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Flashcards in Pathogens and Host Deck (59)
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1

What is a pathogen

An organism which can cause disease

2

What is a commensal

An organism which is part of normal flora (e.g. E. Coli in gut, Staph aureus in nose)

3

What are the signs and symptoms of a clinical infection

Inflammation
Pain
Pyrexia
Tachycardia
Rigors
Increased white cell count
Increased C reactive protein (CRP)

4

What is pathogenicity

The capacity of a micro-organism to cause an infection

5

What is pathogenicity dependent on

Infectivity
Virulence

6

What is infectivity

The ability to become established on or within a host

7

What is Virulence

The ability to cause harmful effects (disease) once established

8

How can infectivity occur

Attachment (e.g. E. coli to P-fimbriae using a receptor on uroepithelial cells)
Acid resistance (e.g. Helicobacter pylori using urease makes ammonia from urea)

9

What is virulence determined by

Virulence factors which are genetically determined microbial components such as:
Invasiveness
Toxin production
Evasion of immune system

Virulence factors are specific to the strain not the species

10

How are exotoxins released

Extracellularly by the microorganism

11

What are enterotoxins

Exotoxins which act on the GI tract

12

What structural role do endotoxins have

Part of the Gram negative cell wall

13

Give an example of an exotoxin and its mechanism of action

Tetanus

Clostridium tetani causes an infection in a dirty wound and produces toxins

The toxins bind to nerve synapses and inhibit the release of inhibitory neurotransmitters

It can cause death by respiratory paralysis

Treatment is by debridement, antibiotics and antitoxin

14

Give an example of an enterotoxin and its mechanism of action

Cholera

Vibrio cholerae colonises the small intestine and produces enterotoxins

Toxins:
Increase cAMP levels which inhibit the uptake of Na+ and Cl- ions and stimulates the secretion of Cl- and HCO3- ions
Cause a passive outflow of H2O.

Death is caused by dehydration
Treatment is rehydration

15

What is the structure of a endotoxin

Lipid A
Oligosaccharide core
Specific polysaccharide chain

16

What do endotoxins induce

A severe uncontrolled host response which causes cytokine production
Fever
Rigors
Hypotension
Tachycardia
Collapse

17

What are the sites of viral entry

Conjunctiva
Arthropod
Capillaries
Skin
Respiratory tract
Alimentary tract
Urinogenital tract

18

Name two acute viral infections

Influenza A virus causing a respiratory infection
Enterovirus causing enteric and neurological infections

19

What is antigenic drift

Minor changes (natural mutations) in the genes of viruses.

It occurs gradually over time to produce antigenic variants

20

What is antigenic shift

Abrupt major changes in the virus antigenic structure

21

Name some examples of enteroviruses

Poliovirus
Aseptic meningitis
Myocarditis
Pancreatitis

22

Describe the features of an enterovirus infection

Infection enters the gut
Causes viraemia in non-neuronal tissues and neuronal tissues
Leads to paralysis
Virus is excreted in faeces

23

What do monocytes in the blood mature into

Tissue macrophages

24

Name some polymorphs

Neutrophils
Eosinophils
Basophils

25

Are lymphocytes phagocytic

No

26

Where do T cells mature

Thymus

27

What type of organisms are resistant to phagocytosis

Capsulate organisms (e.g. Strep pneumoniae)

28

Name an organism resistant to intra-cellular killing

Mycobacterium tuberculosis

29

What are polymorphs

Granulocytes

30

What type of macrophages are there

Fixed
Free