Bio 418 Unit 1

A bunch of random questions to test vocab and fundamental concepts!

Define latent period

The time between when a person gets infected to when they are infectious (think infectious L(atent)aughter)  

Define incubation period

The time between when a person gets infected to when they are symptomatic (think i for itchy symptoms)

Define generation time

The total period of infection

T/F The latent and incubation period are always aligned

False, they can overlap and one can be shorter/longer than the other

What would a long latent period and short incubation period indicate?

a. Infected people will be infectious very quickly, and show symptoms very quickly

b. Infected people have a long time before they are infectious, and won’t show symptoms for a while

c. Infected people will be infectious very quickly, but won’t show symptoms for a while

d. Infected people have a long time before they are infectious, but show symptoms very quickly

d.

T/F Generation time describes infectiousness

False, it just describes infection time

Describe the difference between a micro/macro parasite

Microparasites are pathogens that replicate within the host, macroparasites are parasites that replicate outside of the host

Define infection

An invasion of a host by a transmissible communicable agent

Define disease

The clinical manifestation of an infection (symptoms)

Why is “infectious disease” an inaccurate statement?

An infection can cause a disease (physical symptoms), but it can also be asymptomatic. The pathogen is infectious, not the disease. (You don’t catch a sneeze from someone who has a cold, you catch the virus causing it.)

Define incidence

The rate of new infections in a population

Define prevalence

The proportion of a population that is infected (PPP: prevalence, proportion, population)

Prevalence = ? x ?

Incidence x duration

T/F Incidence is always a rate

True

T/F Prevalence is a rate in a population

False

Would four new infections describe prevalence or incidence?

Neither it’s not a rate or a proportion

In a closed system, when prevalence remains constant what does that tell you about infections and deaths?

No new infections and no new deaths

Looking at a graph, what would an increase in incidence do to the prevalence curve?

It would increase it since the proportion of infected people grew

T/F On a closed system graph, if incidence drops prevalence will immediately also drop

False, the amount of people who are infected hasn’t changed, but it will decrease over time as people enter recovered

Define epidemic

A rapid, unexpected rise in the prevalence of a pathogen in a region

Define endemic

Little variation in the presence of that pathogen in a region

Define disease dynamics

The change in infection abundance across space and time

T/F The pathogen determines whether it’s epidemic or endemic worldwide

False, a pathogen can be an epidemic in some regions but endemic in others.

What determines whether a pathogen is endemic or epidemic

Transmission dynamics, changes in host population or pathogen characteristics

T/F Once a region experiences an epidemic it will always be an epidemic there

False, the region can become endemic if the pathogen becomes stable again

Define these variables N = S+I+R

N = total population

S = susceptible population

I = infected population

R = recovered/removed population

What happens to N in a basic SIR model?

It remains constant

What causes people to leave the susceptible compartment?

Immunization or infection (and death unless it’s closed)

What causes people to leave the infected compartment?

Recovery or death

T/F In an SIR model (where immune stay in recovery) people move unidirectionally in the model

True

What is β? What is it the product of?

Transmission rate, the product of probability of contact between S and I and the likelihood of a transmission event at SI contact

What does a cross mean in an SIRS model

Death

What is the difference between an SIR and SIRS model

SIR assumes permanent immunity, SIRS accounts for lost immunity

Match the following action to the SIR compartment for a transmission bottleneck:

1. Isolate

2. Immunize

3. Quarantine

Quarantine S, isolate I, immunize S to R

Define herd immunity

Threshold of immunity for indirect protection of people’s contacts

Define R0 (aka basic reproductive number)

The average number of people that a single infected individual will infect in a completely susceptible population (try to memorize this)

What factors influence R0

Pathogen characteristics, host population characteristics, and the environment

T/F R0 accounts for outliers

False

T/F R0 includes a population with immunized, but not recovered people

False, includes neither

T/F R0 is theoretical

True

What does a high R0 mean

The pathogen is a good transmitter

What pathogen has the highest R0

Measles, R0 of 12-20

Define Re

Average number of people one infected person will infect in a population with immunity

What’s the difference between Re and R0

R0 is theoretical with no immunity, while Re is the actual number with immunity

T/F Re is what R0 effectively is

True

What happens to Re as immunity increases?

It decreases (since there are less people to infect)

What happens when R0 is less than 1 (typically)

Transmission bottleneck → the number of infected people declines → the pathogen will eventually fadeout

T/F Pathogens can still persist if their R0 is less than 1

True, polio is an example of this

What does an epidemic curve represent? What is it determined by?

