PARADIGMS OF INFECTIOUS DISEASE Flashcards
What is the definition of virulence?
The relative ability of a pathogen to cause disease (measure of pathogenicity)
What do pathogens use to enhance their pathogenicity (3)?
- Virulence factors
- Toxicity and invasiveness (can determine whether an infection is local or systemic)
What is the definition of attenuation and how does it occur? (3)
- The decrease or loss of virulence
- Caused by the alteration of favourable growth conditions of an organism, resulting in reduced virulence
- Can occur naturally or can be caused deliberately when producing a vaccine
What is the definition of toxicity (2)?
- The organism releases a toxin, this toxin inhibits host cell function or kills the host cell
- The toxin can travel to different sites - this can lead to systemic infection
How to measure virulence (2)?
- Virulence can be estimated from experimental studies of the LD50 (lethal dose50)
- LD50 is the amount of a agent required to kill 50% of a test group
What is the definition of invasiveness?
- Ability of a pathogen to grow in host tissue at densities that inhibit host function
When a pathogen enters a host, what is it called? Also, how do pathogens spread after entering the host?
- Adherence - entry of the pathogen into the host
- Spreads throughout the host via circulatory or lymphatic systems
Give two examples of anatomical virulence factors of a bacterial cell?
- Capsule - Protects bacterial cell and allows the organism to invade the immune system
- Pili (proteinaceous structures)- Allows attachment of bacteria to host cells and prevents organisms from being washed away
What is the definition of a non-invasive pathogen (4)?
- Involves viable bacteria1 but the bacteria doesn’t penetrate the epithelial layer2
- Localised at point of entry3 or mediated by exotoxins4
What are some examples of non-invasive pathogens? (3)
- Diptheria
- Whooping cough (pertussis)
- Cholera
What’s the causative agent of Diptheria?
Corynebacterium diphtheriae - inhaled
What’s the morphology of Diptheria? (3)
- Gram-positive
- Non-motile
- Clubbed morphology
What’s the clinical presentation of Diptheria? (3)
- Pseudomembrane (throat)
- Difficulty swallowing
- Systemic effects – heart complications, coma, death
What’s the pathogenesis (how can it cause disease) of Diptheria?
Production of AB toxin inhibits EF2 which prevents protein synthesis and kills the cell
What’s the causative agent of Whooping cough (pertussis)?
Bordetella pertussis
What’s the morphology of Whooping cough (pertussis)? (3)
- Gram-negative
- Aerobic cocco-bacillus
- Confined to humans
What’s the clinical presentation of Whooping cough (pertussis)? (3)
- Paroxysms of cough (whoop)
- CNS effects
- Secondary pneumonia
What is the pathogenesis (how it cause disease) of Whooping cough (pertussis)? (4)
- Attachment and replication on ciliated URT mucosa
- Produces pertussis exotoxin, tracheal cytotoxin and invasive adenylate cyclase toxin
What’s the causative agent of Cholera?
Vibrio cholera
What’s the morphology of the causative agent of Cholera? (2)
- Comma shaped
- Gram-negative
What’s the clinical presentation of Cholera?
- Infects small intestine causing rice water stools
What is the pathogenesis (how it cause disease) of Cholera?(4)
Cholera toxin1 increases adenylate cyclase activity2 which causes excess salt and water movement into the lumen of the small intestine3,death by dehydration4
What is meant by a partially-invasive pathogen?(3)
Invade epithelial layer1 but don’t penetrate deeper tissue2. They invade at primary site of infection only3
Give an example of a disease caused by a partially invasive pathogen and name it’s causative agent(s)? (3)
Shigellosis
Causative agent:
- Shigella sonnei – mild infections
- Shigella flexneri – severe infections
- Shigella dysenteriae – very severe
