Pathogens and Host

Question 1

What is a pathogen

Answer 1

An organism which can cause disease

Question 2

What is a commensal

Answer 2

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

Question 3

What are the signs and symptoms of a clinical infection

Answer 3

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

Question 4

What is pathogenicity

Answer 4

The capacity of a micro-organism to cause an infection

Question 5

What is pathogenicity dependent on

Answer 5

Infectivity

Virulence

Question 6

What is infectivity

Answer 6

The ability to become established on or within a host

Question 7

What is Virulence

Answer 7

The ability to cause harmful effects (disease) once established

Question 8

How can infectivity occur

Answer 8

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)

Question 9

What is virulence determined by

Answer 9

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

Question 10

How are exotoxins released

Answer 10

Extracellularly by the microorganism

Question 11

What are enterotoxins

Answer 11

Exotoxins which act on the GI tract

Question 12

What structural role do endotoxins have

Answer 12

Part of the Gram negative cell wall

Question 13

Give an example of an exotoxin and its mechanism of action

Answer 13

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

Question 14

Give an example of an enterotoxin and its mechanism of action

Answer 14

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

Question 15

What is the structure of a endotoxin

Answer 15

Lipid A
Oligosaccharide core
Specific polysaccharide chain

Question 16

What do endotoxins induce

Answer 16

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

Question 17

What are the sites of viral entry

Answer 17

Conjunctiva
Arthropod
Capillaries
Skin
Respiratory tract
Alimentary tract
Urinogenital tract

Question 18

Name two acute viral infections

Answer 18

Influenza A virus causing a respiratory infection

Enterovirus causing enteric and neurological infections

Question 19

What is antigenic drift

Answer 19

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

It occurs gradually over time to produce antigenic variants

Question 20

What is antigenic shift

Answer 20

Abrupt major changes in the virus antigenic structure

Question 21

Name some examples of enteroviruses

Answer 21

Poliovirus
Aseptic meningitis
Myocarditis
Pancreatitis

Question 22

Describe the features of an enterovirus infection

Answer 22

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

Question 23

What do monocytes in the blood mature into

Answer 23

Tissue macrophages

Question 24

Name some polymorphs

Answer 24

Neutrophils
Eosinophils
Basophils

Question 25

Are lymphocytes phagocytic

Answer 25

No

Question 26

Where do T cells mature

Answer 26

Thymus

Question 27

What type of organisms are resistant to phagocytosis

Answer 27

Capsulate organisms (e.g. Strep pneumoniae)

Question 28

Name an organism resistant to intra-cellular killing

Answer 28

Mycobacterium tuberculosis

Question 29

What are polymorphs

Answer 29

Granulocytes

Question 30

What type of macrophages are there

Answer 30

Fixed | Free

Question 31

Where are fixed macrophages found

Answer 31

Liver Spleen Lymph nodes of mononuclear phagocytic system

Question 32

Where are free macrophages found

Answer 32

Tissues

Question 33

What happens in innate immunity

Answer 33

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

Question 34

What does the mononuclear phagocytic system do

Answer 34

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

Question 35

What does IgM do

Answer 35

Produce primary response

Question 36

What does IgG do

Answer 36

Produce secondary response

Question 37

What does IgA do

Answer 37

Form mucosal immunity

Question 38

What does IgE do

Answer 38

Assist in allergy and helminth infection

Question 39

What is Ig

Answer 39

Immunoglobulins which are proteins with antibody activity. There are 5 classes

Question 40

What is a monoclonal antibody

Answer 40

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

Question 41

What type of specificity do polyclonal antibodies have

Answer 41

Multiple specificity

Question 42

State two features of B-lymphocytes

Answer 42

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

Question 43

What is the complement system

Answer 43

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

Question 44

What types of T cells are there

Answer 44

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

Question 45

Why is cell mediated immunity important in infection

Answer 45

It combats intracellular infection

Question 46

What type of infections does cell mediated immunity attack

Answer 46

Most viral infections Fungal infections Intracellular infections

Question 47

In what type of infections does humoral immunity mainly occur

Answer 47

Bacterial

Question 48

Where do humoral infections occur

Answer 48

Extracelluar

Question 49

Describe the process of cell mediated immunity

Answer 49

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

Question 50

What type of tumour can papillomavirus cause

Answer 50

Cervical carincoma

Question 51

What type of tumours can retroviruses cause

Answer 51

Lymphomas | Leukaemias

Question 52

How can a retrovirus induce tumours

Answer 52

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

Question 53

Where are acute viral infections localised

Answer 53

Specific site of the body | Viraemia will be developed with the widespread infection of tissues

Question 54

What is a feature of viral pathogenesis

Answer 54

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

Question 55

Describe acquired immunity

Answer 55

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

Question 56

What is colonisation

Answer 56

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

Question 57

Define latent

Answer 57

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

Question 58

Define infection

Answer 58

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

Question 59

Define asymptomatic infection

Answer 59

An infection without symptoms