Database Reference
In-Depth Information
OUTFLOWS:
GET SICK
=
CONTACT RATE * (CONTAGIOUS
+
SICK)*NON IMMUNE
{
Individuals per Time Period
}
SICK(t)
=
SICK(t
−
dt)
+
(STAY IN BED
−
RECOVER
−
DIE) * dt
INIT SICK
=
0
{
Individuals
}
INFLOWS:
STAY IN BED
=
CONTAGIOUS
{
Individuals per Time Period
}
OUTFLOWS:
RECOVER
=
.9*SICK
{
Individuals per Time Period
}
DIE
=
.1*SICK
{
Individuals per Time Period
}
CONTACT RATE
=
.000002
{
1/(Number of Contagious
+
Sick) *
Nonimmune) per Time Period
}
2.4 Two Population Epidemic Model
Many diseases can affect different species and be spread from one species to another.
Notable examples include AIDS and Ebola. To concurrently capture the spread of
a disease within and between species, we will use a simplified version of our basic
model of Section 2.1 above. Let's first lump the CONTAGIOUS and SICK popula-
tions into one stock, and call it INFECTED and then define a SURVIVAL RATE,
which we set to 0.065. The flows SURVIVE and DIE are specified as
SURVIVE
=
SURVIVAL RATE
∗
INFECTED
(2.5)
DIE
=(
1
−
SURVIVAL RATE
)
∗
INFECTED
(2.6)
This is a rather lethal disease compared to the one in Section 2.1. The new model
is shown in Figure 2.6 and its dynamics are shown in Figure 2.7.
GET SICK
NON IMMUNE
INFECTED
DIE
BIRTHS
SURVIVE
CONTACT RATE
SURVIVAL RATE
Fig. 2.6
