Disease & Epidemiology

Question 1

Pathogenicity process

Answer 1

virulence (ability to cause disease)
1. Entry: beating the innate host defenses (mucosal membranes are the most common portal of entry for humans) parenteral route: involves broken skin/blood (insect bite)
- portal entry protections: skin and mucous membranes coated with mucin and IgA
2. Adherence: search for a unique niche; requires adhesin + the host cell receptor; sticky pilli bind to mannose and fibronectin; biofilms
3. Invasion: getting into the cell; some bacteria are either obligate or facultative intracellular pathogens; viruses must enter a host cell to replicate
4. Immune Evasion: include the capsule (glycocalyx surrounding the cell) antigenic variation (pathogens can alter the antigen surface), and intracellular growth
5. Injury: toxigenicity (endotoxins/exotoxins); disruption of host cell function; multiplication causing rupture; injury can occur by inflammation or misdirected immune responses

Question 2

Endotoxins

Answer 2

toxins released when bacteria die; generally less harmful because they are not able to as easily enter host cells

Question 3

Exotoxins

Answer 3

toxins produced and released by living bacteria; more harmful

Question 4

Opportunistic infection

Answer 4

infection caused by pathogenic microorganisms that took advantage of the present vulnerable condition of the person such as a weaker immune system or a break in skin integrity
- normal flora can cause disease if they reach sterile sites or if the population of flora is disrupted; E.coli normal in the gut but can cause a UTI; mouth flora can cause dental cavities

Question 5

Parasitic infection

Answer 5

infectious disease transmitted by a parasite

Question 6

Primary infection

Answer 6

infection that occurs in a person by merely acquiring pathogenic microbes via any route of transmission

Question 7

Secondary infection

Answer 7

infection that occurs as a result of the management of previous infection or during the course of another infection

Question 8

Vector transmission

Answer 8

Dengue is a bloodborne virus spread through the bite of a mosquito, an example of this biological transmission

Question 9

Contact transmission

Answer 9

transmission through direct or indirect contact with the pathogen

Question 10

Vehicle transmission

Answer 10

transmission through water or food

Question 11

Droplet transmission

Answer 11

coughing/sneezing, respiratory pathogens that can be transmitted from human to human (cold/flu)

Question 12

Microbial antagonism

Answer 12

exclusionary effect; competition between microbes; normal flora protect the host by competing for nutrients, producing substances harmful to invading microbes; and affecting pH and available oxygen

Question 13

Streptococcus spp

Answer 13

normal host flora in stomach/oral cavity

Question 14

Bacteroides spp, Enterobacter spp, and Klebsiella spp

Answer 14

normal flora found in the colon

Question 15

Lactobacillus acidophilus

Answer 15

GRAM+ bacteria present in the vagina microbiota

Question 16

Corynebacterium spp

Answer 16

GRAM+ rods present in the normal flora of the skin

Question 17

Koch’s Postulate #1

Answer 17

Same pathogen must be present in every case of the disease; infectious organism must not be present in a healthy host

Question 18

Koch’s Postulate #2

Answer 18

Pathogen must be isolated from the diseased host and grown in pure culture

Question 19

Koch’s Postulate #3

Answer 19

Pathogen from pure culture must cause disease when inoculated into a healthy, susceptible lab animal

Question 20

Koch’s Postulate #4

Answer 20

Pathogen must be isolated from the inoculated animal and be shown to be the original organism

Question 21

Exceptions to Koch’s Postulates

Answer 21

• some pathogens can cause several different disease conditions
• some pathogens cause disease only in humans
• some microbes have never been cultured

Question 22

Risk factors for disease severity:

Answer 22

Age, occupation, nutrition, lifestyle (unprotected sex/alcoholism), climate/weather, gender, inherited traits, chemotherapy (depletes WBCs), and pre-existing conditions (like HIV)

Question 23

Bacterial capsules

Answer 23

only found in some bacteria; made of hydrophilic polysaccharide gel; this gel forms a discrete layer in capsules; if gel is amorphous (loose), then it’s called a slime layer
- function to protect the bacteria from the immune system
- Prevents adhesion of the immune cell to the pathogen
- Prevents phagocytosis by binding a host complement regulating protein that is found in the serum (factor H)

Question 24

Factor H

Answer 24

degrades complement proteins as they attach to the bacterial cell surface preventing opsonization

Question 25

Opsonization

Answer 25

coating of a pathogen with complement proteins; allows WBCs to phagocytize the pathogen

Question 26

Iron

Answer 26

Iron is required by bacteria in order to grow; very little free iron in human blood or body fluids since it’s sequestered by iron-binding proteins (transferrin, lactoferrin)

Question 27

Siderophores

Answer 27

secreted by bacteria to compete with host iron-binding proteins; these bind iron more tightly than the host iron-binding proteins; then are transferred into the bacterium (binds to and facilitates uptake of iron)
- Interact with a ligand to bind ferric iron and deliver soluble iron across the cell membrane via ion transport mechanism (secondary active transport) from low to high concentration (requiring energy)

Question 28

How to combat the effect of siderophores?

Answer 28

antibiotic-siderophore conjugate: a mechanism against invading bacteria; conjugate would be imported and the antibiotic would kill the bacterial cell