INFECTION

• A microorganism is an organism too small to be seen by the eye.
• Infection is the presence of microorganisms causing damage.

Relationship with humans:

• SYMBIOSIS- benefits human, no harm to microorganism
• MUTUALISM- benefits both hum & mircoorganism
• COMMENSALISM- benefits mircoorganism, no harm to human
• PATHOGENICITY- benefits mircoorganism, HARM to human
• OPPORTUNISM- a benigh (dormant) microorganism becoming pathogenic in response to a weakened human resistance-  opportunistic microorganisms wait to attack the host when defense systems are weakened-seizing their opportunity.

Process of Infection-4 stages of progression (microorganisms view):

• Colonisation - Infectious microorganisms exist in reservoirs transmitted through direct contact; indirectly by vectors; or direct exposure (faecal oral transmission).  The microorganism stabilizes adherence to the hosts tissue through specific receptors.
• Invasion - Infectious agents invade surrounding tissues/other sites, developing mechanisms to penetrate tissues and avoid the host's non specific (innate-inflammation) and specific (acquired-immunity) defences.
• Proliferation (Multiplication) - Host has a warm, nutrient filled environment for binary fission; rapid multiplication within infected cells (viral pathogens) and macrophages (bacterial pathogens).
• Transmission (Spread) - Localised infection if host immune system is intact; highly invasive microorganisms may enter other systems eg. lymphatic, blood (sepsis), organs if hosts immune or inflammatory system is compromised.  Successful spread relies on virulence factors.

Clincial Infection Process-4 stages (Infected host view):

·         Incubation Period- The interval between exposure to an infectious agent and the appearance of the first symptom - microorganism has already entered the host, colonised and begum multiplying.  Currently insufficient numbers to cause symptoms.

·         Prodromal Stage- The appearance of initial symptoms (mild, discomfort, tiredness) - Pathogens continue to multiply, general manifestations are now noticeable typically due to activation of the immune system eg. fever, pain, inflammation.

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