Disease Reservoirs and Transmission

Question 1

Disease transmission is a result of the interaction between what 3 things?

Answer 1

1. The host
2. The agent
3. The environment

Question 2

Who is considered the Father of Epidemiology?

Answer 2

John Snow

Question 3

What did John Snow publish in 1849?

Answer 3

Evidence that cholera is transmitted by fecal-oral route and by the water supply.

Question 4

What is this?

Answer 4

A spot map: with most of it’s concentration at the center.

John Snow created it to show that a well pump was the source of cholera in London.

Question 5

Robert Koch first isolated which bacterium to prove what?

Answer 5

Bacillus anthracis to prove that it really causes anthrax.

This was the beginning of the modern germ theory.

Question 6

Louis Pasteur developed and tested early ______ in sheep, goats and cattle.

Answer 6

Vaccines

Question 7

Who was Typhoid Mary?

Answer 7

She was an asymptomatic carrier of Salmonella typhi that caused outbreaks of Salmonella wherever she went/cooked. She was forcibly quarantined for most of her life.

Question 8

In 1897 Ronald Ross discovered what?

Answer 8

That mosquitoes transmitted malaria.

Question 9

In 1900, Walter Reed discovered what?

Answer 9

That mosquitoes transmit Yellow Fever.

Question 10

Disease transmission can be represented by a _______ ____ ______.

Answer 10

Chain of events.

Chain of Infection

Question 11

What is a reservoir?

Answer 11

Habitat in which an infectious agent normally lives, grows and multiplies (humans, animals or the environment.)

Reservoirs maintain pathogens over time, from year to year ot generation to generation.

Question 12

When trying to recognize a reservoir, what 3 questions should you be asking yourself?

Answer 12

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

Question 13

With regard to Trichninella, pigs and bears are considered to be what type of host?

People are considered what type of host?

Answer 13

• Pigs and bears* are reservoir hosts.
• People* are accidental hosts.

Question 14

Pathogens mutate to escape immunity so that animals become _______ again over time.

Answer 14

Susceptible

Question 15

Pathogens can evade immunity, allowing _________ to occur after a short period of time.

Answer 15

Reinfection

Question 16

Pathogens can cause chronic infections with minimal symptoms called what?

Answer 16

Balanced pathogenicity

Question 17

Infection does not equal ______ which does not equal ________.

Answer 17

Infection does not equal disease which does not equal infectivity.

Question 18

Clinically ill animals that are reservoir competent are probably what?

Answer 18

Infectious

• But so are asymptomatic carriers…*
• However not all ill animals are reservoirs.*

Question 19

What are the 2 major types of transmission?

Answer 19

Horizontal and Vertical

Question 20

What is vertical transmission?

Answer 20

From reservoir host to offspring.

Can be congenital: some pathogens can cross the placenta, infect eggs, etc.

Can also be perinatal: during parturition or via colostrum/milk.

Question 21

What is horizontal transmission?

Answer 21

From the reservoir to a new host.

Can be direct: directly from the reservoir to a susceptible host.

Can also be indirect: via any sort of intermediary, animate or inanimate.

Question 22

Horizon/Direct Transmission can occur 1 of 3 ways which are what?

Answer 22

1. Direct contact
2. Direct projection
3. Airborne

Question 23

What is direct contact?

Answer 23

Skin-skin contact, mucous membrane contact (including sexual transmission), direct contact with a soil reservoir (bite, scratch, etc…)

Question 24

What is direct projection?

Answer 24

Droplet spread.

Wet, large and short range aerosols (sneezing, coughing, or talking.)

Question 25

What is airborne transmission?

Answer 25

This is considered to be a form of direct transmission because disease agents do not generally survive for extended periods within aerosolized particles.

Question 26

What is a vehicle?

Answer 26

An inanimate object that can indirectly spread disease.

ex: Food, water, contaminated IV drugs, fomites: farm boots, surgical tools, or an actual vehicle (such as a tractor).

Question 27

What is a vector?

Answer 27

A living organism (mostly arthropods) that serves to communicate disease indirectly.

2 types: mechanical or biological

• Mechanical= the agent DOES NOT multiply or undergo part of it’s life cycle while in/on the arthropod.*
• Biological= the agent undergoes changes or multiplies while in the vector; these activities are required for transmission.*

Question 28

What type of disease transmission is Lyme Disease?

West Nile Virus?

Answer 28

Horizontal indirect transmission

same as Lyme Disease for WNV.