Spread/transmission of infectious disease Flashcards
what is virulence and infectivity
virulence- Ability to cause host cell damage
Infectivity- Ability to infect and colonize host
inverses of eachother
Measureing Virulence:
what is LD50 and ID50
LD50- the # of microorganisms needed to kill half of hosts (lower the more deadly)
ID50- the # of microorganisms needed to cause infection in half exposed
What are the 4 virulence factors
- adherence ability
- Evasiveness
- Invasiveness
- production of toxins
What is invasiveness and what do less and higly invassive organisms cause
ability to spread within the host (aided by invasins)
Less invasive organisms cause localized lesion
highly invasive organisms cause generalized infection
What is the function of 1) hyaluronidase + collagenase + 2) coagulase + kinase as invasins
1) break down collegen layer of epithelial cells so it can invade deeper
2) coagulase will create clot so it can surround and hide microorganism, kinase will break down clot after in the blood stream
What are mechanisms of evasiveness
- tolerence to barriers
- blocking attachment with phagocyte
- Block phagocyte opsonins
- blocking fusion with phagocyte
- escaping phagocyte cytoplasm
- producing bacterial antioxidents
- Prod of toxins that kill phagocytes
- Prod proteases that break down antibodies
- use latency
- opa proteins inhibit t helper cells
- surface antigens
- Tegument (outer body covering)
what is an exotoxin vs an endotoxin
exotoxin- secreted by bacteria
endotoxin- a part of the cell wall of gram negative bacteria. Will release upon lysis of cell
what do hyaluronidase and collegenase exotoxins do
hyaluronidase- degredes hyaluronan found in layers of epidermis that connects cells
collagenase- degrades collagen bw endothelial cells allowing bac to enter bloodstream
What do alpha toxin exotoxins do
creates pores in cell membrane causing hemolysis and tissue damage
what does diptheria toxin do
inhibits cell pro synthesis and kills susceptible cells
what does cholera toxin do
over produces cAMP leading to CFTR to eflux ions (and water) out of cells
What does botulinum toxin do
inhibits release of aCH, stopping mm contraction
What does tetanus toxin do
motor neurons will be hyperexcitable because inhibatory neurons are stopped.
Shows as highly active mm spasms
What is the effect of endotoxins
all show the same s+s
- fever
- mm proteolysis
- uncontrolled intravascular coaulation
- shock
2 ways in which bacteria cause tissue damaeg
- Inflammatory rxns due to extra/intracellular multiplication
- Tissue damage due to toxins
ways in which fungi cause tissue damage (zymosan)
Enzymes and metabolic by products cause tissue damage
zymosan- ligand found on surface of fungi (endotoxic effects)
How to parasites cause tissue damage (4)
- mechanical obstruction
- competition for host resources
- Proteases (secretion of enzymes)
- Immunologic rxns
Why do sometimes ppl w antibiotics feel worse right after taking them
will kill gram neg bac and they will release endo toxins
What is the chain of infection steps (6)
- infectious agent
- resevoir
- way out of body
- method of transmission
- person at risk
- way into body
What are kochs postilates
- pathogen must be found in every case of disease
- Pathogen can be isolated + grown in pure culture
- must cause same disease when put into healthy subject
- pathogen can be reisolated from new host
limitations to kochs postulates
- pathogens can be isod from pts not showing symp
- Some pathogens cant be cultivated on media
- exposure to pathogens dont always cause disease
what is a nosocomial infection
aquired while in healthcare facilities
