Disease Transmission

Question 1

Factors in Disease Dynamics

Answer 1

changing hosts, pathogens, vectors, environments; plus new emerging diseases

Question 2

How has disease changed in the US since the 1900s?

Answer 2

we have moved from more infectious causes of death (flu, pneumonia, TB) to more chronic disease (heart disease, cancer)

Question 3

5 Drivers of Infectious Disease Emergence

Answer 3

1. Climate Change
2. Global trade and travel
3. Migration, social unrest
4. Human Population Growth
5. Urbanization

Question 4

3 Types of Prevention

Answer 4

1. Primary
2. Secondary
3. Tertiary

Question 5

Primary Prevention

Answer 5

protect the uninfected to prevent development of disease (ex: vaccination, biosecurity measures, closed herds)

Question 6

Secondary Prevention

Answer 6

detect the preclinical cases to reduce severity/complications

Question 7

Tertiary Prevention

Answer 7

reduce the impact of clinical disease with treatments, therapies, and rehab

Question 8

John Snow and Cholera in London

Answer 8

in 1855+, was able to determine an unknown organism was transmitting through the water supply via an unknown mechanism by mapping out neighborhood pumps and deaths

Question 9

When did germ theory come about?

Answer 9

1890s

Question 10

DO you have to know the causative agent to do anything about disease spread?

Answer 10

No - outbreak can be stopped by understanding disease patterns without the knowledge of the causative agent

Question 11

Smith, Kilbourne, and Curtis

Answer 11

determined that cattle dying from Texas fever and the natural range of cattle ticks overlapped geographically, so hypothesized ticks caused disease - this was the first determination of an infectious arthropod vector; also established life cycle of the tick

Question 12

Babesia bigemina

Answer 12

agent transmitted by ticks that causes Texas Fever

Question 13

endemic

Answer 13

usual (habitual) occurrence of a disease within a given area (what are normal levels?)

Question 14

sporadic

Answer 14

separate/scatted disease incidents occurring at a low frequency

Question 15

epidemic/outbreak

Answer 15

more disease than expected for a given time and place

Question 16

pandemic

Answer 16

epidemic affecting several continents

Question 17

reservoir

Answer 17

any animal/arthropod/plant/soil/inanimate matter in which an infectious agent normally lives and multiplies

Question 18

nidus

Answer 18

localized reservoir that persists over a long time period

Question 19

vehicle

Answer 19

object/substance/non-receptive living being that serves as an intermediate in transmitting pathogen from host to host

Question 20

vector

Answer 20

a LIVING creature which acquires a pathogen from one living host and transmits it to another

Question 21

fomite

Answer 21

object/substance that by itself is not harmful but on which pathogens may be conveyed (a type of vehicle, technically)

Question 22

carrier

Answer 22

individual which harbors the organism and can infect others, but is not clinically ill

Question 23

incubationary carrier

Answer 23

preclinical, many organisms shed

Question 24

convalescent carrier

Answer 24

harbors and sheds organisms for a period of time following recovery

Question 25

transient carrier

Answer 25

subclinical but organisms are shed for variable periods of time

Question 26

chronic carrier

Answer 26

postrecovery animals who shed organism for a long period of time

Question 27

incubation period

Answer 27

time between exposure to pathogen and the onset of clinical signs

Question 28

latent infection

Answer 28

inapparent infection that has potential to develop signs of disease

Question 29

source of infection

Answer 29

animal/person/object from which an infectious agent passes immediately to the host

Question 30

Use

Answer 30

extrinsic host factor for animals synonymous with occupation in humans

Question 31

Husbandry

Answer 31

extrinsic host factor for animals synonymous with socio-economic status in humans (ex: nutrition, crowding, open or closed herds, ventilation, vax status, handling, etc)

Question 32

pathogenicity

Answer 32

ability to produce disease

Question 33

virulence

Answer 33

degree of pathogenicity, or the severity of a disease

Question 34

Case-Fatality Rate (CFR)

Answer 34

number of deaths among cases; way to evaluate agent virulence

Question 35

host range

Answer 35

range of hosts in which an agent can survive

Question 36

viability

Answer 36

ability of an infectious agent to survive in the "free" state, aka environment

Question 37

infectivity

Answer 37

ability of agent to lodge and multiply within the host; minimum number of infectious particles required to establish an infection

Question 38

infectiousness

Answer 38

ease with which the agent is transmitted from one host to another

Question 39

2 Ways to Measure Infectiousness

Answer 39

1. Secondary Attack Rate 2. Basic Reproduction Number (Ro)

Question 40

The Basic/Effective Reproduction Number (Ro)

Answer 40

measure of infectiousness of an agent in a totally susceptible population; the number of new cases a single case will generate during its infectious period

Question 41

What must the Ro be for a disease to die out/be removed from a population?

Answer 41

Ro less than 1

Question 42

Ro of Foot and Mouth Disease?

Answer 42

infinity (one of the most infectious animal diseases)

Question 43

Non-Pharmaceutical Interventions (NPI)

Answer 43

think COVID, when they made everyone stay home, no events, schools were closed, and everything was friggin lame

Question 44

Herd Immunity

Answer 44

resistance of an "at risk" population to an attack by a disease to which a large proportion of the members of the group are immune

Question 45

Most critical factor in herd immunity?

Answer 45

frequency of contact

Question 46

Can herd immunity still be achieved if new susceptible animals occurs?

Answer 46

no

Question 47

Horizontal Transmission

Answer 47

among "peers"

Question 48

Vertical Transmission

Answer 48

through generations

Question 49

Examples of Indirect Modes of Transmission (2)

Answer 49

common vehicle, vector

Question 50

Fragile infectious agents are best/only transmitted via what mode?

Answer 50

direct transmission

Question 51

Expiratory Droplets

Answer 51

produced by cough/sneeze, short airborne life, evaporate before hitting the ground; needs direct transmission

Question 52

Droplet Nuclei

Answer 52

evaporated remains of expiratory droplets/other fluids, they are truly airborne, small; via indirect tranmission

Question 53

Which is more infectious - expiratory droplets or droplet nuclei?

Answer 53

droplet nuclei (by about ten times)

Question 54

6 Requirements for Disease Spread

Answer 54

1. Causative agent capable of infecting host 2. Reservoir/source of agent 3. Mode of escape from reservoir or intermediate source 4. Mode of transmission to new host 5. Mode of entry to new host 6. Susceptible host

Question 55

disease

Answer 55

abnormality of structure and/or function that interferes with the well-being of an individual animal

Question 56

preclinical disease

Answer 56

not yet clinically apparent but destined to be

Question 57

subclinical disease

Answer 57

not clinically apparent and not destined to be