Lecture 13: Disease Reservoirs and Transmission

Question 1

Disease transmission is a result of interaction between

Answer 1

host, agent, and environment

Question 2

Infectious disease

Answer 2

disease caused by the invasion and multiplication of a living agent in/on a host

Question 3

Infestation

Answer 3

Invasion, but not multiplication of an organism in/on a host (fleas/ticks, some parasites)

Question 4

Contagious

Answer 4

disease transmissible from one human/animal to another via direct or airborne routes

Question 5

Communicable

Answer 5

disease caused by an agent capable of transmission by direct, airborne, or indirect routes from an infected person, animal, plant or a contaminated inanimate reservoir

Question 6

Zoonotic disease

Answer 6

disease that is transmitted from animals to humans

Question 7

Latent period

Answer 7

microbe is replicating but not yet enough for the host to become infectious

Question 8

Incubation period

Answer 8

microbe is replicating but not symptomatic yet.

Question 9

Does the incubation period always correlate with the latent period?

Answer 9

Nope

Question 10

Reservoir

Answer 10

• Habitat in which an infectious agent normally lives, grows, and mulitplies
• Maintain pathogens over time, from year to year or generation to generation

Question 11

How do pathogens make it so that animals become susceptible again and again

Answer 11

They mutate

Question 12

How do pathogens allow infections to occur after a short time period?

Answer 12

They evade immunity

Question 13

Balanced pathogenicity

Answer 13

Chronic infections with minimal symptoms

Question 14

Are all sick animals reservoirs?

Answer 14

Nope

Question 15

Three questions that you must answer yes to in order for soemthing to be a reservoir

Answer 15

1. Is it naturally infected with the pathogen?
2. Can the species of animal maintain the pathogen over time?
3. Can this source transmit disease to a new, susceptible host?

Question 16

Two main types of transmission

Answer 16

1. Vertical

2. Horizontal

Question 17

Two types of horizontal transmission

Answer 17

• Direct

- Indirect

Question 18

Vertical transmission

Answer 18

From a reservoir host to its offspring

Question 19

Congenital transmission

Answer 19

• Vertical

- Some pathogens can cross the placenta, infect eggs, ect

Question 20

Perinatal transmission

Answer 20

• Vertical

- During parturition, via colostrum

Question 21

Horizontal transmission

Answer 21

from reservoir to new host

Question 22

Direct horizontal transmission

Answer 22

Directly from the reservoir to a susceptible host

Question 23

Indirect horizontal transmission

Answer 23

Via any sort of intermediary, animate or inanimate

Question 24

Three types of horizontal/direct transmission

Answer 24

1. Direct transmission - contact
2. Direct projection - droplet spread
3. Airborne - Considered to be a form of direct

Question 25

Vehicle

Answer 25

Inanimate object which communicates the disease

Question 26

Vector

Answer 26

Living organism that communicates the disease

Question 27

Two types of vehicles

Answer 27

1. Common - food, water, contaminated IV drugs | 2. Fomites - object that can be contaminated and transmit disease on a limited scale (ex. door knob)

Question 28

Most vectors are

Answer 28

arthropods (mosquitoes, flies, fleas, ants, ticks)

Question 29

Mechanical vector

Answer 29

Agent does not multiply or undergo part of its life cycle while in/on arthropod

Question 30

Biological vector

Answer 30

Agent undergoes changes or multiplies while in the vector and these changes are required for transmission

Question 31

Emerging disease

Answer 31

- Previously unknown disease that suddenly appears | - Known disease that suddenly appears in a new population

Question 32

Re-emerging disease

Answer 32

-Known disease, previously on the decline, that is becoming more common and will likely continue to do so

Question 33

Exposure

Answer 33

- Introduction of a new agent into a susceptible population | - Exposure is caused by movement of infectious agents

Question 34

New pathogens originate from

Answer 34

old pathogens

Question 35

Transmission

Answer 35

- Adoption, establishment, and dissemination in the susceptible population - Requires a pathogen that can adapt to, and transmit between, these hosts

Question 36

7 determinants of emergence

Answer 36

1. Type of agent (pathogen) 2. Mutation/change (pathogen) 3. Phylogenetic distance (reservoir) 4. Reservoir size (transmission) 5. Pathogen prevalence (transmission) 6. Contact frequency (transmission) 7. Susceptibility (host)

Question 37

What percentage of human pathogens are zoonotic

Answer 37

61%

Question 38

What percentage of emerging diseases are zoonotic

Answer 38

75

Question 39

How likely are zoonotic diseases to be associated with emerging diseases?

Answer 39

Twice as likely

Question 40

What do mutations do for pathogens

Answer 40

- Increased antibiotic resistance - Increased virulence (transmissibility within or between species) - Evasion of host immunity

Question 41

Phylogenetic distance between reservoir and new host

Answer 41

- Best transmission is within species | - More likely to be crossed to closely related species

Question 42

Pathogens that cross very different species often cause

Answer 42

Very different, often more severe, disease

Question 43

Two reasons for new host susceptibility

Answer 43

- Intensive agriculture | - More populations with weakened immune systems

Question 44

Three factors that increase transmission

Answer 44

- Increasing abundance of reservoir - Increasing pathogen prevalence in reservoir - Increasing contact between the reservoir and new host