Sanitation and Vector Control - Biological and Environmental Control of Disease Vectors - page 150

Pit latrines are rarely uniformly con-
structed; Fig. 8.3 shows the diversity in pit
latrine design within one small rural community
in Tanzania. Design, choice of material, together
with environmental conditions and use and
management of a latrine are important factors
determining the attractiveness of a latrine for
vector breeding.
Although little information is available on
pit latrine construction and vector breeding, we
can assume that construction features that
attract mosquitoes to houses will also apply to
latrine construction. As outlined previously (see
Kirby, Chapter 7, this volume), there are many
features of house construction that af ect the
number of mosquito entering and resting in
houses. For example, open eaves, low ceilings,
thatched roofs and the absence of a door have all
been associated with increased numbers of
culicine and anopheline mosquitoes (Lindsay et
al ., 2003). Raised houses have been linked with
lower mosquitoes numbers (Rozendaal, 1997;
Charlwood et al ., 2003), though this is unlikely
to be a design option for a pit latrine. The design
of a latrine is in most cases a function of cost,
ease to construct, comfort and privacy. Latrines
are therefore unlikely to be constructed of brick,
concrete or metal roofs if the main dwelling is
not constructed of these materials. Although
latrine ownership and type of construction can
be seen as symbols of status (Jenkins and Curtis,
2005), in most cases latrines are constructed
with the most readily available materials. The
heat and smells generated by decomposing
faecal matter in the latrine mean that latrines
often have large eaves, or might even lack a door
or roof in order to ventilate the latrine, thus
of ering easy entry to fl ies and mosquitoes. The
main advantage for vector control of latrines
without roofs is that the latrine will be less likely
to become a resting place for mosquitoes, which
prefer to rest in dark places. However, a small
study in southern Tanzania found the absence
of a roof in a latrine as the only signifi cant factor
associated with fl y breeding (Knudson, 2011).
One of the key factors determining vector
breeding and smell in a latrine is the presence or
absence of water in the pit of a latrine. Water
will enter the latrine either through a high
groundwater table, water used for anal cleansing
or as a result of faecal decomposition, which
produces CO 2 and water. In the case where a pit

is not free draining, water will slowly build up
over time. A study into dif erent forms of on-site
sanitation found dry pit latrines to be completely
free from emergent mosquitoes, in contrast to pit
latrines with free water levels where 25% of
sampled pits were found to be positive for
emergent mosquitoes, predominantly Culex
quinquefasciatus , the main vector of Bancroftian
fi lariasis, certain viral diseases and a major
nuisance mosquito (Curtis and Hawkins, 1982).
Dry pits were found to be more productive for fl y
breeding compared to wet pits, with 35% of dry
pits positive for emergent fl ies compared to 25%
of the wet pits (Curtis and Hawkins, 1982). The
most common fl y families associated with pit
latrine breeding are Psychodidae and Cal-
liphoridae (Curtis and Hawkins, 1982; Knudson,
2011), of which especially Calliphoridae, fi lth
fl ies, have been associated with the transmission
of faecal pathogens (Rozendaal, 1997). Some
households might cover the squat hole using
home-made devices in order to prevent fl y
breeding (Fig. 8.4); however, no studies are
known that have investigated the impact of such
home-made devices on fl y breeding.
Very little is known about the ef ects of
chemicals that are often administered to pits
either to slow down fi ll-up rates or to decrease
vector breeding. Anecdotal evidence from
Ghana and South Africa suggests that the use of
chemical additives is on the increase. In addition,
in many countries, especially in South-east Asia,
lime and ash are added to latrines in order to
reduce smells. Both products could lower the
moisture content and raise pH levels, and
thereby have an impact on vector breeding
within latrines, though no evidence is available
to confi rm this.

Ventilated improved pit (VIP) latrine
Bad smells, nuisance mosquitoes and fl ies
encountered when visiting a pit latrine often
deter people from using the facilities. In response
to these problems, the ventilated improved pit
(VIP) latrine was developed in the 1970s in
Zimbabwe. The VIP latrine dif ers from the
traditional pit latrine by a large ventilation pipe
placed vertically and inserted into the pit (Fig.
8.2b) (Mara, 1984). The wind blowing over the
top of the ventilation pipe sucks air out of the
pipe, drawing in air from outside the pit through