Sanitation and Vector Control - Biological and Environmental Control of Disease Vectors - page 145

practise open defecation, or have a form of
sanitation that does not use water to transport
the excreta, small amounts of water, normally
ranging from 0.1 to 0.5 l, are added to the
excreta through anal cleansing. When water is
used to transport excreta to a nearby pit or septic
tank, the amount of water required depends on
the form of sanitation used; a pour fl ush latrine
might require only 3 l per fl ush, while a
conventional WC might require 25 l of water to
transport the excreta. In the case of a sewerage
system, human excreta are not only mixed with
water for fl ushing and/or anal cleansing (so
called black water), but also with greywater,
which includes all the other wastewater from
running a household, for example from
bathrooms, kitchens and household compounds.
In order to prevent blockages, water-borne
sewerage needs to operate with minimum water
use, which is often set at 20 l of water per fl ush.
The association between sanitation, vectors
and disease is through two main routes. The fi rst
route of transmission occurs via mechanical
arthropod vectors that transport faecal
pathogens on their body parts to human
dwellings. The second route is through the
provision of breeding sites as the mixture of
excreta and water of ers a perfect environment
for the immature stages of some mosquitoes,
fl ies and cockroaches to develop and mature.
Skatole (3-methylindole), found in excreta, is a
powerful attractant for fl ies (Brown et al ., 1961;
Mulla et al ., 1977) and Culex mosquitoes, and
mediates oviposition behaviour (Millar et al .,
1994; Barbosa et al ., 2010). Although Culex
mosquitoes serve as vectors of many pathogens,
such as arboviruses and helminths, they are not
implicated as mechanical vectors of faecal
pathogens to humans and only use the dif erent
forms of sanitation as breeding sites. The
following section will focus on the association of
cockroaches and fi lth fl ies with faecal-oral
transmission of disease.

foods. They are active during the night, and are
found in dark and preferably moist places, which
can include sewer drains, septic tanks and pits of
latrines, during the day. Cockroaches have been
found positive for diarrhoea-causing pathogens
(including cholera and typhoid fever). Cock-
roaches collected from a paediatric hospital
ward in Malaysia were examined for the presence
of dif erent bacterial pathogens, and 101 out of
104 cockroaches analysed were found to be
positive for at least one bacterial strain in their
gut (Oothuman et al ., 1989). A study in France
investigated the diversity of bacteria present on
cockroaches collected from dif erent settings,
including hospital nursing and out-patient
areas, swimming pool sides and toilets, low-
income fl ats and food-handling places. The
greatest diversity of bacterial fl ora on cock-
roaches was found at food-handling places,
toilets and low-income fl ats (Rivault et al .,
1993). Cockroaches have also been found to be
carriers of leprosy, plague and viral diseases
such as poliomyelitis. In addition, exposure to
cockroaches might also play an important role
in allergies and asthma, particularly in children
(Roberts, 1996; Huss et al ., 2001).
Despite these fi ndings, the role of cock-
roaches in the (mechanical) transmission of
gastrointestinal disease is unlikely to play
anything more than a minor role, especially
when compared to poor hygiene, water quality
and limited access to sanitation (Rozendaal,
1997).

8.2.2 Filth fl ies

Synanthropic fl ies, more commonly known as
fi lth fl ies, include the families Muscidae,
Calliphoridae and Sarcophagidae. They are
frequently found around human dwellings, and
have the potential for pathogen transmission as
they land and feed on household waste, faeces
and food. The most widespread fi lth fl ies are the
common housefl y Musca domestica , the bazaar
fl y Musca sorbens and the oriental latrine blowfl y
Chrysomya megacephala (Crosskey and Lane,
1993).
Female fl ies preferentially lay their eggs on
organic material, which includes human
excreta, garbage and manure, and feed on
human food and human secretions such as

8.2.1 Cockroaches

Cockroaches are among the most common pests
found in and around human dwellings
(Rozendaal, 1997). Cockroaches will feed on a
wide variety of foods, including human excreta,
but have a preference for starch and sugary