Mechanisms of Pathogenesis Flashcards
1. Know what a pathogen is, difference between pathogenicity and virulence, and two major ways we classify pathogens 2. Know the elements of pathogenesis and supporting concepts
Candida Auris and hospitals
Fungus that only causes infection in hospitals
Pathogen
disease-causing agent
What type of organisms can be pathogens
fungi, virus, bacteria, protists, prions
Pathogenicity vs. virulence
Pathogenicity: ability to cause disease (highly pathogenic = able to cause disease easily)
Virulence: Severity of disease (degree of pathology) - how bad is the pathogen
Pathogenicity and virulence of the common cold, Rhinovirus
Pathogenicity = high
Virulence = low
Pathogenicity and virulence of Ebola virus
Pathogenicity = high
Virulence = High
How do we classify pathogens?
Primary pathogen: capable of causing disease in healthy hosts (Rhinovirus)
Opportunisitc pathogens: cause disease in immunocompromised host
What must a pathogen be able to do to be classified as a primary pathogen
must have means to breach immune system defenses (since it affects healthy hosts)
* e.g. Mycobacterium tuberculosis - replicates and destroys macrophages
What causes a person to be immunocompromised
- Presence of other diseases (HIV/AIDS)
- Genetic defects in immunity
- Autoimmune disorders
- Induction by drugs (e.g. for organ transplant - take immunosupressants)
- Extremes in age
- Lack of proper nutrition
Most fungal pathogens of humans are
opportunistic (Candida)
* many human deaths from fungal diseases occur in AIDS patients
Your friend at the CDC tells you about a new disease-causing bacterium identified. Healthy people are easily getting the disease, and the bacterium has clear adaptations to infect human cells. Not much damaged is caused by the disease however. How would you classify this type of pathogen
Primary pathogen with high pathogenicity and low virulence
Seven elements/mechanisms of pathogenesis
- Maintain a reservoir
- Transport to host
- Invade and colonize host
- Evade host defenses
- Multiply in host
- Damage host
- Leave host
Reservoir
animal or place where a pathogen can be found before or after an infection
* source of infection
* may be necessary for pathogen survival
Example of the reservoir and vector for Yersinia Pestis (cause of the plague)
- Rats
- Fleas
significance of smallpox virus and reservoirs
Lacks a reservoir other than humans
* Why eradication was possible
What makes it very difficult to fully eradicate a virus
whether or not it has a reservoir
Common modes of transport for pathogens
- Via other animals - can be a vector or a zoonotic diseases
- Sexual transmission
- Drinking contaminated water (water-born pathogens) - fecal-oral route
* e.g. Vibrio cholerae - Air-borne pathogens (Rhinovirus)
What pathogen causes the sexuallly-transmitted disease Syphilis
Treponema pallidum
Rarer form of pathogen transmission
Would-related pathogens
examples of wound-related pathogen
- Clostridium tetani - causes tetanus
- Staphylococcus areus - causes impetigo
Main mechanism of a pathogen to invade and colonize a host
Attachment: adhesins are microbial factors that promote attachment to a host surface
Mechanisms of evading a host
- Don’t be recognized
- Resist phagocytosis
- Survive (persist) in phagocytic cells/organelles
- Destroy antibodies
What pathogen is known for being good at evading the host by not being recognized
Borrelia burgdorferi - parasite that causes of Lyme Disease
* Decreases surface proteins recognized by host
* Reside in biofilm
How can pathogens resist phagocytosis
Capsule (polysaccharide layer) prevent phagocytosis
two examples of pathogens that can survive inside phagocytic cells/organelles
- Rickettsia spp.
- Mycobacterium tuberculosis
How does the pathogen Niesseria gonorrhoeae avoid antibodies
ImmunoglobulinA (IgA) proteases break down IgA in host
Where do pathogens multiply in the host
find the place in the body where they grow the best
* salmonella typhimurium = the intensines
* mycobacterium leprae = nerve cells in the appendages
How is a host damaged during pathogenesis
- trigger exaggerated immune response
- Toxins
example of an exaggerated immune response with mycobacterium tuberculosis
granulomas - many immue cells aggreate to “wall of infections”
* pathogen get a free hide out within to grow and mutliply
Exotoxins
soluble proteins released outside the cell
Clostridium tetani
- anaerobic soil Firmicute bacteria
- Causes “lockjaw”
What does Clostridium tetani release that causes lockjaw
Secretes an exotoxin (neurotoxin): tetanospasmin
* causes muscle spasms, can tear muscle fiber
* Lethal dose of tetanospasmin for adult = 175 ng
Endotoxins
released only when cell lyses eliciting immune response
* usually outer membrane lipopolysaccharides
Exotoxins:
a) are secreted by gram-positive bacteria only
b) primarily contain glycolipids
c) are protein toxins made by gram-positive and gram-negative bacteria
d) serve as adhesins for muscosal pathogens
e) contain lipid A
are protein toxins made by gram-positive and gram-negative bacteria
mechanisms of leaving the host
- sexual contact
- vertical transmission (parent to offspring)
- Feces (Fecal-oral route)
- Coughing
- Vector-borne
