BIOL 437 Week Five Part 1

Question 1

reproductive number (R.)

Answer 1

• average number of secondary infections generated by the first infectious individual in a population of completely susceptible individuals
• continues until something slows the process down

Question 2

R. affects

Answer 2

-rate of spread

Question 3

R. increases with

Answer 3

• length of infection (L)

- longer a person is infected=longer they can transmit to other people

Question 4

S

Answer 4

• number of susceptible hosts that can be infected

- higher=greater potential for first individual to transmit infection

Question 5

L+S

Answer 5

-determines the potential number of contacts over the course of an infection

Question 6

R. also depends on

Answer 6

-how transmissible a pathogen is

Question 7

transmissibility depends on

Answer 7

-pathogen
-population of interest
>nutrionally stressed are more susceptible
*beta

Question 8

outbreaks

Answer 8

• only likely to spread if R. is >1

* threshold for that pathogen

Question 9

interventions to reduce R. threshold

Answer 9

1. Decrease number of susceptible individuals
   >vaccination
2. Decrease the length of time an individual is infectious
   >ask sick people to stay home
3. Decrease transmissibiilty
   >limit contacts or introduce sanitary measures

Question 10

epidemics

Answer 10

-mostly associated wiht acute, highly transmissilbe, directly transmitted pathogens

Question 11

SIR compartmental framework

Answer 11

• susceptible, infected, removed
• used to understand epidemic curves caused by these pathogens
• removal is either due to death or recovery with immunity
  ex. smallpox, measles

Question 12

epidemic curve: SIR

Answer 12

-assumes random interactions
-speed of transmission depends on the R. and the infectious period
>higher R., shorter infectious period = more explosive spread

Question 13

effective reproductive number (Re)

Answer 13

• average number of new infections later in an epidmeic
• R. x individuals still susceptible
• if less than 1, epidemic is self-limiting

Question 14

self limitation

Answer 14

-outweighs contagion when proportion of susceptible falls below 1/R
>when population reaches ‘herd immunity’

Question 15

early in a new infectious disease

Answer 15

-Re will be close to R.

Question 16

pace of epidemic determined by

Answer 16

• duration of the infectious period
• latent period
• eg. season flu is typically self-limiting after a month or two

Question 17

population close to extinction

Answer 17

• due to acute, directly transmitted pathogens

- close to extinction but rarely to extinction due to the self-limiting nature

Question 18

characteristics that increase chance of host extinction

Answer 18

• also reduce pathogen self-limitation
• alternative, resistant hosts that act as a reservoir
• vector transmission

Question 19

determinants of susceptibility beyond immune status

Answer 19

1. Genetics
2. Microbiome
3. Nutrition

Question 20

positive social influence on immunity

Answer 20

-instrumental support
-emotional support
>higher=slower disease progression

Question 21

negative social influences on immunity

Answer 21

• social stressors (ex. loneliness)
• smoking
• drinking
• activate stress symptoms that depress or disrupt immune functioning

Question 22

force of infection

Answer 22

• way to measure degreee to which an infected individual can spread infection to susceptible individuals
• per capita rate at which susceptible individuals contract infection

Question 23

factors that affect force of infection

Answer 23

1. Transmissiblity

2. Prevelance of pathogen

Question 24

high force of infection

Answer 24

-immunizing infection
>see infection in younger people
-pathogens with higher R.

Question 25

low force of infection

Answer 25

-lower transmissibility
>lower contact rates
-individuals will be older on average by time of first exposure
-pathogens with lower R.

Question 26

force of infection relationship

Answer 26

-between mean age of infection in a population and basic reproductive number