Host-Pathogen Interactions

Question 1

Examples of host physical and chemical defenses

Answer 1

• skin
• normal flora
• flushing effect (tears, urine)
• GIT (low pH)
• vaginal tract

Question 2

Portals of entry for the parasite

Answer 2

• resp tract (inhalation)
• GIT (ingestion)
• genital tract (sexual transmission)
• skin (abrasions, bites)
• congenital (vertical)
• other (injections)

Question 3

Define a reservoir of infection

Answer 3

• where the infectious agent is normally found and where it may multiply or survive

Question 4

Define a source of infection

Answer 4

May be the patients own flora, animal or environmental source

Question 5

To cause disease a pathogen must:

Answer 5

• gain access to host
• adhere to host tissues
• penetrate or evade host defenses
• damage the host

Question 6

How is disease achieved

Answer 6

• adherence
• colonisation
• invasion

Question 7

Characteristics needed for a pathogen to cause disease

Answer 7

• transmissibility
• survival
• infectivity

Question 8

Types of pathogens

Answer 8

• primary (neisseria meningitidis)

- opportunistic (staph epidermidis)

Question 9

Define pathogenicity

Answer 9

Capacity of an organism to cause disease

Question 10

What determines virulence?

Answer 10

• toxin production (type and amount)
• invasiveness and spread
• immune evasion

Question 11

Define virulence

Answer 11

The disease-causing properties of a strain of pathogen

Question 12

Examples of virulence factors in Strep pyogenes

Answer 12

• streptokinase (dissolution of clots)
• DNAses
• streptolysin O
• erythrogenic toxin

Question 13

What does the M protein do?

Answer 13

• heat and acid resistant
• mediates attachment of bacterium to epi cells
• resists phagocytosis by leukocytes

Question 14

5 groups of potential bacterial contributors to pathogenesis of infectious diseases

Answer 14

• adhesins
• invasins
• impedins
• aggressins
• modulins

Question 15

Define adherence

Answer 15

Attachment to the host by the microbe at portal of entry

Question 16

Describe flagella

Answer 16

• long filaments

- produce motility by rotation

Question 17

Describe fimbriae or pili

Answer 17

• finer, shorter fragments
• responsible for attachment and adhesion
• sex pili for gene transfer

Question 18

Mechanisms to overcome anatomical barriers

Answer 18

• production of tissue-damaging exoenzymes
• parasite-directed endocytosis
• phagocytosis of enteropathogenic bacteria by M cells in intestine

Question 19

Types of spread

Answer 19

• local
• cell-to-cell
• translocation of mac-resistant bacteria to intestine and ingestion by M cells
• lymphogenous or hematogenous generalization

Question 20

Describe the action of a capsule

Answer 20

• usually polysaccharide material
• impairs phagocytosis
• prevents engulfment and destruction by leukocytes

Question 21

Mechanisms for antiphagocytosis

Answer 21

• capsule
• phagocyte toxins
• macs disabled by type iii secretion system
• inhibition of phagosome-lysosome fusion
• inhibition of phagocytic oxidative burst

Question 22

Types of toxins

Answer 22

• exotoxins (secreted by bacteria)

- endotoxins (cell wall)

Question 23

Symptoms of tetanus

Answer 23

• trismus
• neck stiffness
• difficulty swallowing
• rigidity of abdo muscle
• facial muscle spasm
• back muscle spasm
• generalised tetanic seizures

Question 24

Types of exoenzymes

Answer 24

• coagulases
• kinases
• hyaluronidase
• collagenase

Question 25

Mechanisms of immunotolerance

Answer 25

• prenatal infection

- molecular mimicry

Question 26

Describe superantigens

Answer 26

• gram positive exotoxins
• cause polyclonal T cell activation
• massive cytokine release