History & Concepts of Infectious Disease (1/4)

Question 1

What is a pathogen?

Answer 1

Any microorganism that is capable of causing disease in a susceptible host. Can be primary (cause disease in normal host) or opportunist (causes disease in immunocompromised host)

Question 2

Infection

Answer 2

The ability of microorganisms to invade tissue, find conditions that are suitable for growth and replication, and stimulate an immune response

Question 3

Colonization

Answer 3

Establishment of an ecological niche for an organism, survival and replication without actual tissue invasion i.e. commensal (where the bacteria lives in us but doesn’t affect us)

Question 4

Intoxication

Answer 4

Agents that cause disease by elaboration of toxin sometimes without the presence of viable bacteria

Question 5

Virulence

Answer 5

The severity of the disease caused by the agent i.e. rabies is uniformly fatal but the common cold has minor symptoms

Question 6

Virulence determinant

Answer 6

a bacterial component/product that contributes to the ability of a pathogen to cause disease (may be chromosomal/moveable genetic elements i.e. plasmids)

A virulence determinant may be species, organ, or disease specific

Question 7

What’s an example of a variety of bacteria able to cause the same disease syndrome?

Answer 7

Sepsis

Note that a single bacteria/viral species can cause a multitude of diff disease

Question 9

What are the 4 categories of human infection?

Answer 9

Asymptomatic

Active (overt disease)

Incubatory (incubating but no symptoms. still can be infectious)

Latent (pathogen persists in tissue w/out symptoms i.e. HIV, TB, herpes)

Question 10

What are 4 major sources of reservoirs for bacterial pathogens?

Answer 10

Human (most common), animals, soil, water

Knowing the source of exposure & reservoir helps you identify the likely pathogen

Question 11

Endogenous v exogenous infection

Answer 11

Endogenous fomes from within the host (i.e. host becomes immunocompromised, enters a formerly sterile site, or ab’s alter normal flora)

Exogenous comes from outside the host (can be vertical or horizontal transmission)

Question 12

What are the 4 main ways that pathogens can cause host damage?

Answer 12

1. directly cause tissue damage i.e. with proteolytic enzymes
2. induce an excessive immune response resulting in damage i.e. endotoxin -> cytokines
3. cause a hypersensitivity reaction i.e. in endocarditis w/immune complex glomerulonephritis
4. malignant transformation of host cells i.e. in Hep B

Question 13

What are the 5 steps necessary for infection?

Answer 13

1. adherence & colonization
2. evasion of host defense
3. invasion: ability to invade tissues or cells
4. interference with host response: mimic/coopt host defense mechansms & use them to invade tissue
5. host tissue damage