Pathogens and Hosts

Question 1

What signs/symptoms characterise clinical infection

Answer 1

• inflammation
• pain
• pyrexia
• tachycardia
• rigors
• increased white cell cound
• increased C reactive protein (CRP)

note: infection can be latent or sub-clinical

Question 2

Pathogen

Answer 2

organism that can cause disease

Question 3

Commensal

Answer 3

organism which is part of normal flora (e.g. E.coli in gut, S.aureus in nose, axilla)

Question 4

What is fighting during pathogen/host interactions

Answer 4

host defence (immune system) vs organism pathogenicity

Question 5

Pathogenicity (infectivty and virulence)

Answer 5

Capacity of microorganism to cause an infection
Requirements:
* infectivity; ability to becoem established
* virulence; ability to cause harmful effects once established

Question 6

Infectivity

Answer 6

Ability to become established on or within a host
Needs:
* Attachment; E.Coli
* Acid resistance; helicobacter pylori

Question 7

Virulence

Answer 7

Capacity to cause harmful effects (disease) once established
Conferred by virulence factors: genetically determined microbial components:
* Invasivness
* Toxin Production
* Evasion of immune system by microorganism

Specific to strains, not species

Question 8

Invasiveness

give example and what it does

Answer 8

Streptococcus pyogenes (Group A streptococci)
* Necrotising fasciitis
* Cellulitis
* CT breakdown (through enzymes/toxins)
* Fibrinolysis

Question 9

Toxins

Answer 9

• Exotoxins are released extracellularly by the microorganism
• Enterotoxins are exotoxins which act on the GI tract
• Endotoxins is structurally part of the G-ve cell wall

Question 10

Explain the Exotoxin: tetanus

Answer 10

• Clostridium.tetani
• Infection of dirty wounds
  * Toxin production: binds to nerve synapses, inhibits release of inhibitory neurotransmitters
• Death caused by respiratory paralysis
• Treatment by debridement, antibiotics and antitoxin

Question 11

Explain the enterotoxin: cholera

Answer 11

• Toxin affecting the intestines (e.g. cholera)
• Vibrio cholerae (colonises small intestine)
• Enterotoxin production: Inc cAMP levels: (inhibits uptake of Na+ and Cl- ions, stimulates secretion of Cl- and HCO3- ions. Passive, large outflow of H2O from gut.
• Causes death by dehydration
• Treated by rehydration

Question 12

Superantigens

Answer 12

• certain exotocins of s.pyogenes and s.aureus
• able to stimulate division of T cells in absence of specific antigen
• Overwhelming cytokine production causes “toxic shock”

Question 13

Endotoxin

Answer 13

• Componet fo G-ve bacterial cell wall: LPS: Lipid A, Oligosaccharide core, spicific polysacchariide chain
• e.coli and other G-ve bacilli
• Induces severe uncontrolled host response: cytokine production, fever/rigors/hypotension/tachycardia/collapse

Question 14

what form of MRSA is easier to treat

Answer 14

community required MRSA as opposed to hospital required MRSA

Question 15

bacillus anthracis

Answer 15

human infections associated with exposure to infected animals or contaminated animal products
Can often be cutaneous and is rarely fatal with treatment

Question 16

what are pathogenic bacteria

Answer 16

those capable of causing disease

Question 16

what are pathogenic bacteria

Answer 16

those capable of causing disease

Question 17

Requirements of pathogenicity

2

Answer 17

infectivity and virulence

Question 18

What is virulence conferred by

Answer 18

invasiveness, toxin production and immune evasion

Question 19

What can harmful effects from bacterial infection be caused by

2 things

Answer 19

• The bacterium
• the host response

often both

Question 20

Virus pathogenic mechanisms

3

Answer 20

• Cell destruction following virus infection
• Virus-induced changes to cellular gene expression (e.g. tumor viruses)
• Immonopathogenic disease (e.g. Influenza A)

Question 21

Sites of viral entry

Answer 21

• Conjunctiva
• Capillary
• Skin
• Respiratory tract
• Alimentary tract
• Urinogenital tract

Question 22

What is the case with the majority of viral infections

Answer 22

Most is unarrparant (either dormant or infection doesn’t show) - like iceberg: only small portion shows

