Host-Pathogen Interactions

Question 1

what are Koch’s postulates?

Answer 1

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

Question 2

what is the relevance of Koch’s postulates?

Answer 2

logical proof that microbe causes disease

Question 3

what influences host-pathogen interactions?

Answer 3

pathogen
host
environmental factors

Question 4

what are the six steps in the the life cycle of a pathogen?

Answer 4

transmission
exposure
attachment and colonization
invasion and dissemination
multiplication
shedding

Question 5

what are the modes of transmission?

Answer 5

horizontal and vertical

Question 6

what is vertical transmission?

Answer 6

infection of the next generation

Question 7

what is horizontal transmission?

Answer 7

infection between individuals

Question 8

what are some routes of exposure?

Answer 8

aerosol
direct contact
inoculation usually from body fluids from diseased
carrier host
reservoir host
vector
fomite
contaminated environment

Question 9

what does pathogen attachment and colonization often require?

Answer 9

specific molecular interactions

Question 10

what is invasion and what does it require?

Answer 10

enters cells or tissues
often requires virulence factors

Question 11

what is dissemination?

Answer 11

spread by blood or lymph

Question 12

what does multiplication contribute to?

Answer 12

ability of pathogen to shed and infect host

Question 13

what is shedding usually in?

Answer 13

body fluids: exudates, secretions, excretions, blood, urine, feces
typically, secretions at affected body site are increased

Question 14

is the disease site usually linked to shedding and transmission?

Answer 14

yes- rule of thumb

Question 15

what are some shedding exceptions to the rule of thumb?

Answer 15

central nervous system infection: secondary sites (saliva, respiratory, gastrointestinal tract, urinary, blood)
blood: vector borne

Question 16

what are some issues with Koch’s postulate on pathogen is present in every case of the disease?

Answer 16

multiple pathogens can cause same clinical disease
one pathogen may not cause disease in all hosts

Question 17

what are some issues with Koch’s postulate on isolating and growing the pathogen in culture?

Answer 17

unable to cultivate
more than one microbe is involved

Question 18

what is an issue with Koch’s postulate on infecting and inducing disease in healthy animals with the cultured microbe?

Answer 18

animal models may not exist or pay be impractical or the disease is different

Question 19

what are the limitations of Koch’s postulates?

Answer 19

host-pathogen interactions more complex than single microbe/single disease
outcomes influenced by pathogen, host, and environmental factors

Question 20

what are some exceptions to Koch’s postulates?

Answer 20

disease caused by multiple organisms (tuberculosis)
asymptomatic carriers (salmonella)
diseases due to organisms we cannot cultivate (or toxins)
requires environmental trigger

Question 21

what are some disease-causing organisms that we cannot cultivate?

Answer 21

Cryptosporidium spp
M. leprae

Question 22

how can we overcome the limitation to Koch for uncultivable pathogens/agents?

Answer 22

polymerase chain reaction

Question 23

what is one pathogen transmitted vertically?

Answer 23

Toxoplasma gondii

Question 24

how can we overcome the limitations to Koch’s postulates?

Answer 24

polymerase chain reaction for identifying those that will not grow
manipulate virulence factors experimentally (gene deletion and transfer)