Lecture 18: Disease Dynamics

Question 1

if Infectious disease

Answer 1

virus, bacteria, or other parasite that can be passed from one host to the next
showcase population dynamics

Question 2

Infectious disease temporal patterns

Answer 2

Endemic: relatively small fluctuations
Outbreak: present but flaring up in outbreaks at frequent intervals
Epidemic: intense outbreaks followed by disappearance

Question 3

How can we tell if a disease will become an epidemic?

Answer 3

Simple models can help us to understand

Question 4

Classic Disease dynamics

Answer 4

As the disease progresses, susceptible population declines and d//dt (number of individuals infected changes over time) turns negative

Question 5

Outbreak intensity depends on

Answer 5

R0

R0 = N β / γ

N= population size
β= transmission rate
γ= recovery rate

Question 6

Decreasing the probability of a disease outbreak

Answer 6

R0 = N β / γ ; if R0 < 1 outbreak not likely

Decrease N: decrease number of interacting individuals in a population

Decrease β (transmission efficiency): wear a mask, wash hands, stand over 6 feet apart

Increase γ (decrease time period of infecting others): stay home when you are sick, get tested and stay home if you have the disease

Question 7

Decreasing the probability of a disease outbreak S (susceptible individuals)

Answer 7

dl/dt < 0 S β/γ <1
▪ S β/γ is the disease’s λ (rate at which susceptible individuals are exposed to the infection)

Decreasing S?
▪ Vaccination!

Question 8

Herd immunity

Answer 8

Some individuals never get the disease because when enough individuals are recovered and no longer susceptible to it the disease cannot spread as well, λ falls below 1 and the disease dies out

but a lot of people still get the disease
this does not mean we just wait for disease to pass
it does mean vaccination does not have to be perfect to eradicate a disease

Question 9

Polio Disease

Answer 9

Causes paralysis
A vaccine became available in 1955
Vaccines have been successful at decreasing Polio
It’s thought possible that we could have completely eradicate it
But when vaccines drop it can resurge

Question 10

Rare genetics diseases are more common in

Answer 10

small populations due to inbreeding

Question 11

Infectious diseases increase with

Answer 11

population size

diseases spread more easily
more susceptible individuals, easier for disease to spread when populations are dense

Question 12

Australian Rabbit infected with myxoma virus

Answer 12

Eye is shut closed
Take sample of virus in different epidemics experienced by the population
Variation in lethality correlated with epidemic number
Evolution of lower lethality is beneficial to virus
Lower lethality decreases gamma (recovery rate)
Individuals are infected for longer and the disease can spread more effectively

Question 13

Sharp outbreaks are actually bad for viruses too since it

Answer 13

can die out completely

Question 14

If the curve flattens for disease,

Answer 14

new births are fast enough to replenish the susceptible pool in time, the disease can go and on (common cold virus, etc)

Question 15

It is not really interest of virus “_____”, so this should be a ______

Answer 15

individuals, weak form of selection

Question 16

It is not always the case that there are _____ tradeoffs between ____ and ____

Answer 16

physiological, transmission, virulence

Question 17

Bacterial infection intervention: ideal scenario

Answer 17

Exposure to bacteria occurs
Infection occurs and bacteria spreads in the body
Drug treatment (antibiotic) is used and all bacteria die

Question 18

Bacterial infection: antibiotic resistance (more complicated)

Answer 18

Different individuals and bacteria in your body with some variation
Mixed bacteria population infects person
Antibiotics kill non resistant bacteria
Resistant bacteria multiply
Resistant bacteria spread and infect a new person
Antibiotic fail to kill resistant bacteria

Question 19

Why is it becoming more difficult to create new drugs?

Answer 19

Antibiotics are becoming more and more resistant

Question 20

New promising ideas for creating drugs with antibiotic resistant by

Answer 20

outsmarting bacteria with AI

Question 21

Individual optimum, group optimum conflict with antibiotic resistant

Answer 21

If you think you are sick with bacteria, low risk for you to take antibiotics
If everyone takes antibiotics all the time, the community is likely to have many antibiotic resistant strains and the medicine will work on no one

Question 22

We must regulate antibiotic use,

Answer 22

appeal to morality of people to only take antibiotics when they are sure they need them

Question 23

Ways for how should I use antibiotics to protect myself and my community from antibiotic resistance?

Answer 23

Ask you healthcare professional ways to feel better without use of antibiotics
Take prescribed antibiotic exactly as your healthcare professional tells you
Never taken antibiotic for viral infection (cold, flu)
Never take antibiotics prescribed for someone else
Never save antibiotics for next time you get sick

Question 24

In summary you should not use antibiotics if you

Answer 24

if you do not need them