Infections Lecture 1: Aetiology, symptoms and transmission of infection Flashcards
What is an infection?
Colonisation of a host organism by pathogenic organism
What is are the branch of medicines that are focused on fighting diseases called?
Infectious disease mechanism
What are the six stages of infectious disease?
- Acquisition
- Colonisation
- Penetration
- Spread
- Damage
- Resolution
Describe the acquisition step and how infections are initially contracted?
- They can be acquired from endogenous micro-organisms in or on the body (bacteria, fungi, viruses etc)
- Contact with exogenous (transmission) microbes
What are the 5 ways to contact exogenous microbes?
- Direct contact- e.g. STIs
- Inhalation/droplet infection- e.g. cold
- Ingestion/faecal route- e.g. gastroenteritis
- Trauma/inoculation e.g. tetanus, malaria, infected topic dermatitis
- Trans-placenta e.g. congenital toxoplasmosis
Describe the general colonisation step?
- Organism must survive and multiply in the environment
- dependent on pH, temperature, competing endogenous organisms - Some are born with mechanisms to help colonisation
- Mucolytic enzymes to penetrate mucous layers
- Influenza virus adheres to glycoprotein receptors on upper respiratory tract mucosal cells
What do bacteria seldom lone cells usually form? And what do they do?
- Usually form complex colonies called “Biofilms”
- Acts as a slimy protective outer layer- other organisms attach to the biofilm
- More difficult to treat than isolated bacteria
Describe the purpose of the general penetration step?
To invade the organism must breach the surface barrier such as skin and mucous membrane
How does the upper respiratory tract deal with foreign particle exposure?
Muco-cillary clearance and cough reflex protects against particulate exposure
Where are the three main areas where cells can penetrate?
- GI tract
- organisms can damage the surface by releasing toxins - Crossing the placenta
- Rubella, syphillis - Cell penetration
- Viruses enter some bacteria and enter host cells via penetration
What are the three main ways infections can spread?
- Along tissue planes
- Extension of colony into surrounding area
- Via vasculature/ lymph (effective rapid spread)
What is the first line of defence against an infection spreading?
Non specific
1. Intact skin and mucous membranes
Body defence
- Sweat (pH)
- Mucous traps bugs
- Anti-bacterial secretions e.g. stomach acid
- Lysozyme in tears
What is the second line of defence against an infection spreading?
Non specific
1. Phagocytosis
Body defence:
1. Phagocytic cells in blood (monocytes, neutrophils)
- Tissues and lungs (macrophages) engulf and destroy micro-organisms
What is the third line of defence against an infection spreading?
Non specific:
1. Inflammation
Body defence:
1. Alongside phagocytic cells they increase at local site and body tries to limit the spread of the organism by forming clot
Describe the mechanical damage infections can do?
Mechanical damage from bulk effects- bacteria and biofilm can obstruct a hollow organ- cystic fibrosis
Describe the toxin damages infections can do?
- Exotoxins produced inside a bacteria (G+ve and -ve) and diffuse out
- Clostridium tetani neurotoxin- tetanus- very toxic
- Endotoxins are LPS protein based complexes mainly in cell wall G-ve bacteria
Describe the damage the altered function of host cell can do?
- Can affect how the cell functions overall in the tissue or organ (common with viruses)
- Can occur as the body tries to combat infection
Describe the damage the host response can have?
- The host damages itself through response to the infection
2. This is usually an inflammatory response which includes swelling, pus, scarring and necrosis
What is a pathogen?
Ability of an organism to cause a disease
What is virulence
Degree of pathogenicity of an organism (ability to cause disease)
What is Attenuation?
Reduction in the virulence (ability to cause disease) of a pathogen
What is Exaltation?
Increase in virulence (ability to cause disease)
Describe the what resolution is in terms of infections? And give examples with HIV and herpes?
- Organism is gone and everything is back to normal
- HIV- you can have a long time with no symptoms, still in the body until it gets worse and immune system cannot take it and it shows
- Herpes- they can flare up and become blisters again
Describe what chemotherapy means?
The use of synthetic chemical to destroy infective agents
Describe the three classes of biochemical reaction that are potential targets for chemotherapy?
Class 1: (poor targets)
- Utilises glucose and other carbon sources to produce ATP and other carbon compounds
Class 2: - Pathway uses energy and class I compounds to make small molecules (e.g. amino acids and nucleotides)
Class 3:
- Pathways convert small molecules into macromolecules like proteins, nucleic acids and peptidoglycan
Give examples of how class 2 reactions are used as targets?
- Folate synthesis is inhibited by sulfonamides
- The utilisation of the folate is inhibited by folate antagonists- e.g. trimethoprim (bacteria) and methotrexate (cancer cells)
- Pyrimidine and purine analogues (e.g. mercaptopurine) for cancer
Give examples of how class 3 reactions are used as targets?
- Beta lactam antibiotics can selectively inhibit bacterial peptidoglycan
- Antibiotics can selectively be inhibit the bacterial protein synthesis stage
- Prevention of tRNA binding (tetracyclines)
- Misreading of mRNA (aminoglycosides)
- Inhibit transpeptidation (chloramphenicol) - Nucleic acid synthesis is impaired by altering base pairing of DNA template (antiviral vidarabine)
- inhibits the DNA polymerase (aciclovir)
- inhibiting DNA gyrase