Question 23

4 different types of viral infections

name and breifly describe each

Answer 23

• Acute infection: arise and then goes away
• Latent infection: arises, lies dormant, (stimulus) arises again
• Chronic infection: arises, small dec but remains
• Tumor virus infection: small inc, stable, suddenly shoots up in late diesease stage

Question 24

Examples of acute viral infections

Answer 24

* Influenza A -respiratory infection * Enterovirus - enteric (GI) and neurological infections

Question 25

Summarise process of acute virus infection

Answer 25

* Viral infection * Multiplies and inc exponentially * Reaches peak (symptoms worst) * Host immune system activated and begins to fight back * host develped enough antibodies, and viral numbers dec * Reduce to 0

Question 26

2 features of acute virus infections

Answer 26

Localised to **specific site** of body (e.g. infulenza in resp. tract) Development of **viraemia** with widespread infection of tissues

Question 27

Explain Influenza A virus infection

Answer 27

* Virus infects cells of respiratory tract * Destruction of respiratory epithelium: (secondary bacterial infections) * **Altered cytokine expressio**n leading to fever

Question 28

Explain Influenza A virus infection

Answer 28

* Virus infects cells of respiratory tract * Destruction of respiratory epithelium: (secondary bacterial infections) * **Altered cytokine expressio**n leading to fever

Question 29

Explain Influenza A virus infection

Answer 29

* Virus infects cells of respiratory tract * Destruction of respiratory epithelium: (secondary bacterial infections) * **Altered cytokine expressio**n leading to fever

Question 30

How are novel influenza viruses generated? | 2 mechanisms

Answer 30

* Antigenic **drift**: minor changes (natural mutations) in genes of virus occur gradually over time to generate antigenic varients * Antigenic **shift**: abrupt major changes in virus antigenic structure

Question 31

Give some commone enterovirus infections

Answer 31

* Poliomyelitis (poliovirus) * Aseptic meningitis (many enteroviruses) * Myocarditis (coxsackie B viruses) * Pancreatitis (coxsackie B virus) * Respiratory infections (many enteroviruses)

Question 32

Breifly describbe process of enterovirus infection

Answer 32

* oral ---> GI system (gut) * Viraemia: non-neuronal tissues, neuronal tissues (e.g. CNS) ---> paralysis * Virus also extreted in faeces

Question 33

Where do enteroviruses live/infect initially

Answer 33

The Gut/**intestines** (GI tract)

Question 34

Give example of a latent virus infection

Answer 34

Herpes simplex virus (cold sores = type 1, genital lesions = type 2)

Question 35

Give brief overview of herpes virus infection and latancy

Answer 35

1. Primary infection: * Virus infection of epithelium (e.g. cold sore) * Virus migrates to ganglia * Virus latent in nucleus 2. Reactivation: * Stimulus occurs (e.g. neurological, phycological, immunocompromised) * Virus migrates to epithelium leading to virus replication * Cold sore again * Viral release

Question 36

Give 2 examples of virus-induced tumors

Answer 36

* Papillomaviruses (HPV) - cervical carcinoma * Retroviruses - lymphomas and leukemias

Question 37

Summarise the retrovirus replication cycle

Answer 37

1. Attachment 2. Membrane fusion 3. Uncoating of viral RNA in cytoplasm 4. Reverse transcriptase acts and converts to viral DNA 5. Virus DNA integration into nucleus

Question 38

Summarise retrovirus-induced tumours

Answer 38

* Virus infects cell * Virus nucleic acid, as DNA, integrates into ceullular genome * Virus causes changes in cellular gene expression * Uncontrolled cell multiplication and tumor formation

Question 39

Colonisation

Answer 39

presence of a microorganism on/in a host, with growth and multiplication of the organism, but without interaction between host and organism

Question 40

Latent

Answer 40

the time interval between when an individual or host is infected by a pathogen and when they become infectious, i.e. capable of transmitting

Question 41

Asymptomatic infection

Answer 41

An infection without symptoms

Question 42

Example of tumor causing virus

Answer 42

Human T-lymphotropic virus-1 (HTLV-1): causes abnormal gene expression

Question 43

features of viral pathogenesis

Answer 43

Pathogenesis is the process by which an infection leads to disease. Pathogenic mechanisms of viral disease include: 1. implantation of virus at the portal of entry 2. local replication 3. spread to target organs (disease sites) 4. spread to sites of shedding of virus into the environment.