Epidemiology and Pathogenesis Flashcards
In addition to IDing the microbe, what else must be done to conclude that a microbe causes a particular disease?
ID the strain’s virulence factors and genes for virulence
What does the term Incidence mean in epidemiology?
new cases
What does the term prevalence mean in epidemiology?
total cases
How is endemic disease characterized?
By regional location and periodic outbreaks
How are epidemic and pandemic diseases characterized?
By…
-widespread occurrence (scale is definitive)
-rapid outbreak
What is a reservoir?
Where the disease is when it is not happening (active)
What are disease reservoirs considered?
Sources of ongoing infection/”where pathogens come from”
What are human reservoirs?
ill persons/carriers
What are nonliving reservoirs?
soil, waters air
What are animals and vectors-living character of disease that is not human?
ticks, mosquitos, etc
What is direct contact transmission?
by physical contact with infected person/animal (can be vertical or horizontal)
What is indirect contact transmission?
by contact with a contaminated material (fomite)
What is droplet contact transmission?
contaminated droplets contact membranes (short range)
What is vehicle transmission?
by exposure to contaminated water/air/food (may involve fecal-oral mode and long-distance)
What is vector transmission?
by saliva/feces from an insect/arthropod/animal
What is a nosocomial infection?
An infection that occurs in a healthcare setting when the first stage of immune defenses is bypassed (barrier defenses)
What is pathogenicity?
the ability to cause disease
What is virulence?
the degree of ability to cause disease
True or False:
Virulence factors are not essential for causing disease
False, they are essential for causing disease
Can virulence be quantified?
Yes, depends on the # of microbes (“load”) ID50 and LD50
What is ID50?
How many organisms it takes to infect half the population
What is LD50?
The lethal dose- how many organisms it takes to kill half the population
True or False:
The lower the number of ID50, the more virulent it is.
True
What are cons of virulence factors?
-enables microbe to establish itself in host
-enhances microbes ability to cause disease
What are pros of virulence factors?
-they are often antigenic
-may be used serologically
-may be inactivated by the immune system
What are primary pathogens?
-they cause disease upon infection
-NOT typically associated with host
(ex: influenza)
What are opportunistic pathogens?
-they cause disease under some circumstances
-often members of normal flora
(ex: e.coli)
What are the important cocci gram-positive flora organisms?
-Staph aureus
-Staph epidermis
-Strep pyogenes
-Viridians Strep
What is the important spore forming bacilli gram positive flora organism?
Clostridium
What is the important cocci gram negative flora organism?
Neisseria meningitidis
What are the important bacilli gram negative flora organisms?
E. coli, Bacteroides, Pseudomonas, lactobacilli
What is the important acid-fast flora organism?
mycobacterium
What is the important fungi flora organism?
Candida albicans
True or False:
Flora organisms defend you, but some of them could be opportunistic pathogens
True
True or False:
Disease from opportunistic infections is common in immunocompetent persons
False- it is uncommon in immunocompetent persons
How can opportunistic infection be promoted?
-Immunodeficiency or Immunosuppression
-Flora microbes being “out of place”
-Disturbance of “normal flora balance”
Internal tissues, organs, and body fluids should be what?
Free of ALL microbes (sterile)
What are the transmissions to a Portal of Entry?
-Respiratory Tract (RT) membranes
-Gastrointestinal tract (GIT) membranes
-Genitalurinary tract (GUT) membranes
-Skin (Paraenteral)
Both vertical and Horizontal transmission are appropriate
What is the first step to colonization?
Attachment by…
-Pili
-Virus spikes
-Capsules
-Teichoic acids
-Surface proteins
What does attachment do in colonization?
The specificity determines the host range
What does neutralization do?
Neutralizing antibodies can stop attachment
What is colonization?
-Multiplication and Maintenance
-Primary pathogens are “not in place”
What are barriers to colonization?
-Competition with the normal flora (will defend you to some extent- has squatter rights to some parts of your body)
-Barriers’ defenses:
-bile, stomach acid, skin secretion, competition for iron, etc
After initial colonization, how do you avoid phagocytosis?
by capsules
After initial colonization, how do you avoid antibodies?
-antigenic variation
-acquiring an intracellular lifestyle
What do enzymes that degrade tissue, antibodies, etc do?
Promote further invasion into tissues
NOT TOXINS
How is reduced phagocytosis reached?
Capsule production on surface of bacteria reduces “exposure” to complement proteins
What can antigenic variation be due to?
-many antigen variants in a population
-change of surface antigens over time
What are the outcomes of antigenic variation?
-Immune system evasion
-Possible re-infection (ex: flu, covid)
What is the result of avoiding antibodies?
reduced exposure to the humoral immune response
True or False:
In avoiding antibodies, some intracellular microbes survive within phagocytes, other cells.
True
What are exotoxins?
-external
-secreted proteins
-mostly gram positive
-VERY potent
-Cytotoxic and tissue specific
-Soluble
-Strongly antigenic
-protective antibodies = neutralization
What does heat labile mean?
can make toxoids
True or False:
Exotoxins are not heat labile
False, exotoxins are heat labile
What are two problems presented with exotoxins?
You have an infection occurring, and you have exotoxin affects occurring that have to be treated simultaneously
Where are the exotoxin genes encoded?
plasmid or phage-encoded
What is a super-antigen?
an exotoxin that…
-bind to MHC 11 proteins and presented without antigen processing
-leads to polyclonal T cell stimulation
-excess inflammatory cytokines
What do excess inflammatory cytokines look like?
Low BP -> shock -> multi-organ failure (Toxic Shock Syndrome)
True or False:
The immune system must be highly regulated
True
What do T-helper cells do?
express cytokines that are pro-inflammatory
What are endotoxins?
-LPS
-Gram negative
-not a protein and not secreted
-highly antigenic
-LPS is heat-stable
What are the two problematic components of LPS?
-Lipid A: toxic in bloodstream/membrane
-O antigen (polysaccharide) is antigenic
What does Lipid A do?
-prompts macrophages (immune cell stimulation) to express pro-inflammatory cytokines
-induces fever and shock
-Widespread coagulation
True or false:
Endotoxin genes are bacterial
False, endotoxin genes are chromosomal
True or False:
Endotoxins can’t be denatured
True
Infection may lead to….
shock
How can infection lead to shock?
Decreased perfusion of blood -> decreased tissue oxygen -> multiple organ failure
