Lecture 18: Disease Dynamics Flashcards
if Infectious disease
virus, bacteria, or other parasite that can be passed from one host to the next
showcase population dynamics
Infectious disease temporal patterns
Endemic: relatively small fluctuations
Outbreak: present but flaring up in outbreaks at frequent intervals
Epidemic: intense outbreaks followed by disappearance
How can we tell if a disease will become an epidemic?
Simple models can help us to understand
Classic Disease dynamics
As the disease progresses, susceptible population declines and d//dt (number of individuals infected changes over time) turns negative
Outbreak intensity depends on
R0
R0 = N β / γ
N= population size
β= transmission rate
γ= recovery rate
Decreasing the probability of a disease outbreak
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
Decreasing the probability of a disease outbreak S (susceptible individuals)
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!
Herd immunity
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
Polio Disease
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
Rare genetics diseases are more common in
small populations due to inbreeding
Infectious diseases increase with
population size
diseases spread more easily
more susceptible individuals, easier for disease to spread when populations are dense
Australian Rabbit infected with myxoma virus
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
Sharp outbreaks are actually bad for viruses too since it
can die out completely
If the curve flattens for disease,
new births are fast enough to replenish the susceptible pool in time, the disease can go and on (common cold virus, etc)
It is not really interest of virus “_____”, so this should be a ______
individuals, weak form of selection
It is not always the case that there are _____ tradeoffs between ____ and ____
physiological, transmission, virulence
Bacterial infection intervention: ideal scenario
Exposure to bacteria occurs
Infection occurs and bacteria spreads in the body
Drug treatment (antibiotic) is used and all bacteria die
Bacterial infection: antibiotic resistance (more complicated)
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
Why is it becoming more difficult to create new drugs?
Antibiotics are becoming more and more resistant
New promising ideas for creating drugs with antibiotic resistant by
outsmarting bacteria with AI
Individual optimum, group optimum conflict with antibiotic resistant
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
We must regulate antibiotic use,
appeal to morality of people to only take antibiotics when they are sure they need them
Ways for how should I use antibiotics to protect myself and my community from antibiotic resistance?
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
In summary you should not use antibiotics if you
if you do not need them
