Host-Pathogen Interactions Flashcards
what are Koch’s postulates?
pathogen is present in diseases and not healthy hosts
pathogen isolated from diseased host and grown in culture
cultured pathogen causes the same disease in experimental host
same pathogen re-isolated from experimental host
what is the relevance of Koch’s postulates?
logical proof that microbe causes disease
what influences host-pathogen interactions?
pathogen
host
environmental factors
what are the six steps in the the life cycle of a pathogen?
transmission
exposure
attachment and colonization
invasion and dissemination
multiplication
shedding
what are the modes of transmission?
horizontal and vertical
what is vertical transmission?
infection of the next generation
what is horizontal transmission?
infection between individuals
what are some routes of exposure?
aerosol
direct contact
inoculation usually from body fluids from diseased
carrier host
reservoir host
vector
fomite
contaminated environment
what does pathogen attachment and colonization often require?
specific molecular interactions
what is invasion and what does it require?
enters cells or tissues
often requires virulence factors
what is dissemination?
spread by blood or lymph
what does multiplication contribute to?
ability of pathogen to shed and infect host
what is shedding usually in?
body fluids: exudates, secretions, excretions, blood, urine, feces
typically, secretions at affected body site are increased
is the disease site usually linked to shedding and transmission?
yes- rule of thumb
what are some shedding exceptions to the rule of thumb?
central nervous system infection: secondary sites (saliva, respiratory, gastrointestinal tract, urinary, blood)
blood: vector borne
what are some issues with Koch’s postulate on pathogen is present in every case of the disease?
multiple pathogens can cause same clinical disease
one pathogen may not cause disease in all hosts
what are some issues with Koch’s postulate on isolating and growing the pathogen in culture?
unable to cultivate
more than one microbe is involved
what is an issue with Koch’s postulate on infecting and inducing disease in healthy animals with the cultured microbe?
animal models may not exist or pay be impractical or the disease is different
what are the limitations of Koch’s postulates?
host-pathogen interactions more complex than single microbe/single disease
outcomes influenced by pathogen, host, and environmental factors
what are some exceptions to Koch’s postulates?
disease caused by multiple organisms (tuberculosis)
asymptomatic carriers (salmonella)
diseases due to organisms we cannot cultivate (or toxins)
requires environmental trigger
what are some disease-causing organisms that we cannot cultivate?
Cryptosporidium spp
M. leprae
how can we overcome the limitation to Koch for uncultivable pathogens/agents?
polymerase chain reaction
what is one pathogen transmitted vertically?
Toxoplasma gondii
how can we overcome the limitations to Koch’s postulates?
polymerase chain reaction for identifying those that will not grow
manipulate virulence factors experimentally (gene deletion and transfer)
