Pathogenesis of Infectious Diseases

Question 1

Microbial diseases (infectious diseases) are the result of the interaction between microorganisms (_____, ________, _____) and the host organism.

Answer 1

adhering,penetrating and multiplying

Question 2

what is a microorganism

Answer 2

-organism invisible to the naked eye (viruses, bacteria, fungi and some parasites)
-majority are harmless/useful

Question 3

what is an infection

Answer 3

: Penetration of a microorganism, or a part of it capable of multiplication, into a host organism, producing apparent (= disease) or inapparent (= no disease) changes (clinical manifestations).

Question 4

difference between infection vs colonization

Answer 4

infection causes apparent or inapparent changes whereas colonization does not cause any change at all (e.g colonization of the skin with micrococci)

Question 5

What makes inapparent infections challenging?

Answer 5

there are no obvious symptoms

Question 6

What is contamination?

Answer 6

deposition of microorganisms without multiplication (e.g., contamination of sterile dressings by falling dust containing bacteria; contamination of drinking water with sewage)

Question 7

When do clinical infections occur?

Answer 7

when changes result in functional damage to the infected
host.

Question 8

definition of
clinical infection
sub-clinical infection
no infection

Answer 8

• disease
  -sub-clinical infection
  -no infection

Question 9

how are microorganisms capable of producing clinical or subclinical infection classified?

Answer 9

1. pathogenicity, ability of a microorganism to produce disease; invasiveness + toxigenicity
2. virulence, of a microorganism, within a group, to cause damage resulting in disease (in other words the degree of pathogenicity of a particular microorganism).

Question 10

what are opportunistic pathogens?

Answer 10

rarely cause disease in healthy humans, but often do so in humans whose defense mechanisms have been compromised or breached by, for example, a burn or
instrumentation.

Question 11

define transmissibility? routes of entry?

Answer 11

the transfer of an effective challenge amount from a source to a host

a) Inhalation
b) Ingestion
c) Break in protective barrier
d) Direct deposit

Question 12

define toxigenicity

Answer 12

ability to produce toxins

Question 13

define and describe invasiveness?

Answer 13

Microorganisms overcome their host’s immediate defence mechanisms through their ability to:
- adhere to and persist on body surfaces
- protect themselves against bactericidal substances present in body
fluids
- avoid ingestion and destruction by phagocytes

Question 14

how are bacteria’s able to invade,evade the host

Answer 14

surface structures (pili, fimbriae) - adhere to specific receptors present on body cell
surfaces.
Capsules - usually polysaccharides, protect the microorganisms against leucocytes
Enzymes - that, although not toxic per se, may contribute towards the virulence of the
pathogen that elaborates them such as coagulase and hyaluronidase
coagulase: enzyme accelerating the clotting of plasma; the clot formed around the focus of infection constitutes a barrier against leukocytes and body fluids.
hyaluronidase: enzyme hydrolyses polymerizes hyaluronic acid;liquidys polymer

Question 15

what are toxins? types?

Answer 15

substances produced by bacteria that damage host tissues or upset systems vital to the host
-exotoxin and endotoxin

Question 16

what are exotoxins?

Answer 16

proteins excreted by living bacteria cells, active in small concentrations (botulinum can kill a ,am in a dose of 0.0001) often thermolabile (heat sensitive)

Question 17

what are endotoxins?

Answer 17

liberate when cell disintegrates, specific less potent than exotoxins , produce marked clinical effects pyrexia (fever), mailaics , shock. heat resistant and thermostable.
-harder to destroy due to the increase in temperature.