Transmission of infectious disease Flashcards
host-microbe interactions
- dynamic give and take between host and microbes
- can range from benign to serious causing disease
human microbiota
- mutualistic relationship
- the microbial population associated with the human body
- human provides nutrients
- promotes immune system maturation
- role of opportunistic pathogens; compete with bad pathogens for real estate; keep in check
tropism
preference for a specific host or tissue
dysbiosis
- disruption of microbiota
- ex. antibiotics can kill good bacteria as well
pathogenicity
ability of a microbe to cause disease
virulence
degree of extent of disease that a pathogen causes
virulence factors
ways pathogens overcome host defenses
ways to invade the immune system:
- toxins
- adhesion factors
- nutrient acquisition
- invasion strategies
attenuated
pathogen is still infectious but does not cause disease
- different for immunocompromised hosts
- attenuation is advantageous because virulence factors use energy to produce
infectious dose (ID50)
the number of bacterial cells or viral particles needed ti establish an infection in 50% of susceptible hosts
lethal dose (LD50)
the amount of toxin needed to kill 50% of untreated affected hosts
toxins
- molecules that generate adverse host effects in a low concentration
- can be tougher to destroy than the originating organism
toxigenic organisms
organisms that produce/generate toxins
toxemia
toxin in bloodstream
endotoxin
- released by gram negative bacteria when the cell is destroyed
- can lead to septic shock and death
- not readily neutralized
- no effective vaccines or therapies
exotoxins
- toxic soluble proteins made by gram negative and gram positive bacteria
- released by the cell into the envrionment
type 1 exotoxins
- membrane acting
- dont enter the host cells
type 2 exotoxins
- damage host membranes
- creates holes in membranes that causes cell to leak and die
type 3 exotoxins
- intracellular AB toxins
- binding portion B binds to plasma membrane
- toxin enters cell by endocytosis
- active portion A enters the host cell and exerts an effect
five steps to infection
- pathogen enters host
- pathogen adheres to host tissues
- pathogen must invade tissues and obtain nutrients
- pathogen must evade host immune defenses in order to replicate
- pathogen must be transmitted to a new host
portal of entry
anywhere you have an opening to the environment; a potential route of infection
adhesins
- allow pathogen to stick to surface of host cells (specifically or nonspecifically)
- make ideal vaccine targets
biofilms
- bacteria growing as a community on a surface
- 60-80% of human infections originate from them
- from implanted devices
- ex. dental plaques
- often change in virulence factor expression
quorum sensing
biofilms are able to communicate via molecular signals that help them become more virulent; can have an adverse reaction to the host
invasins
- allow pathogens to invade host tissues by breaking cell junctions or altering host cytoskeleton
- often have a motility feature
how to pathogen obtain nutrients
siderophores
what are siderophores
iron binding complexes that find a human “lock-box” of iron and steal it for the bacterial cell for food and growth
cytopathic effect
damage or kill host cells; not the cause of all damage
how may pathogens hide from host defenses
- there may be intracellular pathogens
- latency (ability to survive inside a host)
- antigen masking, mimicry, variation
antigen masking
pathogen covers itself in host factors to avoid immune detection
antigen mimicry
pathogens antigens resemble host molecules, helping it evade immune responses
antigen variation
pathogen switches its antigens, thwarting the mounting immune response
how may a pathogen undermine a host immune system
- interfere with phagocytosis
- immune suppression
ways to interfere with phagocytosis
- releasing toxins that kill phagocytes
- avoiding phagocytosis with a capsule
- blocking fusion of lysosome with phagosome
- escaping phagosome and living in a phagocytic cell
- adapting to harsh phagolysosome environment or neutralizing hydrolytic enzymes
biosafety level (BSL)
categorized based on: level of infectivity, extent of disease caused and mortality rate, mode of transmission, availability of preventions/treatments for disease
BSL 1 and 2
- well characterized
- rarely causes disease in healthy people
- human body tissues or fluids
BSL 3
- serious or lethal human disease
- often airborne, may be treatable
BSL 4
- “exotic” pathogens
- extremely dangerous
universal precautions
guidelines applied when dealing with patients suspected or known to have bloodborne pathogen
- originated with HIV epidemic
standard precautions
all patients treated as potential source of bloodborne or other infectious agents
