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and the hypothesis that household cleaning can stop an outbreak from growing in
a village even while the water supply remains contaminated [
39
]. In exploring the
hypothesis, we first describe our physical space — we create a landscape with divi-
sions, e.g., households, schools, markets, etc., needed to simulate a village as well as
the water supply that is contaminated with the cholera-causing bacteria. We then cre-
ate our “agents,” the humans inhabiting the space, and define daily activities of these
agents within the village according to household, gender, and age. We incorporate the
ways in which the cholera-causing bacteria might spread through the community as a
result of fecal-oral contamination, including rules for how humans become infected
and how they in turn may contaminate their environment. From these relatively intu-
itive rules, a simulation is built from which global properties of the disease spread
emerge. Once satisfied that our basic simulation matches what is known about the
dynamics of cholera, we can explore options for decreasing the course of the disease.
In this ABM model, we introduce of household sanitation. We can test whether this
household change was able to affect the village-wide measure of numbers of people
who become ill. Because of the probabilistic nature of each simulation, each model
experiment is repeated many times to determine the “average” baseline behavior and
the “average” improvement with the sanitation effort.
4.3.1
Model Description
In the online materials we have included the NetLogo file “cholera.nlogo” which is
the result of the discussion herein. It may be helpful to open this file in NetLogo while
working through the model description that follows.
For the purposes of this initial exploration, we consider a simplified setting of
three extended households and one common space for our “village.” We additionally
make the simplification of ignoring gender- and age-specific activities or behavior.
We will assume that the village shares a water source that is contaminated with
cholera. The level of contamination can be varied in our simulations using the slider-set
parameter
environmental-reservoir
. Each household visits the water regularly,
and each household member is in contact with the contaminated water at “dinner.”
Each household has a sleeping area and a latrine area, and its residents are identified by
a common color. The configuration described above is also pictured with a simulation
screenshot in Figure
4.7
.
Cholera is known to spread in several ways [
37
]. There is generally a small chance
of contracting cholera from the local water supply. In fact, with the baseline choices
of parameters chosen for our simulation, the model generally runs for many “days”
before any inhabitants become infected. However, it is known that once one or two
people in a village contract cholera, they become active spreaders of the bacteria as
a result of shared contact with household objects and linens, and even by amplifying
the environmental contamination of the water supply due to a lack of sanitary latrines
[
37
]. Additionally, researchers have shown that the bacteria coming from freshly shed
feces, waste less than 5 h old, may be 700 times more infectious than is the bacteria
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