Number of new cases overtime, determined by latent and infectious period

T/F In an epidemic curve the light gray area is the minimum of the latent period

True

What is the herd immunity threshold equation

Pc = 1 -(1/(R0))

Define eliminated

A disease that has been removed from a region

Define eradicated

A disease that is removed worldwide

T/F You can eliminate diseases you can’t eradicate

True

T/F You cannot eliminate a disease without eliminating the pathogen

False, you can remove disease without the pathogen (like polio, or rabies in dogs)

Define direct transmission

A pathogen is passed directly from host to host

Define indirect transmission

Pathogen passed through intermediate contact

Select all that are examples of direct transmission

a. sexual transmission

b. water transmission

c. airborne transmission

d. nonspecific (surface/fomite) transmission

a, c, d

Select all that are examples of indirect transmission

a. environmental transmission

b. water transmission

c. bloodborne transmission

d. soil transmission

a, b, d

What are the three components of the epidemiological triangle? What do they explain?

Environment, host, pathogen; together they explain disease ecology

Give three examples of environment factors

Population density, landscape, political/economic resources, access to resources

T/F There is no correlation between GDP and % of deaths caused by preventable diseases

False

What are two major consequences of removing stable services that fight preventable diseases?

Removes trust in a population and increases cases of preventable disease

Define horizontal outreach

A public health strategy focusing on large issues that indirectly address multiple smaller problems. (think of a blanket being spread horizontally to encompass all of the problems)

Define vertical outreach

A public health strategy that focuses on only one aspect of a problem. (think of a vertical finger only pointing at one thing)

What is a criticism of verticle outreach?

It doesn’t address the underlying cause of the problem it’s solving

The smallpox vaccination campaign is an example of which outreach type

Vertical

List two horizontal outreach examples

Improving health care, water sanitation, targeted education programs, food programs

What contributed to the 2009 Burkina Faso measles outbreak?

• The true population size was unknown

• The calculated threshold for herd immunity was incorrect (because of above)

• Large pool of susceptible people accumulated

What is the infectious agent of smallpox? How is it transmitted?

Variola major/minor, directly transmitted, airborne and fomites

What genus does smallpox belong to

orthopox

T/F The smallpox virus is single stranded, which makes it less stable

False, it’s double stranded which makes it stable

Which smallpox variant (V. major or minor) is more severe?

V. major

T/F Smallpox has an animal reservoir

False, it only has human to human transmission

What does cross-immunizing mean

Getting one strain of a pathogen means you’ll be immune to another strain

T/F Pathogens in the orthopox genus (smallpox, cowpox, etc) are cross immunizing

True

What observation was made about dairy workers that were infected with cowpox?

They were immune to smallpox

What do vaccines do?

Prime the immune system for an antigen with a weakened (inactivated or attenuated) version of a pathogen

What is variolation? Why was it important?

A method for infecting people with smallpox by exposing them and inducing immunity. This reduced the fatality rate since the amount of virus was smaller and more controlled.

List aspects of “pathogen” for smallpox that helped eradicate it

• human to human transmission (no animal reservoirs)

• strongly immunizing

• cross immunizing

List aspects of “host” for smallpox that helped eradicate it

• cross immunity

• lasting immunity

• early onset of recognizable symptoms

List aspects of “environment” for smallpox that helped eradicate it

• thermostable vaccine

• bifurcated needle needed

Why was a thermostable vaccine important for smallpox?

It didn’t require a cold chain so it could reach remote places

Why was the bifurcated needle important for smallpox?

It required minimal training, and left an identifying scar

What vaccination technique helped the eradication of smallpox? Explain it.

Ring vaccination, when one person gets infected, you vaccinate everyone around them to prevent the spread

What were some of the ethical concerns about the smallpox vaccination campaign?

• vaccinators were forceful with their vaccinations, they didn’t always ask for consent

• no other help was given to communities, vaccinators came in, vaccinated, then left

Define spillover

When a pathogen jumps from an animal host to a human host

What are some differences between mpox and smallpox

Mpox is less severe, and is a spillover from monkeys

What contributed to the mpox outbreak in 2017?

• low vaccination rate against smallpox

• sustain transmission through marginalized populations like gay men

What genus does measles belong to

morbillivirus  

T/F Measles is highly transmissible, strongly immunizing, and directly transmitted

True

T/F Measles is double stranded, making it very stable

False, it’s single stranded making it unstable

What impact does measles have on the immune system after an infection?

Lose diversity and specificity of antibodies, basically resets immune system to 0 which is especially dangerous for kids

How does school affect the seasonality of measles?

Higher rates when school starts, with a drop over winter break

Define term-time forcing

the increase in childhood disease transmission associated with kids going back to school

Why do measles outbreaks typically skip a year?

To allow time for the susceptible pool to replenish

Define persistence

The proportion of weeks a disease is absent from a population

What does the Bartlett model describe

how local population size affects pathogen persistence

What would low measles persistence indicate

High amount of yearly measles

Would a large city population be more likely to have epidemic or endemic measles? What about a small town?

• Large town would be endemic: higher population → higher birth rate→ consistent susceptible population→ consistent outbreaks.

• Small town would likely be epidemic: lower population → lower birth rate → growing susceptible population → one kid gets sick → entire town gets sick in an epidemic