al .,

2009). However, Culex spp. densities were much
less reduced by the ceilings.
Ceilings could also have a role in reducing
Chagas disease. Despite the proven connection
between palm roofs and triatomine bug house
infestation, this type of roof is still common in
South and Central America. In 2003 over 60%
of roofs in villages within Barinas State,
Venezuela were at least partly covered by palm
thatch and over 40% made exclusively of this
material (Sanchez-Martin et al ., 2006). Replac-
ing thatch roofs with corrugated metal is of
course the best solution, but for many this is
unaf ordable. In these situations a simple ceiling
that operates as a physical barrier to separate
the roof space from the living space below could
help reduce human-vector contact.

7.4.3 Door and window treatments

Screened doors and windows must fi t tightly into
the apertures, be sturdy enough to resist regular
opening and closing, and be secure against
thieves. It may be necessary to reconstruct or
reinforce the doorway or window aperture before
frames are fi tted. The screening material should
be permanently fi xed to the frame and reinforced
at the corners and edges, where it might
otherwise tear or come away from the frame.
Handles and push bars should be positioned at
suitable heights to allow both children and adults
to open the doors or windows without needing to
push directly on the screening. Simple catches on
the inside would allow doors and windows to be
secured from the inside at night. Finally, elastic
cords or coil springs should be attached to the
inside of doors so that they will close
automatically. Ideally, screened panels should be
fi tted innermost of existing doors and windows.
This would allow the residents to close the
screened panels, but leave the external fi xtures
open on hot nights to permit the passage of air
but not insects. Mosquito-proofi ng walls requires
the repair of cracks and holes in addition to
screening doors and windows. It is a fairly
common practice in Tanzania, Zambia (personal
observation) and probably elsewhere in Africa, to
deliberately leave or create small holes in mud-
and brick-walled houses for illumination and/or
ventilation, and these are often an alternative to
windows. These small holes should also be