Virulence

Question 1

Define virulence:

Answer 1

the ability of a pathogen to cause disease

Question 2

How can virulence be measured/estimated?

Answer 2

By the lethal dose which is the amount of agent it takes to kill 50% of a group of animals in a test group. The more highly virulent the pathogen, the less amount of agent required to kill 50%.

Question 3

Define attenuation:

Answer 3

This is a method of vaccination as the virulence of the pathogen is greatly reduced so can be given as a vaccine

Question 4

What is the difference between toxicity and invasivness in terms of pathogenesis?

Answer 4

Toxicity is when the pathogen produces toxins to inhibit cell function whereas invasiveness is simply the growth of pathogen in host tissue without releasing toxins

Question 5

What is a capsule as a virulence factor?

Answer 5

a polysaccharide coat around the bacterial cell

Question 6

What is a pillus as a virulence factor?

Answer 6

to attach a bacterial cell to specific surfaces or to other cells

Question 7

What causes diptheria and what is it?

Answer 7

Corynebacterium diphtheria
gram +ve,
non motile
club shape

Question 8

What causes whooping cough?

Answer 8

Bordetella pertussis
gram-ve
aerobic cocco bacillus
confined to humans

Question 9

What is the pathogenesis of whooping cough?

Answer 9

attach and replicate on ciliated URT mucosa and produce 3 types of toxins:

a) pertussis exotoxin (released outside the organism)
b) Tracheal cytotoxin
c) invasive adenylate cyclase toxin
- can cause secondary pneumonia

Question 10

What causes cholera?

Answer 10

Vibrio cholera
comma shaped
gram -ve

Question 11

What is the pathogenesis of cholera?

Answer 11

acute infection of GI tract by production of cholera toxin and adenylate cyclase upregulation

Question 12

Give 3 examples of a partially invasive pathogens?

Answer 12

E.coli, influenza and shigellosis

Question 13

What are the 3 examples of non-invasive pathogen diseases?

Answer 13

cholera, diptheria and whooping cough

Question 14

What causes shigelloisis? (blood and puss in diarrhoea)

Answer 14

shigella sonnei for mild infections
shigella flexneri for severe infections
shigella dysenteriae for very severe
gram -ve rods, facultative anaerobes, non spore forming

Question 15

What is the pathogenesis of shigelloisis?

Answer 15

shiga toxin causes partial invasion of membrane

Question 16

Give an example of invasive pathogenic disease:

Answer 16

enteric fever

Question 17

What causes enteric disease (typhoid)?

Answer 17

salmonella enterica - systemic infection causing constipation, fever and has a 3 week duration

Question 18

How is typhoid transmitted?

Answer 18

person to person through contaminated foods and primary infection is through the jejunum or SI

Question 19

What is an example of a disease without bacterial colonisation?

Answer 19

Food poisoning which is the consumption of food containing toxins e.g. botulism, staphylococcus aureus and bacillus cereus

Question 20

What is the pathogenesis of diptheria?

Answer 20

It causes a thick covering (pseudomembrane formed) at the back of the throat leading to difficulty breathing and swallowing so is vaccinated against as a child. 
An AB (activity and binding function) toxin produced by the bacteria causes this damage, inhibiting protein synthesis (EF2)

Question 21

Describe botulism food poisoning:

Answer 21

• ingestion of botulinum toxin produced by clostridium botulinum
• obligate anaerobe
• spore forming
• gram +ve
• heat stable

Question 22

Describe staphylococcus aureus food poisoning:

Answer 22

toxin ingested interacts with gastric mucosa causing enterotoxins, rapid symptoms (caused by creamy foods, custards etc)

Question 23

Describe bacillus cereus food poisoning:

Answer 23

• obligate anaerobe
• spore forming
• 2 disease forms:
  a) emetic toxin - heat stable, short incubation
  b) enterotoxins Nhe and EBL - heat labile, longer incubation and diarrhoea forming
• grows in rice