Disease Reservoirs & Transmission

Question 1

Disease transmission is a result of the interaction between _______,_______, and ______.

Answer 1

Host, agent, and environment

Note: The presence of these alone is NOT enough to cause disease

Question 2

Who used the “shoe-leather epidemiology” technique, by going door to door mapping the cases of cholera transmitted by the fecal-oral route and by the water supply in London?

A. Richard Dawkins
B. Louis Pasteur
C. Robert Koch
D. John Snow

Answer 2

D. John Snow

Question 3

Robert Koch first isolated this bacterium _________ and used experimental infection of naive animals to prove the the bacteria caused anthrax. Therefore supporting the “germ theory”.

Answer 3

B. Anthracis

Question 4

Who was an asymptomatic carrier that caused several outbreaks of typhoid fever (Salmonella Typhi = anthroponotic) between 1900-1915.

Answer 4

Typhoid Mary

• outbreak followed wherever she worked (she was a cook) and had to be quarantined for the rest of her life.

Question 5

________ discovered that malaria is transmitted by mosquitoes.

A. Laveran
B. Walter Reed
C. Ronald Ross
D. Louis Pasteur

Answer 5

C. Ronald Ross

Note: some credit the discovery to Grassi (Italian scientist)

Question 6

________ discovered that yellow fever is transmitted by mosquitoes. (1900)

A. Laveran
B. Walter Reed
C. Ronald Ross
D. Louis Pasteur

Answer 6

B. Walter Reed

Question 7

_______ (the French physician) discovered the agent plasmodium in 1880.

A. Laveran
B. Walter Reed
C. Ronald Ross
D. Louis Pasteur

Answer 7

A. Laveran

Question 8

True or False ?

In disease prevention, knowing the mode of transmission is generally more important than identifying the specific agent.

Answer 8

True

Note: This is where you make your interventions. The mode of transmission is very important, since you will not know the etiology right away.

Question 9

What are the 6 factors of the “chain” of infection ?

Answer 9

1. Host susceptibility
2. Pathogenic microorganism (bacteria, virus, parasite, fungus, prion)
3. Reservoir
4. Means of escape ( “Portal of exit”: cough, sneeze, feces, urine etc.)
5. Mode of transmission
6. Means of entry (Exposure)

Question 10

Define reservoir:

Answer 10

Habitat in which an infectious agent normally lives, grows, and multiplies (humans, animals, or the environment). Could be a living thing; the environment (soil, water)

• maintain pathogens over time, from year to year or generation to generation

Question 11

What is balanced pathogenicity ?

Answer 11

When the reservoir doesn’t get sick from the pathogens they carry

Question 12

What questions should you ask yourself when recognizing a reservoir ?

Answer 12

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

If you answered YES to all three of these the animal, soil, or water is a reservoir. Has to satisfy ALL three questions.

Question 13

If an animal has a disease it means it is a competent reservoir

True or False ?

Answer 13

False

Question 14

Why are reservoirs easy to miss ?

Answer 14

1. Elusive - can go years without being discovered
   - — Balanced pathogenicity (they don’t look sick)
   - — Persistence of infection
   - — Transmission may be sporadic
2. Role is often incompletely understood (lack of understanding)

Question 15

True or False

To eliminate diseases completely (eradication) control measures must be directed towards the reservoir ?

Answer 15

True

Question 16

True or False

Infection = Disease = Infectivity

Answer 16

False

They do not mean the same thing

Question 17

True or False

Clinically ill or asymptomatic animals that are reservoir competent are probably infectious.

Answer 17

True

Question 18

Vertical transmission

Answer 18

From a reservoir host to its offspring.

Congenital - pathogens crossing the placenta; infect eggs); (Perinatal - during parturition, via colostrum

Question 19

Horizontal transmission

Answer 19

From the reservoir to a new host

(Direct- directly form the reservoir to a susceptible host);
(Indirect - via any sort of intermediary, animate or inanimate object)

Question 20

Name some types of horizontal direct transmission:

Answer 20

1. Direct contact - skin-skin contact, bite, scratch
2. Direct projection (droplet spread) - sneezing, coughing or talking
3. Airborne - form of direct transmission; acts like a droplet. Disease agents do not generally survive for extended periods within aerosolized particles.

Question 21

What are the two types of horizontal indirect transmission ?

Answer 21

1. Vehicle - an inanimate object which serves to communicate disease. (Ex. Boots, medical supplies)
2. Vector - a living organism that serves to communicate disease (Ex. Tick, flea, mosquitos)

Question 22

Name some types of vehicles involved in the process of indirect transmission

Answer 22

1. Common vehicle -> food, water, contaminated IV drugs
2. Fomites -> objects that can be contaminated and transmit disease on a limited scale…knife, door knob, gloves. (Most nosocomial and iatrogenic infections are transmitted by fomites).

Question 23

Name and describe the two type of vectors

Answer 23

1. Mechanical = the agent DOES NOT multiply or undergo part of its life cycle while in/on the arthropod
2. Biological = the agent undergoes changes or multiplies while in the vector; these activities are required for transmission

Question 24

The first one to bring attention to the authorities is called an ______ ________.

Answer 24

Index patient

Question 25

What causes tularemia ?

Answer 25

Francisella tularensis ( Gram negative)

Note: not passed person to person
Transmission: Inhalation, ingestion, direct contact, mucous membranes, broken skin, vectors (Arthropoda;ticks)