Question

According to an S-I-R model, if a pathogen can kill its host

Select one:

a. the disease will not become an epidemic.

b. the individuals in the population will either die or become resistant.

c. the pathogen should increase in abundance until the hosts begin to die.

d. the pathogen should decrease in abundance until hosts begin to die.

Answer 1

As per the SIR (Susceptible - Infected - Recovery) model, the following equations describe the rates of suscetibility, infection and recovery.

if S is the number of susceptible population at time t.

I is the number of infected population at time t.

R is the number of recovered population at time t.

rate of population becoming susceptible

ds/dt = -bSI ......(1)

where, b is the fixed number of contacts per day to spread the disease.

rate of recovery

dr/dt = kI ........(2)

where, k is the fixed fraction of population that are recovered per day.

Thus, rate of infection

di/dt = bSI - kI .......(3)

If there is an increase in abundance of pathogen,

b >> k

Therefore, di/dt would be much greater than the rate of recovery

Hence, According to S-I-R model, if a pathogen can kill a host

The pathogens should increase in abudance until the hosts begin to die.