Sanitation and Vector Control - Biological and Environmental Control of Disease Vectors - page 147

The study in The Gambia also investigated
the impact of spraying with insecticide on the
number of M . sorbens fl ies, associated with
trachoma infections, and found a consistent
75% reduction in fl y populations over both wet
and dry seasons, an overall 61% reduction in
active trachoma cases and a 75% reduction in
the risk of becoming a new trachoma case
(Emerson et al ., 1999). However, in Tanzania,
there was no additional ef ect of weekly space
spraying using 10% permethrin on trachoma in
periods following mass treatment with
antibiotics (West et al ., 2006). The introduction
of fl y screens in broiler houses on chicken
farms has been found to have an impact on
Campylobacter spp. The installation of fl y screens
in 20 broiler houses during the summer of
2006 in Denmark prevented the infl ux of fl ies
and caused a decrease in Campylobacter spp.-
positive chicken fl ocks from 51.4% in control
houses to 15.4% in intervention houses (Hald et
al ., 2007).
Based on past evidence, fl y control could
result in an approximate 25% reduction in
diarrhoeal disease and a 75% reduction in
trachoma cases, but it has not often been
included in public health programmes, pre-
dominantly as a result of the high material and
labour cost of insecticide spraying. No environ-
mental fl y control strategy has yet been shown
to be sui ciently cost-ef ective, though spraying
during epidemics may prove to be so (Chavasse
et al ., 1999).

the ability of vectors to transmit sanitation-
related diseases.
A wide range of sanitation technologies
exists to keep human excreta separate from
humans, thereby reducing the potential trans-
mission of pathogens. These may be divided into
open defecation, on-site sanitation and of -site
sanitation systems. The most common forms of
on- and of -site sanitation will be discussed
below.

8.3.1 Open defecation

In rural and urban areas, where open defecation
is practised, public defecation sites are well
defi ned areas at the edge of a community or
village. In many cases, public or communal
lands, such as river banks, land adjacent to
railway tracks, roads and agricultural fi elds are
designated for open defecation. At these sites,
excreta are normally not covered, and thus
exposed to the elements to break down and
decompose. In contrast, the extensive use of
plastic bags in urban or semi-urban areas for
defecation purposes makes normally well
demarcated public defecation sites less
pronounced, thereby possibly increasing the risk
of fl y-borne contamination of foods.
Open defecation sites are normally dry,
because people do not like to wade through
water to defecate. Therefore, they are not usually
associated with mosquito breeding unless the
open defecation site becomes marshy due to
heavy rainfall. In these instances, mosquito
breeding is more associated with the absence of
good water management practices than it is with
sanitation. The large number of fl ies at public
defecation sites is often mentioned, together
with the presence of prickly bushes, snakes and
other vermin, as a drawback of open defecation
(Jenkins and Curtis, 2005).
There is a wealth of evidence that M .
sorbens , the vector of trachoma, selectively
breeds in exposed and scattered faeces lying on
the ground (Emerson et al ., 2001). There seems
to be a strong preference for human faeces, but
fl y maggots have also been retrieved from
scattered faeces from dogs, cats, horses, pigs,
donkeys and cows (Emerson et al ., 2001).
Trachoma is common in underprivileged
communities in sub-Saharan Africa, Asia, South

8.3 Sanitation Technology, Vector
Breeding and Control

Flies, cockroaches and mosquitoes all thrive in
the absence of basic, or poorly functioning,
sanitation as it provides them with a stable
supply of food and breeding sites. However, the
impact of poor sanitation dif ers for each
infectious disease and vector. In addition, the
presence of large numbers of fl ies, cockroaches
and mosquitoes in latrines, drains and septic
tanks might deter people from using,
maintaining and cleaning sanitation facilities
(Jenkins and Curtis, 2005) . This section will
focus on the impact of both the absence of
sanitation, and dif erent sanitation technologies
and their management, on vector breeding and