Establishment of Bacterial & Fungal Infections (2)

Question 1

What is a pathogen?

Answer 1

an organism that causes disease

Question 2

What is virulence?

Answer 2

relative measure of pathogenicity

Question 3

What is ID50?

Answer 3

the number of bacteria needed to cause an infection in 50% of exposed animals
ID50 of 100 bacteria is more virulent than ID50 of 1000

Question 4

What is LD50?

Answer 4

lethal dose

the number of bacteria needed to kill in 50% of exposed animals

Question 5

What is MLD?

Answer 5

minimum lethal dose

Question 6

Why do some animals develop severe disease while others do not?

Answer 6

differences in susceptibilities of individual animals

differences in the immune statuses of hosts

differences in breed susceptibilities

Question 7

What is infection?

Answer 7

presence and replication of obligate pathogen within a host

implies obvious disease or capability of causing disease

Question 8

What is an apparent infection?

Answer 8

infection with overt (obvious) disease

acute: short time course; outcome may be death, recovery, or progression to chronic infection

chronic: prolonged time course

Question 9

What is an inapparent infection?

Answer 9

infection without the presence of overt disease

generally results in colonization

Question 10

What is colonization?

Answer 10

presence of an organism without clinical or subclinical disease; however, the organism is replicating

characteristic of inapparent infection

Question 11

What is a carrier infection?

Answer 11

persistent infection with a pathogen that may have previously caused disease

may later progress to an apparent infection

Question 12

What are events in establishment of infection?

Answer 12

encounter - microorganism mees host

entry - microorganism and/or its toxin enters the host body

multiplication and spread - microorganism and/or toxins multiply/spread inside the host

damage - microorganism or host’s immune response can damage the host

Question 13

What happens during initial encounter?

Answer 13

begins at birth

1. challenge with exogenous organisms: 3 possible outcomes
   most common: do not gain entry OR are rapidly eliminated
   less: colonize to form normal flora
2. all neonates receive immunologic protection at birth

Question 14

In calves, some can get enterotoxigenic E. coli due to failure of passive transfer of IgG because they have ______ that allow the organisms to bind

Answer 14

receptors in intestine

Question 15

Later encounters have what two types?

Answer 15

exogenous
endogenous

Question 16

What does exogenous mean?

Answer 16

obtained from an external source

like food-borne salmonella

Question 17

What is endogenous?

Answer 17

due to normal flora that is present in or on the host body

pseudomonas aeruginosa infectado in immunosuppressed patients

Question 18

What are the types of entry?

Answer 18

ingress
penetration

Question 19

What is ingress?

Answer 19

pathogen enters without crossing epithelial barrier

inhalation, ingestion, infection of mucus membranes

Question 20

What is penetration?

Answer 20

pathogen enters by penetrating deeper into tissues

Question 21

What is inhalation?

Answer 21

protection by constitutive host defenses

type of ingress

Question 22

What is ingestion?

Answer 22

role of normal flora

type of ingress

Question 23

What is penetration - pathogen dependent?

Answer 23

specific bacterial structures bind to receptors and facilitate penetration

• these structures are considered virulence factors as they contribute to the virulence of the pathogen

Question 24

What is penetration - pathogen independent?

Answer 24

vector-borne transmission, catheters, blood transfusions

Question 25

What is inoculum size?

Answer 25

prime determinant in outcome of exposure

Question 26

T/F: Even organisms of low virulence can cause disease in large enough numbers

Answer 26

TRUE

Question 27

What is the incubation period?

Answer 27

time between exposure and onset of disease

during this time, bacteria are multiplying to get to large enough numbers to cause disease`

Question 28

What determines multiplication and spread?

Answer 28

Question 29

What are the 3 ways microbes damage the host?

Answer 29

release of endotoxin
production of exotoxin
damaging host response - inflammation, immune escape, immunopathology

Question 30

What is damage by endotoxin?

Answer 30

Question 31

Damage by endotoxin is by gram-[positive/negative/noth] bacteria

Answer 31

both

have very specific and often different actions

most are encoded by plasmids of bacteriophages