Introduction to Infection
Overview
Microbes are everywhere
There are many more microbes than hosts
The goal for both host and microbe is survival
Only a minority of times does microbe-host interaction cause problems (can even be symbiotic)
Microbes have been around much longer than us (3.5 billion years)
Types of Microbes
:
Bacteria, Fungi, Protozoa, Parasite, Viruses
Pathogen – cause of infection (non-pathogen does not)
Primary pathogen – causes a disease in any host
Opportunistic pathogen – only causes disease in immunocompromised hosts
The degree of pathogenicity is called virulence:
Multifactorial
Determinants are physiological for survival
Determinants that are important for infection.
Gram Negative Cell Wall:
Lipopolysaccharide – can accumulate and cause septic shock
The cell needs it to survive but is pathogenic to humans
Some microbes have genetic components specialized for pathogenicity
Host/Pathogen Interactions
Host Defences
Skin and mucosal secretions
Nonspecific intial local responses (pH, low iron)
Non-specific inflammatory responses (phagocytic cells)
Specific immune responses – (Lymphocytes)
against invasion: primary barriers
against evasion: local/tissue defenses
against multiplication: spread vs. localization damage
against toxins: specific immune response
Components of Host/Microbe Interaction
(1) Invasion of host through primary barriers
(2) Evasion of local and tissue host defenses by microbes
(3) Microbiological multiplication, with or without spread in the body
(4) Hosts immunologic ability to eliminate or control the microbe
most treatments have targeted the pathogen (antibiotics)
methods to enhance host response to the pathogen (immunotherapy) are now being developed
Immunology Against Bacteria
need a specific immune response
umulative effect of microbe and host reaction (septic shock)
Þ
damage = disease
Overt = clinical = not common
Covert = subclinical = common
All
microbes are killed by phagocytes
Extracellular pathogens
– multiply outside of host cells
Intracellular pathogens
– multiply inside host cells (viruses)
Lieshmania – Intracellular; very difficult to kill pathogen
Immunotherapy
- Ig’s Growth Factors for those who lack defenses
Vaccination
– our best bet against microbes; potential for eradication exists
Because of the way we live (world travel) earth is like a global community and disease can easily become pandemic.
Host defects –
asplenia
– no spleen or non-functioning (predisposed to encapsulated bacteria.
Toxic Shock syndome – was linked to a brand of tampon (P and G)
crisis in antibiotic resistance