10 Infections 1-3

Question 1

Ecology

Answer 1

Ecology is defined as the “study of factors influencing the abundance and distribution of organisms.” For
infections in public health, the organisms whose ecology we are interested in are pathogens. Disease
ecology includes disease dynamics (changes in rates over time and location) as well as more general
interactions between pathogens and their environments and hosts

Question 2

Networks – difference between a random network and a scale-free network (which is more realistic for human societies?)

Answer 2

A random network is exactly what it sounds like: a lot of people/things randomly connected to each
other with no rhyme or reason. A scale-free network1
is where some nodes are more highly connected
than others (called hubs, colored gray in figure b, below). Human networks are scale-free. Random
networks are more hypothetical than real.

Question 3

Dynamics

Answer 3

how we describe infectious disease’ movements, patterns and behaviors over time and
geography.

Question 4

Herd Immunity

Answer 4

The ability of an agent to survive and infect many hosts in an environment depends on how well it can be transferred within that environment. When most of the hosts in the environment have a built up immunity to the agent it has less of a chance of successfully spreading and infecting members of the population.

Question 5

What are the fundamental modes of infectious disease transmission? (Be able to list 9 that were mentioned in the reading and describe what each one means in your own words)

Answer 5

airborne (respiratory droplets), water-borne, fecal-oral
(ingesting microscopic amounts of contaminated fecal matter), vector-borne (carried by non-host
species to host), fomite (touching surface, object or person), perinatal (mother to child), food-borne,
animal bites and sexual.

Question 6

What do the symbols S, I, and R stand for in the SIR model?

Answer 6

susceptible
infectious
recovered

Question 7

What do the symbols c, β (beta), λ (lambda), γ (gamma), and D stand for in calculations pertaining to the SIR model
Give a word or short phrase for each symbol

Answer 7

β = probability that a contact with an infectious person results in someone becoming infected, represented as P(infectious|contact) (you would say “the probability of becoming infectious, given that someone was contacted” if reading that notation)
γ= rate of recovery, the average duration is the reciprocal. (e.g. if each day 20% recover, then the reciprocal is 1/0.2 = 5. So the average time that someone is infectious is 5 days

Question 8

Also be able to explain the concept in your own words

Answer 8

For example, here is how you could give a short word or phrase for the symbol c, along with an explanation of the concept: the symbol c stands for “contacts,” meaning the average number of contacts that a person in a population would have with other people per day (or whatever time period we are considering); so c = 10 means that each person in the population has, on average, contact with 10 other people per day

Question 9

R0 – for now, just recognize that R0 = c × β / γ or R0 = c × β × D (because D = 1 / γ)

Answer 9

write equation

Question 10

be able to answer this question:
R0, the “basic reproductive number,” is the number of … what?

Answer 10

the number of new cases likely stemming from one infectious case
This is the number of infected individuals one person is expected to infect while they are infectious