Lecture 7: Infectious Diseases

Question 1

What causes infection

Answer 1

bacteria, viruses, fungi, protozoa, prions

Question 2

what are the steps of infection

Answer 2

Chronologic sequence of events
Portal of entry
Regulated by virulence factors

Question 3

are most infectious agents targeting specific cells or organs

Answer 3

yes

Question 4

How does the infectious agent get into the body

Answer 4

Mucosae (respiratory, alimentary, lower urinary, reproductive, ear/eye)
Subcutaneous tissues

Question 5

what are the bodies cells that help to stop infectious agents initial multiplication

Answer 5

Macrophage, lymphocytes, dendritic cells

Question 6

where does the infectious agent go after initial multiplication

Answer 6

Then local (submucosa, subcutis), regional (lymph node), systemic spread

Question 7

what does the mucus protective layer of the body do

Answer 7

Prevents direct adherence
Blocks/traps organisms
Can facilitate action of phagocytes
Delivers antigens to local lymphoid tissue
Keeps antimicrobial substances and atb close to mucosa

Question 8

what can cause changes in goblet cell function and chemical composition of mucus that can lower protection

Answer 8

Dehydration
Shipping
Humidity
Ventilation
Weather changes

Question 9

how have microorganisms evolved to take advantage of our mucus protective layer

Answer 9

Source of food (carbohydrates, peptides)
If able to colonize inner mucus: prevents expulsion
Can specifically adhere to molecules in mucus
Microbial mucolysis ability is virulence factor

Question 10

how do you ingest an infectious agent

Answer 10

via infectious fomites

Question 11

where is the thickest layer of mucus protective layer

Answer 11

in the colon

Question 12

where is the thinnest layer of the mucus protective layer

Answer 12

in the jejunum

Question 13

what is located in the protective mucosal fluids

Answer 13

gastric acid, lyzozymes

Question 14

describe inhaling a fomite

Answer 14

Nostrils  Nasal turbinates, pharynx or lower airways
Depends on size, shape, weight
Virus > prions > bacteria > fungi > Protozoa
BUT mostly inhaled with fomites!
Air turbulence in turbinates increases deposition

Question 15

describe the mucuciliary apparatus

Answer 15

Biphasic mucus layer
Tip of cilia in gel
Nasal cavity & sinus:
Moves downward
Conductive respiratory:
Moves upward
Ultimately swallowed
Injury to epithelial cells (influenza, rhino) can disrupt and cause secondary bacterial infections

Question 16

describe infectious agent cutaneous penetration

Answer 16

Via abrasions, scratches, bite wounds, insect bite
Limited range of host targets
but limited defenses

Question 17

describe the pathogenicity of the infectious agents

Answer 17

Regulated by virulence factors
In bacterial genes
Their expression permits bacteria to 
Colonize mucosae, 
Infect cells,
Grow and replicate,
Cause cell death

Question 18

what infectious agents have good motility

Answer 18

spirochetes

Question 19

what infectious agents can digest the mucus layer

Answer 19

clostridium

Question 20

describe colonization of an infectious agent

Answer 20

Adhesion of sufficient amount of bacteria
Via:
Fimbria/Pilus
Adhesion molecules
Needs to be faster than cell renewal

Question 21

describe spreading of an infectious agent

Answer 21

Spreading
Destruction of collagen, tight junctions between cells
Provides safe spot for bacteria

Question 22

describe the toxins released by infectious agents

Answer 22

Exotoxins (gram +), endotoxins (gram -) (LPS: lipopolysaccharide)
Damages cells and extra-cellular matrix
Kills cells via cytolysis or activation of complement

Question 23

since Viruses are unable to produce energy and contain a limited number of enzymes what are they considered

Answer 23

obligate intracellular parasites

Question 24

how have viruses evolved

Answer 24

Have evolved to target specific cells in animals to sustain theirs needs
Not as many virulence factor
not as complex as bacteria.

Question 25

describe permissive viral target cells

Answer 25

Allows for viral replication

Question 26

describe non permissive viral target cells

Answer 26

no replication – used as reservoir

Can become permissive (ex with cell maturation or activation)

Question 27

describe step 1 of the viral replication cycle

Answer 27

1. Attachement and Entry
   Determines which organs are infected
   Viruses bind to normally expressed receptors

Question 28

describe step 2 of the viral replication cycle

Answer 28

2. Replication stage
   How much of the cell is hijacked
   Organelles, genome, other
   How much cell dysfunction, cell death

Question 29

describe step 3 of the viral replication cycle

Answer 29

3. Shedding
   How the virus exits determines cell’s fate
   If cell killed or lysed  causes more severe disease

Question 30

describe parvovirus viral replication

Answer 30

Infects intestinal crypt epithelial cells
Receptors on basolateral surface
So coming in from circulation, not directly from intestine
M-cell  Peyer’s patch  circulation
Not most direct; prevents contact with protective mechanism, tight junctions

Question 31

how do non-enveloped viruses attach to cells

Answer 31

They attach to host cells using a protein coat
(viral coat, capsid, capsomeres)
Usually kill infected cells to release newly formed virus.

Question 32

how do enveloped viruses attach to cells

Answer 32

They attach to host cells using a viral envelope

Usually do not kill infected cells to release newly formed virus.

Question 33

what are the innate host cell defences against viruses

Answer 33

Inflammation

Interferon

Question 34

what are the host cell mediated immunity against viruses

Answer 34

NK and cytotoxic T cells

Antibodies important only for subsequent infections