Pattern formation for a partial immune system modeling the spread of an epidemic disease

Mazen Saad
in collaboration with Mostafa  Bendahmane

Our motivation is a mathematical model describing the spatial propagation of an epidemic disease through a population. In this model, the pathogen diversity
is structured into two clusters and then the population is divided into eight classes which permits to distinguish between the infected/uninfected population with respect to clusters. In this paper, we prove the weak and the global existence results of the  solutions for the considered reaction-diffusion system with Neumann boundary. Next,  mathematical Turing formulation and numerical simulations are introduced to show
the pattern formation for such systems. For more information see here. 

A system of reacting and diffusing chemicals can interact and produce a stable nonuniform patterns in space.
Diffusion is usually considered to be a stabilizing process, but Turing's idea is, under certain conditions (Turing conditions),
spatially inhomogeneous patterns can evolve by diffusion driven instability.

We are  concerned with the formation of steady state spatially heterogeneous spatial patterns for a simple model of partial immunity model.
Turing conditions are exhibit for this model. Numerical results show that a random perturbation around the steady uniform state in the absence of diffusion can
generate a stationary nonuniform spatially state when the diffusion are included.

Partial immunity and spatial diffusion: The host population is divided into three proportions: susceptible (u); infected (v); and recovered with reduced
susceptibility (w). The partial immunity model is build under the assumption that individuals who have been previously infected and recovered can be reinfected at a reduced rate.


TEST 1. One steady mode : stripes and strikes pattern

Consider the initials conditions :
u(0,x,y)=u0(1+0.1 cos(3.14 n x) cos(3.14 m y))
v(0,x,y)= v0 (1+0.006 cos(3.14 n x) cos(3.14 m  y) )
w(0,x,y)=1-u(0,x,y)-w(0,x,y)

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Patterns for Susceptible (left), Infectious (center) and recovered (right)
with   initials conditions with n=m=2.

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Patterns for Susceptible (left), Infectious (center) and recovered (right)
with   initials conditions with n=4, m=0.




TEST 2 : Interaction between several modes

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Initial conditions with random perturbation around steady solution
Initials densities for Susceptible (left), Infectious (center) and recovered (right)


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Random perturbation around steady solution. Pattern formation for
Susceptible (0.1387 <= u <= 0.1418) (left) , Infectious (0.0778 <= v <= 0.0960) (centre)
and recovered  (0.7728 <= u <= 0.7748) (right) at time T= 0.025.



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Random perturbation around steady solution.
Pattern formation for Susceptible (0.1143 <= u <= 0.1535) (left),
Infectious  (0.0015 <=v <= 0.2072) (center)
and recovered (0.7638 <= u <= 0.7975) (right) at time T= 1.