pathogens and hosts

Question 1

Describe some of the features of viral pathogenesis?

Answer 1

Can result in:
- Death of cells 
-Changes to gene expression
-Repair of cells.
Can be:
-Acute
-Latent
-Chronic
-Tumour inducing
Depends on:
-Infectivity
-Virulence

Question 2

Define the terms pathogen and commensal.

Answer 2

Pathogen: A microorganism which causes disease
Commensal: A microorganism which is part of the normal flora of the body
Koch’s postulate helps define whether it is a pathogen or a commensal:
-Whether it can survive for many generations outside the body
-whether it is present at all stages of the disease
-whether it causes the same symptoms when inoculated

Question 3

Describe in outline the human defence mechanisms of innate and acquired immunity.

Answer 3

Innate- skin, membranes, mucous
Aquired:
-Phagocytosis
-Antibody+ complex system
-Cell-mediated immunity: when macrophage present antigen triggering T-mediated response.

Question 4

Explain the meaning of the terms colonisation, latent or asymptomatic infection and infection.

Answer 4

Colonisation: microorganism present but is asymptomatic
Infection: microorganism is a pathogen- present and causes disease
Latent: 1st response equal to second in terms of quantity.
-Initial symptoms due to pathogen destroying epithelium.
-Virus then become latent in nuclei
-A stimuli causes the virus to become reactivated
-The virus then continues to destroy the epithelium.
E.g. Herpes simplex

Question 5

Define pathogenicity and describe the concepts of infectivity and virulence

Answer 5

Pathogenicity: The ability of a pathogen to cause infection
Infectivity: The ability of a pathogen to establish itself. Depends on attachment or acid resistance.
Virulence: The ability of the pathogen to cause harm.
It depends on toxin production , invasiveness and evasion of the immune system.

Question 6

Describe the features of pathogenic toxins and their effects

Answer 6

exotoxin- released by microorganism
endotoxin- found in lipopolysaccharide in lipid A in gram negative wall.
enterotoxin- released by microorganism in the gut

Question 7

Describe the sites of viral entry

Answer 7

• skin
• Capillaries
• Respiratory tract
• Alimentary tract
• Urinogenital tract
• Conjunctiva- mucous membrane which covers the front of the eye

Question 8

Describe the features of acute viral infections with the use of examples

Answer 8

Large amount of virus over short period of time.
Initially found in specific site of body but once it moves into the blood can infect many different tissues.
e.g. Influenza A
-Enters through the respiratory tract
-Destroys the respiratory epithelium
-Alters the cytokine expression
Variation of the influenza virus:
-Antigenic shift: An abrupt change in antigenic structure- can be aided by non-human host infection
-Antigenic drift: A gradual change in the gene expression of the virus which can lead to antigenic variation.

Question 9

Describe the features of enterovirus infection with the use of examples

Answer 9

Enters through the Gut.
During Viraemia can move into blood- if it moves to neuronal tissues can lead to paralysis.
It can also be excreted.
e.g. pancreatitis, myocarditis, poliomyelitis

Question 10

Describe how virus can induce tumours with the use of examples

Answer 10

Initial infection- small amount of virus.
Virus is able to reproduce in the body:
-binds to cell membrane
-unfolded in cytoplasm
-retrovirus forms hybrid DNA and RNA
-Viral DNA formed which can be incorporated into the DNA of the cell.
-Leads to uncontrolled cell division

Question 11

examples of commensals

Answer 11

E. coli in the gut

Staph aureus in the nose

Question 12

Examples of pathogens infectivity

Answer 12

E. coli: have P-fibrae which allow it to bind to receptors

Helicobacter Pylori: has Urease which allows it to produce urea from ammonia- acid resistant

Question 13

Example of an exotoxin

Answer 13

Tetanus:

• clostridium tetani
• Dirty wounds
• releases an exotoxin which binds to nerve synapses and prevents the release of INHIBITORY neurotransmitter
• Causes respiratory paralysis

Question 14

Example of an enterotoxin

Answer 14

Cholera:
-vibrio cholera 
-Increases levels of Camp
decreases uptake of Na+ and cl- into the cell 
- increases secretion of Cl- and Hco3-
-massive outflow of H20 into the lumen 
-causes death by dehydration

Question 15

Example of endotoxin

Answer 15

• Released from lipid A IN lipopolysaccharide in gram negative wall of bacteria
• E. coli and Neisseria meningitis
• Severe uncontrolled host response- cytokine production, hypotension, fever..

Question 16

Superantigens

Answer 16

exotoxins of staph aureus and pyogens stimulate T cell division in absence of specific antigen
-high cytokine production can lead to toxic shock

Question 17

virus induced tumours

Answer 17

• Retroviruses can cause lymphomas and leukaemias

- Papillomaviruses can cause cervical carcinomas

Question 18

Provirus

Answer 18

Virus DNA in host nucleus

Question 19

Human T-lymphotrophic virus 1

Answer 19

Transmission via blood from mother to child
Infects T cells
Modifies host cell DNA through tax protein
Responsible for many diseases including lymphomas