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Principles of Disease > Pathogens and Host > Flashcards

Pathogens and Host Flashcards

1
Q

What is a pathogen

A

An organism which can cause disease

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2
Q

What is a commensal

A

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

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3
Q

What are the signs and symptoms of a clinical infection

A 
Inflammation
Pain
Pyrexia
Tachycardia
Rigors
Increased white cell count
Increased C reactive protein (CRP)
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4
Q

What is pathogenicity

A

The capacity of a micro-organism to cause an infection

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5
Q

What is pathogenicity dependent on

A

Infectivity

Virulence

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6
Q

What is infectivity

A

The ability to become established on or within a host

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7
Q

What is Virulence

A

The ability to cause harmful effects (disease) once established

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8
Q

How can infectivity occur

A 
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)
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9
Q

What is virulence determined by

A

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

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10
Q

How are exotoxins released

A

Extracellularly by the microorganism

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11
Q

What are enterotoxins

A

Exotoxins which act on the GI tract

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12
Q

What structural role do endotoxins have

A

Part of the Gram negative cell wall

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13
Q

Give an example of an exotoxin and its mechanism of action

A

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

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14
Q

Give an example of an enterotoxin and its mechanism of action

A

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

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15
Q

What is the structure of a endotoxin

A

Lipid A
Oligosaccharide core
Specific polysaccharide chain

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16
Q

What do endotoxins induce

A 
A severe uncontrolled host response which causes cytokine production
Fever
Rigors
Hypotension
Tachycardia
Collapse
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17
Q

What are the sites of viral entry

A 
Conjunctiva
Arthropod
Capillaries
Skin
Respiratory tract
Alimentary tract
Urinogenital tract
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18
Q

Name two acute viral infections

A

Influenza A virus causing a respiratory infection

Enterovirus causing enteric and neurological infections

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19
Q

What is antigenic drift

A

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

It occurs gradually over time to produce antigenic variants

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20
Q

What is antigenic shift

A

Abrupt major changes in the virus antigenic structure

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21
Q

Name some examples of enteroviruses

A

Poliovirus
Aseptic meningitis
Myocarditis
Pancreatitis

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22
Q

Describe the features of an enterovirus infection

A

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

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23
Q

What do monocytes in the blood mature into

A

Tissue macrophages

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24
Q

Name some polymorphs

A

Neutrophils
Eosinophils
Basophils

25
Q

Are lymphocytes phagocytic

A

No

26
Q

Where do T cells mature

A

Thymus

27
Q

What type of organisms are resistant to phagocytosis

A

Capsulate organisms (e.g. Strep pneumoniae)

28
Q

Name an organism resistant to intra-cellular killing

A

Mycobacterium tuberculosis

29
Q

What are polymorphs

A

Granulocytes

30
Q

What type of macrophages are there

A

Fixed

Free

31
Q

Where are fixed macrophages found

A

Liver
Spleen
Lymph nodes
of mononuclear phagocytic system

32
Q

Where are free macrophages found

A

Tissues

33
Q

What happens in innate immunity

A 
Phagocytosis of foreign bodies 
Organism held in phagosome
Fusion with lysosome
Forms phagolysosome
Eventually causes intra-cellular killing
34
Q

What does the mononuclear phagocytic system do

A

Causes the:
Spleen to clear blood
Liver to clear entero-hepatic circulation
Regional lymph nodes to drain peripheral sites

35
Q

What does IgM do

A

Produce primary response

36
Q

What does IgG do

A

Produce secondary response

37
Q

What does IgA do

A

Form mucosal immunity

38
Q

What does IgE do

A

Assist in allergy and helminth infection

39
Q

What is Ig

A

Immunoglobulins which are proteins with antibody activity.

There are 5 classes

40
Q

What is a monoclonal antibody

A

An antibody from one clone of plasma cells which has specificity for a single epitope

41
Q

What type of specificity do polyclonal antibodies have

A

Multiple specificity

42
Q

State two features of B-lymphocytes

A

Can differentiate into plasma cells when they recognise a specific epitope
Require T-cell help

43
Q

What is the complement system

A

A complex cascade of about 20 proteins which is triggered from the combination of an antibody (IgG or IgM) to its specific antigen.

44
Q

What types of T cells are there

A
  • CD4 helper cells
    Th1 used in cell mediated immunity
    Th2 which control B cell antibody response
  • CD8 suppressor ad cytotoxic cells.
45
Q

Why is cell mediated immunity important in infection

A

It combats intracellular infection

46
Q

What type of infections does cell mediated immunity attack

A

Most viral infections
Fungal infections
Intracellular infections

47
Q

In what type of infections does humoral immunity mainly occur

A

Bacterial

48
Q

Where do humoral infections occur

A

Extracelluar

49
Q

Describe the process of cell mediated immunity

A

Causes macrophages to present antigens and stimulate T-cells
This causes cytokine production which control the response
Th1 cells activate macrophages to ingest and kill or contain the pathogen while the cytotoxic T-cells (CD8) kill infected host/foreign cells

50
Q

What type of tumour can papillomavirus cause

A

Cervical carincoma

51
Q

What type of tumours can retroviruses cause

A

Lymphomas

Leukaemias

52
Q

How can a retrovirus induce tumours

A

Retrovirus attaches to the cell
Fusion with the membrane
Uncoating so viral DNA interacts with reverse transcriptase
RNA/DNA hybrid produced
Formation of viral DNA integrated into cellular genome
Change in cellular gene expression
This leads to uncontrolled cell multiplication and tumour formation

53
Q

Where are acute viral infections localised

A

Specific site of the body

Viraemia will be developed with the widespread infection of tissues

54
Q

What is a feature of viral pathogenesis

A

Antibodies neutralise viruses in their viraemic stage to prevent adherence of microorganisms and opsonise capsulate organisms

55
Q

Describe acquired immunity

A

Produces a specific response to the antigen concerned
Creates immunological memory.
Has humoral (antibody) and cell (T cells) mediated response with each organism being a complex mixture of antigens and each antigen normally being a mixture of epitopes

56
Q

What is colonisation

A

The development of a bacterial infection in an individual seen in a positive culture. The individual may have no signs or symptoms but have the potential to infect others

57
Q

Define latent

A

An asymptomatic infection capable of manifesting symptoms under particular circumstances or if activated

58
Q

Define infection

A

invasion and multiplication of an infectious agents in body tissues of the host and may lead to clinical symptoms or local cellular injury because of competition in metabolism, production of toxins, intracellular replication, or antigen antibody response

59
Q

Define asymptomatic infection

A

An infection without symptoms

Principles of Disease (41 decks)

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