Bacterial Disease - Clinical and Pathological Changes Flashcards
Commensal
- Stable polymicrobial communities present throughout life as part of ‘normal microflora’
- Found on skin and hollow organs whose surfaces are exposed to environment
- Acquired soon after birth
Pathogen
- Microorganism which causes disease
- Competes with normal microflora to gain foothold within niche
- Evades or overcomes host defences
- Expresses genes which encode factors which cause disease
Pathogenicity
Ability of a microbe to damage a host
Virulence
Relative capacity of pathogen to damage a host
Virulence factors
Bacterial traits that confer pathogenicity
* Adhesins
* Toxins
* Capsules
When do clinical consequences of infection occur?
When pathogenicity exceeds host defences
How do bacteria cause tissue damage?
Bacterial toxins
* Locally
* Systemically
Inflammatory reponse
Immune response
Outcomes of infection
- infection is eliminated and cleared
- Clinical disease occurs
* Acute
* Subacute
* Chronic - Subclinical infections
* carrier for disease
What determines shedding of agent?
Severity of disease
Type of pathogen
Tissues affected
Carrier state
Intermittent shedding of agent
Latent infection
Shedding of agent if disease is reactivated
Clinical changes in bacterial infections
Pathognomonic clinical presentation
Inflammatory response (non-specific to bacteria)
Cardiovascular consequences (in advanced stages)
Pathognomonic clinical presentation Example
Erysipelas in pigs
* Specific skin lesions
Inflammatory response
Non-specific to bacteria
○ Systemic
E.g. Pyrexia (^HR, ^RR)
○ Local
E.g. pain, heat, swelling, erythema
○ Pus – neutrophils – acute
○ Granulomas – macrophages – chronic
Cardiovascular consequences
Septicaemia
○ Congested mucous membranes
“Brick” or dark red
○ Toxic line
Purple line in gums near teeth – horses
