Week 12.3 Pathogenesis and Chain of Infection

Question 1

8 steps of pathogenesis

Answer 1

1. Exposure
2. Overcome barriers
3. Colonize the host
4. Acquire nutrients and grow
5. Avoid the innate immune system
6. Avoid the adaptive immune system
7. Exit the host
8. Systemic spread

Question 2

Mechanisms to evade immune response

Answer 2

1. Overcome physical barriers
2. Disruption of the innate response
3. Disruption of the humoral response

Question 3

Step 1: Exposure

Answer 3

The host must be exposed to the infectious agent

Question 4

Step 2: Overcome barriers

Answer 4

Infectious agent must overcome physical and chemical barriers

Question 5

What barriers do our bodies use?

Answer 5

-enzymes in mucus, tears, and saliva
-coughing and sneezing
-intact skin
-acid in sweat
-acid in stomach
-etc

Question 6

What is one strategy infectious agents use to overcome barriers?

Answer 6

Overwhelm the victim’s body with high numbers of infectious agent

Question 7

What is the infectious dose?

Answer 7

The minimum number of infectious agents required to cause an infection

Question 8

Why would the same infectious organism have two different infectious doses?

Answer 8

The method it uses to infect can have less or more barriers to overcome
Ex: broken skin vs. ingestion > broken skin is direct contact to an open wound and to bloodstream whereas ingestion has to go through mucus, saliva, acid in stomach, etc.

Question 9

Step 3: Colonize the host

Answer 9

Infectious agents use adhesins to bind to tissues

Question 10

What are adhesins?

Answer 10

-proteins that bind to specific receptors on the tissue surface
-often bound tightly to carbohydrates or proteins on the host cell’s surface

Question 11

Many pathogens are cell, tissue, and host specific because…

Answer 11

1. Attachment requires specific surface properties/receptors
2. Some parasites have specific growth conditions/portals of entry

Question 12

Step 4: Acquire nutrients and grow

Answer 12

-Destroying a cell releases macro and micro nutrients
-Growing on epithelial cells helps the pathogens compete with the host for nutrients
-Nutrient acquisition is almost ALWAYS related to the direct damage caused by the pathogen

Question 13

Yops general function

Answer 13

1. Disrupt the cytoskeleton (cell lysis)
2. Suppress immune response
3. Deliver other Yops

Question 14

Step 5: Avoid clearance by the innate immune system

Answer 14

1. physical barriers
2. chemical barriers
3. cellular defenses

Question 15

Step 6: Avoid clearance by the adaptive immune system

Answer 15

1. active immunity (natural or vaccination)
2. passive immunity (maternal or artificial)

Question 16

Example: Yersinia pestis mechanisms to avoid the immune response

Answer 16

1. Intracellular invasion (hiding)
2. Immune response modulation (disruption of immune system signaling)
3. Capsules (protects against phagocytosis and serum-mediated killing)
4. Plasminogen activator protease (protects against complement system)
5. Yops (kills attack cells)

Question 17

Step 7: Some members of the pathogen’s population must exit the host

Answer 17

This allows pathogens to spread their infection to other hosts

Question 18

Step 8: Systemic spread

Answer 18

If immune system cannot contain, tolerate, or remove a pathogen, the pathogen might spread throughout the body

Question 19

What is the chain of infection?

Answer 19

a conceptual model that describes how infections spread from person to person
1. Infectious Agents
2. Reservoirs
3. Portals of Exit
4. Modes of Transmission
5. Portals of Entry
6. Susceptible Host

Question 20

Infectious agent

Answer 20

-the thing causing the damage
-ex: bacteria, fungi, parasites, and prions

Question 21

Reservoir

Answer 21

-any place a parasite lives, reproduces, and/or grows
-ex: people, water, food

Question 22

Portals of exit

Answer 22

-the ways in which a pathogen leaves its host(s)
-ex: blood, secretions, excretions, skin, coughing/sneezing, and insect bite

Question 23

Mode of transmission

Answer 23

-the way in which an infectious agent moves from one reservoir to the next (thru diseases vectors)
-ex: physical, contact, droplets, airborne

Question 24

What are disease vectors?

Answer 24

Any agents which carry an infectious agent into a living organism

Question 25

Portals of entry

Answer 25

-the ways in which an infectious agent enters a host
-ex: mucus membrane, respiratory system, digestive system, broken skin, insect bite, placenta, vagina/penis, urethra, anus
-most parasitic diseases enter one or more of ten portals of entry

Question 26

Susceptible host

Answer 26

-any person at risk of acquiring an infection
-ex: immune deficiency, diabetes, burns, surgery, age

Question 27

What extrinsic risk factors contribute to susceptibility of a host?

Answer 27

-pathogen exposure
-immunosuppression (biologic therapy, immunomodulators, corticosteroids)